SECTION 7

TRANSMISSION

CONTENTS OF THIS SECTION


Figure Index
Transmission-3-Speed
Troubles and Remedies
Specifications
Transmission-Overdrive
Troubles and Remedies
Special Tools


Powerglide Transmission
Specifications
Special Tools


Assembly Manual

Figure Index

A three-speed synchromesh transmission (fig. 1 and fig. 2) is used as standard equipment on all passenger cars. This transmission incorporates all helical gears which are machined from drop forged steel gear blanks, heat treated and shot peened for strength and long life. The shafts are machined from high grade steel, heat treated and ground to close limits.

The rear end of the clutch gear is supported by a heavy duty ball bearing at the front end of the transmission case and is piloted at its front end in an oil impregnated bushing mounted in the engine crankshaft. The front end of the mainshaft is piloted in a double row of roller bearings set into the hollow end of the clutch gear and the rear end is carried by a ball bearing.

The countergear is carried on roller bearings at both ends while thrust is taken on thrust washers located between ends of gear and front and rear of the case.

The reverse idler gear is carried on ball indented bronze bushings while thrust is taken on thrust washers located between ends of gear and front and rear of the case.

Gearshifting is manual through a concentric steering column gearshift mechanism (fig. 3) to the transmission cover located on the side of the transmission. Shifting is accomplished by two rotating cranks which directly engage the gears to be shifted, thus affording a highly efficient mechanical action. The shifter key for selection between first and reverse and second and high is contained in the lower end of the shifter tube and the two levers which it controls are carried on the shifter tube. Two shifter control rods connect the shifter levers on the transmission to the shifter tube levers.

Rotating motion created by moving the gearshift lever is transmitted to the levers on the shifter tube and thence to the shifter levers on the transmission cover, thus shifting into the selected gear.

Maintenance, Care and Adjustments

Gearshift Lever Adjustment

In cases where the gearshift linkage has been connected, it should be adjusted as follows:

1. Loosen swivel nuts, insert tool (fig. 1) in keyway in adjusting ring at bottom of mast jacket (fig. 2), through first and reverse shift lever and second and high lever.
2. Move both control rods until transmission is in neutral. Neutral detents must both be engaged to make this adjustment correctly. (To check, start engine with clutch disengaged, and release clutch slowly.)
3. Tighten swivel nuts and remove aligning tool.

NOTE: If most jacket lower dash clamp has been disturbed, at its mounting on dash, its eccentricity adjustment to the steering mainshaft should be followed as outlined in the procedure in Section 9 of this manual supplement.

Construction of Gearshift Control Lever

Alignment Gauge

In order to align lower control levers a tool made from an old hacksaw blade is suggested. The minimum length should be three inches. All details are shown in figure 1. This tool may be used in conjunction with tool number J-6041 from the 1955 Chevrolet special tools whenever mast jacket repair or alignment is necessary.

SPEEDOMETER DRIVEN GEAR

Disconnect speedometer cable, remove lock plate to housing bolt and lock washer and remove lock plate. Insert screwdriver in lock plate slot in fitting and pry fitting, gear and shaft from housing. Pry "O" ring from groove in fitting.

Install new "O" ring in groove in fitting and insert shaft.

Hold the assembly so slot in fitting is toward lock plate boss on housing and install in housing. Push fitting into housing until lock plate can be inserted in groove and attached to housing.

MAINSHAFT OIL SEAL

Removal

1. Remove nuts and U-bolts retaining rear universal joint trunnion bearings to the drive flange. Lower the rear of the propeller shaft and slide front flange off the mainshaft.
2. Insert oil seal remover tool J-5859 in oil seal and tap tool to seat it against step in housing. Tighten set screw to spread tool, then hammer seal from housing (fig. 5).

TRANSMISSION SIDE COVER ASSEMBLY

On any replacement of parts in the side cover assembly it is necessary to remove cover from transmission case.

1. Drain transmission and disconnect control rods from levers.
2. Remove cover assembly from transmission case.
3. Remove outer shifter lever clamp bolts and pull levers from shafts.
4. Remove nuts and locks and remove shifter interlock retainer. This will allow removal of shifter shaft and fork assembly, poppets and springs or interlock from cover.
5. Replace necessary parts and install shifter interlock retainer.
6. Install outer shifter levers on shafts and install clamp bolts.
7. With transmission gears in neutral and shifter forks in neutral, install cover to transmission using a new gasket. Tighten retaining cap screw securely. NOTE: Hump on first and reverse shifter fork (fig. 6) must be toward rear of transmission.
8. Attach control rods to shifter levers.
9. Fill transmission with 2 pints of SAE 90 transmission lubricant.

REMOVAL

1. Drain lubricant from transmission.
2. Disconnect the speedometer cable from speedometer driven gear fitting and disconnect shift control rods from the shifter levers at the transmission.
3. Remove nuts and U-bolts retaining rear universal joint trunnion bearings to the pinion drive flange. Lower the rear of the propeller shaft and slide to the rear to bring the front universal joint off the transmission output shaft.
4. Remove the 2 top transmission to clutch housing cap screws and insert 2 transmission guide pins, J-1126 in these holes.
5. Remove the 2 lower transmission to clutch housing cap screws.
6. Slide the transmission straight back on guide pins until the clutch gear is free of splines in the clutch disc. NOTE: The use of the 2 guide pins during this operation will support the transmission and prevent damage to the clutch disc through springing.
7. Remove transmission from under the body.

1. Remove the capscrews from the transmission side cover and remove the cover and gasket. NOTE: Under ordinary circumstances it is not necessary to disassemble the cover assembly. Servicing of cover is outlined under "Maintenance, Care and Adjustments."
2. Remove the four clutch gear bearing retainer screws and shakeproof washers and remove the retainer. Note the screw holes in the retainer are unevenly spaced so that the retainer may only be assembled to the case in one position, matching up the oil return slot with the hole in the case.
3. Install the special clutch gear and bearing puller J-937 by screwing the threaded sleeve (left-handed thread) onto the clutch gear shaft. Turning the puller handle will remove the gear and bearing without damage to mainshaft pilot bearings (fig. 7).
4. Remove 24 roller rear pilot bearings, 2 washers and 14 roller front bearings.
5. Remove extension to transmission case bolts and lock washers and pull extension and mainshaft out of transmission case, leaving second and third speed clutch assembly and first and reverse gear in case. Do not force mainshaft. Rotate mainshaft and second and third speed clutch gear to obtain alignment of clutching teeth and splines (fig. 8).
6. Remove the second and third speed clutch sleeve assembly and first and reverse gear through side opening in transmission case.
7. Remove the countershaft by driving it from the front to the rear of the case, using a soft steel drift. Remove the countergear rollers and the front and rear thrustwashers. NOTE: It is necessary to remove the countergear before removing the idler shaft, otherwise the idler shaft will strike the countergear.
8. Drive the idler shaft lock pin into the shaft. This pin is shorter than the diameter of the shaft so the shaft may be slipped out when the pin is driven in.
9. Using a drift pin, tap rear of shaft to drive out plug ahead of shaft. Do not turn the shaft while removing as the lock pin may drop down between the idler gear bushings.
10. Remove reverse idler gear and thrustwashers.
11. To remove mainshaft from extension, expand bearing snap ring and tap rear of shaft with a soft hammer to bring shaft, speedometer drive gear, second speed gear and bearing as an assembly forward out of extension (fig. 9).

Bearings

1. Wash the bearings thoroughly in a cleaning solvent.
2. Blow out the bearings with compressed air. CAUTION: Do not allow the bearings to spin but turn them slowly by hand. Spinning bearings will damage the race and balls.
3. After making sure the bearings are clean, lubricate them with light engine oil and check them for roughness. Roughness may be determined by slowly turning the outer race by hand.

Transmission Case

Wash the transmission case inside and outside with a cleaning solvent and inspect for cracks. Inspect the front face which fits against clutch housing for burrs and if any are present, dress them off with a fine cut mill file.

Gears

1. Inspect all gears and, if necessary, replace any that are worn or damaged.
2. Check the first and reverse sliding gear to make sure it slides freely on clutch sleeve.
3. Check the clutch sleeve to see that it slides freely on mainshaft.

Mainshaft, Rear Bearing, Second Speed Gear, and Speedometer Drive Gear (see fig. 9 and fig. 10 ).

Disassembly

1. Press speedometer drive gear off mainshaft, using suitable split plates in an arbor press.
2. Remove bearing to mainshaft snap ring and press bearing off shaft.
3. Remove second speed gear thrustwasher, pull drive pin out of shaft and remove second speed gear.

Assembly

1. Slide second speed gear on mainshaft, insert drive pin in shaft and Install thrustwasher against gear.
2. Install new bearing, groove in OD of bearing toward second speed gear.
3. Select one of four available snap rings so end play of bearing on shaft is a maximum of .004". This may be easily determined by installing successively larger rings. Use the thickest ring that will enter snap ring groove on shaft.
4. Start speedometer drive gear on shaft with chamfered I.D. of gear toward bearing. Press gear on shaft until forward face of gear is 7/8" from rear face of bearing.

Clutch Gear Bearing

Removal

1. Place the clutch gear in a vise with soft jaws, and remove the bearing retainer nut and oil slinger, using the special wrench J-933 (fig. 11). The retaining nut and oil slinger is a one piece steel casting machined with a left handed thread and is locked in place on the clutch gearshaft by being staked into a hole provided for that purpose.
2. To remove the clutch gear bearing place the special press plate J-936 over the gear and against the bearing. Using an arbor press, press the shaft out of the bearing (fig. 12).CAUTION: Do not attempt to drive the shaft out of the bearing or the bearing will be seriously damaged.

Installation

1. Using an arbor press, press the clutch gear bearing on to the clutch gear with the locating ring toward the front of the gearshaft so that the bearing will enter the case to the maximum possible depth.
2. Install the combination clutch bearing retaining nut and oil slinger on the clutch gearshaft and draw it up tight, using special wrench J-933.
3. Lock the retaining nut oil slinger in place by staking it into the hole with a center punch. Care must be used not to damage the threads on the shaft. CAUTION: The bearing must turn as freely after it is installed to the shaft as it turned before being placed on the shaft.

Disassembly

1. Remove the first and reverse sliding gear.
2. Turn the synchronizer ring in the clutch sleeve until the ends of the synchronizer ring retainer can be seen through the slot in the clutch sleeve.
3. Using special pliers J-932 fig. 13 expand the retainer into the counterbore in clutch sleeve. This raises the retainer from the groove in the ring so ring may be easily slipped out
4. Check the synchronizing cones for wear or for being loose in the clutch sleeve. If cones are damaged in any way, it will be necessary to replace the clutch sleeve assembly and both synchronizer rings.
5. Inspect the synchronizer rings for smoothness.
6. Place the synchronizer rings in the synchronizing cones and check with thumbs to see that rings do not rock. Excessive rocking indicates a poor fit between the rings and cone, which will not permit proper synchronizing of gears during shifting.

Assembly

1. Install the synchronizer ring retainers in the counterbores in the ends of the clutch sleeve.
2. Using special pliers J-932 in slot in clutch sleeve, expand each retainer in the counterbore, lubricate each synchronizer ring with light oil, and install clutch sleeve. NOTE: Make sure retainers seat in groove all the way around the rings so rings will turn freely.
3. Install the first and reverse sliding gear on the clutch sleeve.

Synchronizer Energizing Spring

1. It will be noticed upon examining these springs that one of the ends is slightly offset. Each spring must be assembled in its groove in the clutch gear and the second speed gear with the offset or locking end between the third and fourth teeth of either of the two banks of teeth on these gears, thus keeping the spring from turning in its groove (fig. 14).
2. Under normal operation it should never be necessary to replace the energizing springs; however, should an energizing spring be removed for any reason, a new spring should be installed. The spring may be removed by slipping a thin blade under the spring and raising it sufficiently to slide it off over the clutch gear teeth.CAUTION: In replacing either energizing spring, be very careful not to distort the spring when expanding it over the clutch teeth.

1. The bushings used in the idler gear are pressed into the gear then peened into holes in the bores to lock them into place, and are accurately bored with special diamond boring tools. This insures the positive alignment of the bushings and their shafts, as well as proper meshing of the gears. Because of the high degree of accuracy to which these parts are machined, the bushings are not serviced separately.
2. Check bushings for excessive wear by using a narrow feeler gauge between the shaft and the bushing. The proper clearance is from .002" to .004".

Countergear Needle Bearings

All countergear needle bearings should be inspected closely and if excessive wear shows they should all be replaced as well as the shaft.

Assembly

Reverse Idler Gear

1. Lubricate the reverse idler thrustwashers and install the gear and thrustwashers in the transmission case with the gear having the chamfered teeth to the rear of the case.
2. Install the idler shaft, making sure that the lock pin hole in the shaft lines up with the hole in the case at the same angle (fig. 15).
3. Use a new idler shaft lock pin, coat the pin with Permatex and drive it in approximately 1/16" beyond flush with case; peen the hole slightly. This lock pin must be a tight fit in the case to prevent oil leaks.
4. Install the idler shaft expansion plug in the case. A new plug should be used whenever possible.

Countergear

1. Place some cup grease in the roller bearing area of each end of the countergear and install the 25 rollers in each end. The grease will hold the rollers in place while installing (fig. 16).
2. Insert countergear assembly tool J-5777 (fig. 17) in countergear.
3. Apply grease to thrustwashers and place one at each end of countergear.
4. Insert the countergear (with tool J-5777) in transmission case and align tool with countershaft holes in the case.
5. Lubricate and insert countershaft in rear of case, pushing assembly tool out front of case (fig. 18).
6. Turn countershaft so flat on end of shaft is horizontal and at the bottom of shaft. Make sure front end of shaft is in line with hole in front of case, and drive shaft into case until flat on shaft is flush with rear of case.NOTE: The flat on shaft must be horizontal and at the BOTTOM or the transmission case extension cannot be assembled to transmission case. On overdrive equipped transmission, flat must be horizontal and at TOP of shaft to engage the overdrive adapter.

Install the synchronizing clutch sleeve assembly, with first and reverse sliding gear, in transmission case.

Mainshaft

1. Install the mainshaft assembly in the transmission case extension, or in the overdrive adapter.
2. Install gasket on transmission case.
3. Align lugs on synchronizer rings with slots in mainshaft helical spline, and turn second speed gear on mainshaft so lugs on the synchronizer rings slide in slots on gear. Push the shaft into the clutch sleeve until transmission case extension (or the overdrive adapter) is tight against case. Install bolts and lockwashers.

Clutch Gear and Bearing

1. Place some cup grease in the mainshaft pilot hole in the clutch gear and install the two groups of roller bearings, the 14 group and small I.D. spacer, then the large I.D. spacer and the 24 group (fig. 19). After being assembled in the pilot hole, these bearings will lock themselves in place and cannot fall out. Install the clutch gear in the transmission case.
2. Using a brass drift, tap the outer race of the clutch gear bearing until the bearing locating ring seats against the case, being careful to drive the assembly straight to prevent damage to the mainshaft pilot and pilot bearing. CAUTION: During this operation make sure that the synchronizer ring lugs line up with the slots between the clutch teeth on the clutch gear.
3. Install the clutch gear bearing retainer and gasket, making sure that the oil slot in the retainer lines up with the oil slot in the front face of the transmission case. Do not allow the gasket to protrude beyond the edge of the retainer.
4. Install the retainer screws, using the special shakeproof washers. Tighten the retaining cap screws to 10-12 ft. lbs. torque.

1. Install guide pin in upper right transmission to clutch housing bolt hole for alignment and place transmission on guide pin. Rotate transmission as necessary, start clutch gear shaft into clutch disc and slide transmission forward.
2. Install the two lower transmission mounting bolts and lockwashers and tighten securely. Remove guide pin and install upper mounting bolts and lockwashers and tighten securely.
3. Install propeller shaft. Align yokes and install U-bolts and nuts which retain rear trunnion bearings to pinion flange and tighten securely.
4. Connect first and reverse and second and third control rods to shifter levers at side cover.
5. Check and adjust linkage as necessary as outlined under "Maintenance Care and Adjustments."
6. Remove speedometer driven gear and add 1/2 pint transmission lubricant to housing. Reinstall speedometer driven gear.
7. Connect speedometer cable to driven gear and tighten securely.
8. Fill transmission with lubricant.

SYNCHRO-MESH TRANSMISSION

Symptom and Probable Cause
Probable Remedy

Slips Out of High Gear

a. Transmission loose on clutch housing.
a. Tighten mounting bolts

b. Dirt between transmission case and clutch housing.
b. Clean mating surfaces.

c. Misalignment of transmission.
c. Shim between transmission case and clutch housing.

d. Clutch gear bearing retainer broken or loose
d. Tighten or replace clutch gear bearing retainer.

e. Damaged mainshaft pilot bearing.
e. Replace pilot bearing

f. Shifter lock spring weak.
f. Replace spring.

g. Clutch gear or second and third speed clutch improperly mated.
g. Replace clutch gear and second and third speed clutch.


Slips Out of Low and/or Reverse

a. Worn first and reverse sliding gear.
a. Replace worn gear.

b. Worn countergear bearings.
b. Replace countergear bearings and shaft.

c. Worn reverse idler gear.
c.Replace idler gear.

d. Shifter lock spring weak or broken.
d. Replace spring.

e. Improperly adjusted linkage.
e. Adjust linkage.


Noisy in All Gears

a. Insufficient lubricant.
a. Fill to correct level.

b. Worn countergear bearings.
b. Replace countergear bearings and shaft.

c. Worn or damaged clutch gear and countershaft drive gear.
c. Replace worn or damaged gears
.
d. Damaged clutch gear or mainshaft ball bearings.
d. Replace damaged bearings
.
e. Damaged speedometer gears.
e. Replace damaged gears.


Noisy in High Gear

a. Damaged clutch gear bearing.
a. Replace damaged bearing.

b. Damaged mainshaft bearing.
b. Replace damaged bearing.

c. Damaged speedometer gears.
c. Replace speedometer gears.


Noisy in Neutral with Engine Running

a. Damaged clutch gear bearing.
a. Replace damaged bearing.

b. Damaged mainshaft bearing.
b. Replace damaged bearing.


Noisy in All Reduction Gears

a. Insufficient lubricant.
a. Fill to correct level.

b. Worn or damaged clutch gear or counter drive gear.
b. Replace faulty or damaged gears.


Noisy in Second Only

a. Damaged or worn second speed constant mesh gears.
a. Replace damaged gears.

b. Worn or damaged countergear rear bearings.
b. Replace counter gear bearings and shaft.


Noisy in Low and Reverse Only

a. Worn or damaged first and reverse sliding gear.
a. Replace worn gear.

b. Damaged or worn low and reverse countergear.
b. Replace countergear assembly.


Noisy in Reverse Only

a. Worn or damaged reverse idler.
a. Replace reverse idler.

b. Worn reverse idler bushings.
b. Replace reverse idler.

c. Damaged or worn reverse countergear.
c. Replace countergear assembly.


Excessive Backlash in Second Only

a. Second speed gear thrustwasher worn.
a. Replace thrustwasher.

b. Mainshaft rear bearing not properly installed in case.
b. Replace bearing, lock or case as necessary.

c. Universal joint retaining bolt loose.
c. Tighten bolt.

d. Worn countergear rear bearing.
d. Replace countergear bearings and shaft.


Excessive Backlash in All Reduction Gears

a. Worn countergear bushings.
a. Replace countergear.

b. Excessive end play in countergear.
b. Replace countergear thrustwashers.


Leaks Lubricant

a. Excessive amount of lubricant in transmission.
a. Drain to correct level.

b. Loose or broken clutch gear bearing retainer.
b. Tighten or replace retainer.

c. Clutch gear bearing retainer gasket damaged.
c. Replace gasket.

d. Cover loose or gasket damaged.
d. Tighten cover or replace gasket.

e. Operating shaft seal leaks.
e. Replace operating shaft seal.

f. Idler shaft expansion plugs loose.
f. Replace expansion plugs.

g. Countershaft loose in case
g. Replace case.

Transmission Specifications

Type Mainshaft

Type
   Selective Synchromesh
Speeds
   Three forward - one reverse.
Location
   In unit with engine
Gears - Type
   All helical
Bearings
   Clutch Gear...........................Ball Bearing
   Countershaft...........50 Rollers-1/8" Dia. x 3/4"
   Mainshaft
      Front Pilot......14 Rollers-3/16" dia. x 33/64"
      Rear Pilot..........24 Rollers-1/8" dia. x 1/2"
      Mainshaft Rear.....................Ball Bearing
   Reverse Idler Bushing (front and rear)......Bronze
Gear Ratio
   First....................................2.94 to 1
   Second...................................1.68 to 1
   Third....................................1.00 to 1
   Reverse..................................2.94 to 1
Service Data
   Mainshaft Rear Bearing End Play..........003" max.
   Reverse Idler Gear Bushing Clearance.. .002"-.004"
   Second Speed Gear Endplay...Approx.......... .010"

TORQUE SPECIFICATIONS

Clutch Gear Bearing Retainer Cap 
   Screws..........................10-15 ft. lbs.

Side Cover Retaining Cap Screws....15-18 ft. lbs.

The overdrive unit (fig. 20 and fig. 21) is essentially a two-speed planetary transmission attached to the rear of a conventional three-speed transmission. In overdrive, engine speed is approximately 30 percent slower at a given road speed since the drive train includes planetary gears which provide a lower overall gear ratio than that obtained in high gear with the conventional transmission.

The electrical equipment which controls the automatic action of the mechanical portion of the overdrive unit consists of a solenoid, a speed sensitive governor switch, a relay and a kickdown switch. The circuit including this equipment makes it possible to operate in overdrive above a pre-set cut-in speed, or in conventional drive at any speed.

OPERATION

Highway Driving

When the car is operated below a predetermined "cut-in" speed, varying from 26 to 30 mph, the direct drive is used, making available the acceleration so desirable at lower speeds. As the car speed increases above the cut-in point the overdrive unit will shift into the overdrive ratio, but only when the driver desires no further acceleration; when consciously, or unconsciously, he lifts his foot from the accelerator, whereupon the shift is completed. Thereafter, the overdrive remains in effect until the car speed falls below the "cut-out" point, when the overdrive is released.

However, at high speeds, the driver while operating in overdrive may require additional acceleration, beyond that available by opening the throttle wide. His natural impulse is to press the accelerator further, and this act releases the overdrive, making available the full acceleration of direct drive. The direct drive is retained so long as the full acceleration is required; when the driver no longer requires it he unconsciously lifts his foot from the accelerator, whereupon the overdrive is resumed. If the driver so desires, he may retain the direct drive indefinitely by maintaining a small amount of throttle opening.

City Traffic Driving

Much city driving is under conditions which permit speeds up to 35 mph, with frequent stops. Many drivers are accustomed to start in second gear under such conditions. With overdrive equipped cars, the driver may start in second gear, accelerate up to the cut-in speed, and, by merely lifting the foot from the accelerator pedal, engage the overdrive-second gear combination. At the first traffic stop, it is merely necessary to release the clutch; the gearshift lever is not touched. Furthermore, If a special burst of acceleration is needed in a tight traffic spot, the full power of second gear may be had by pressing the accelerator to the floor, resuming the overdrive-second by the usual method of closing the throttle.

Use of Clutch Pedal

At speeds below the overdrive cut-in point, the free-wheeling action of the overdrive unit makes it possible to do all gearshifting without releasing the main clutch. Above cut-in speed, it is necessary to release the clutch for shifting gears, and likewise, the clutch must be released when the car is being started from standstill, and whenever it is being brought to a stop.

Mechanical

Free-Wheeling Direct Drive

The transmission mainshaft (fig. 22) extends thru the sun gear and is splined into the pinion cage and roller clutch cam. The latter has 12 cam surfaces, and 12 clutch rollers located against these surfaces by means of the roller retainer and the roller retainer spring. When a driving torque is applied against the cam, the rollers are forced outward into wedging contact with the outer race (fig. 23), thus driving the car. Under such driving conditions, all the overdrive gears and their directly-associated control parts revolve together as a unit.

When the driving torque is removed from the cam, the rollers release their wedging contact (fig. 23), permitting the roller clutch to overrun, with the mainshaft, pinion cage, and engine turning at a slower speed than the ring gear, output shaft, and propeller shaft. Under such conditions, the ring gear will turn faster than the pinion cage, and the sun gear will turn slower. In fact, the sun gear may turn forward, stand still, or turn backward, depending solely upon the relative speeds of the transmission mainshaft, and the output shaft. If the mainshaft is turning at exactly 70% of the speed of the output shaft, the sun gear will stand still; if it turns faster than this, relatively, the sun gear will turn forward; and if it turns-slower, the sun gear will turn backward. If the engine is idling with the car moving forward, this reverse rotation may be quite fast.

Overdrive

At car speeds below 26 to 30 mph (the "cut-in" speed), the electrical control system is completely inactive. Assuming that the car is being accelerated below the 26 to 30 mph cut-in speed with the dash control pushed in (fig. 22), the sun gear control plate revolves along with the sun gear at the speed of the transmission mainshaft. Under such circumstances, the blocker ring, by its frictional drag upon the hub of the control plate, is rotated into such a position as to latch the control pawl against inward movement (fig. 24).

When the car reaches the cut-in speed, the governor contacts close, acting through the overdrive electrical circuits to energize the solenoid. The latter sets up a spring pressure against the pawl, tending to push it into engagement. This movement is prevented by the blocker. However, the driver, either unconsciously, or consciously, and according to his own choice, may momentarily close the throttle, whereupon the roller clutch releases, and the engine slows down. At the same time, the sun gear slows down, more rapidly, so that the sun gear passes through the standstill condition when the engine speed has fallen 30%, and then reverses its motion. Upon the instant of reversal, the blocker ring, moved by its frictional drive from the control plate hub, also rotates slightly in this direction and releases the pawl which snaps into the first notch of the backwardly-rotating control plate (fig. 24). With the sun gear thus held against rotation, (fig. 25), the pinion cage, and hence, the engine, will revolve through only 0.7 turn for each turn of the propeller shaft (fig. 26).

The extreme rapidity of the pawl engagement insures that the control plate cannot rotate backward more than 3/8 turn at the most; usually, it will be less. This engagement, at nearly perfect synchronism, accounts for the smooth action of this control. Once engaged, under the conditions of normal driving, the overdrive is in action until the car speed falls to a value 4 or 5 mph lower than the cut-in speed, when the governor contacts open, releasing the solenoid, which withdraws the pawl (if throttle is closed), whereupon the condition of free-wheeling direct drive is resumed.

Driver Controlled Downshift (Kickdown)

It has been noted, above, that when the overdrive is engaged, the engine turns only 0.7 as fast as when in direct drive. This reduces the power available (excepting at high car speeds) and although this reduced power is usually sufficient for all purposes, there are times when it is desirable to return to direct drive, for more power, without reducing the car speed to the point where the overdrive would normally release.

Under such circumstances, the driver merely presses the accelerator pedal to the wide-open position. Through suitable electrical Controls, this releases the solenoid, urging the pawl toward release from the control plate. However, due to the driving torque reaction, the pawl is held, and cannot move to release until the torque is momentarily relieved. This is accomplished by interrupting the ignition, whereupon the pawl snaps to release, which immediately restores the ignition. When the overdrive has been thus disengaged the roller clutch carries the direct drive, and the driver may hold it in this condition at his pleasure, until he chooses to re-engage overdrive by merely lifting his foot from the accelerator, momentarily. Thereupon the overdrive is resumed, unless the car speed has in the meantime fallen below the overdrive release point.

Conventional Drive

Although the normal procedure is to operate the unit as above, taking advantage of the freewheeling and the overdrive, there are times, as when descending long, steep grades, where it may be desirable to use the frictional drag of the engine as a brake. Under such circumstances, the overdrive dash control may be pulled out, swinging the control lever (fig. 27) forward, thus moving the shift rail and shift fork backwards, shifting the sun gear so that the lockup teeth will engage the corresponding teeth of the pinion cage. This causes the entire group of working parts to revolve as a unit, duplicating in all respects the action of the conventional transmission: In order to thus lock up the unit, if the car is in motion, it is necessary to open the throttle, to assure that all parts revolve together, or to release the overdrive, if engaged, by pressing the accelerator pedal to the floor pulling out the overdrive dash control at the same time. Thereafter, the car will have the usual conventional drive until the driver chooses to push the overdrive dash control in, which may be easily done at any time.

Since the roller clutch will not transmit a reverse drive, it is necessary for the lock up mechanism to be used whenever reverse drive is desired. This is done, automatically, by the transmission reverse shift mechanism, which pushes the shift rail to the rear, independently of the overdrive control lever, whenever the transmission is shifted into reverse.

Electrical

Solenoid

The overdrive solenoid is mounted on the left side of the overdrive adapter. The solenoid contains two windings, a hold-in and pull-winding. The hold-in winding (dashed line, figure 28) consists of many turns of fine wire and remains energized as long as the overdrive is in operation. The pull-in winding (solid line) contains fewer turns of heavier wire and is necessary to create a magnetic field strong enough to start and complete the solenoid plunger movement. Once this movement is completed the hold-in winding alone is sufficiently strong to maintain the plunger in. the "bottomed" position. Therefore, as the plunger moves into the "bottomed" position, the pull-in circuit is broken by a built-in stop which opens a pair of spring-loaded contact points which are normally closed. Another pair of contact points within the solenoid, also spring-loaded but normally open, are permitted to close by movement of the "pawl rod" when the overdrive becomes engaged. The pawl rod is a part of the solenoid plunger assembly which extends outside the solenoid case.

The end of this rod is shaped to interlock with a movable pawl (fig. 24) in the overdrive unit. Solenoid operation causes the pawl alternately to engage or disengage with a control plate which is a part of the overdrive unit. The control plate, when engaged by the pawl holds the sun gear of the overdrive unit against rotation to permit overdrive operations. The control plate, when not engaged by the pawl, rotates freely with the sun gear and conventional operation of the transmission is obtained.

Governor

The governor switch mounted on the right side of the overdrive housing, is operated by centrifugal force. It prohibits overdrive operation until the car has reached a predetermined cut-in speed at which time the electrical contacts close.

Relay

The solenoid relay mounted on the left front of the dash panel is essentially a switch which is operated electromagnetically. When current flows through a winding in the relay, contacts in the relay are closed by the magnetic pull created by the winding.

Kickdown Switch

The kickdown switch is mounted on a bracket secured to a carburetor mounting stud. It is a mechanical switch containing two sets of electrical contacts. One set of contacts is normally open and the other normally closed. When this switch is actuated by the driver pushing the accelerator down to the wide open position, the normally closed contacts are opened and the normally open contacts are closed.

Wiring

There are three separate circuits within the overdrive circuit (fig. 28); (1) control circuit, (2) solenoid circuit, and (3) ground-out circuit.

Control Circuit

The control circuit includes the relay winding and the electrical contacts located in the kickdown, and governor switches. Both sets of contacts must be closed to permit solenoid operation. When this circuit is completed, the relay becomes energized and the relay contacts close. As long as both sets of contacts remain closed, the relay contacts remain closed.

Solenoid Circuit

The solenoid circuit includes the relay contacts and the solenoid windings. With the closing of the relay contacts, the solenoid becomes energized and moves the pawl toward the slot in the control plate until blocked from further movement by the blocker ring within the overdrive gear case (fig. 24). The pawl becomes spring-loaded by the final movement of the solenoid plunger which compresses the pawl rod spring. Under these conditions, the blocker ring will slide from under the pawl whenever the driver momentarily lifts his foot off the accelerator. This brief reduction in engine torque allows the pawl to engage the control plate (fig. 24) and the overdrive becomes operative.

As the solenoid plunger completes its movement, it opens a set of contacts in series with the pull-in winding as already described. Since the hold-in winding alone is sufficiently strong to maintain the plunger in the "bottomed" position, the amount of current drawn by the solenoid thus is reduced during overdrive operation. As the pawl moves into engagement with the control plate, completion of the pawl rod travel permits closing of the spring-loaded solenoid contacts in series with the ground-out circuit. The overdrive system will remain in operation as long as the solenoid remains energized. The relay opens and the solenoid is de-energized when the control circuit is broken at the kickdown, or governor switch.

Ground-Out Circuit

The ground-out circuit (dashed line, figure 28) is connected in parallel electrically with the distributor contact points and includes the normally open contacts within the kickdown switch, as well as the normally-open solenoid contacts (connected to the No. 6 terminal of the solenoid) which close as the overdrive becomes operative. When the kickdown switch is actuated during overdrive operation, the ignition coil primary winding is grounded through these two sets of contacts, and the control circuit is opened at the same time. The momentary grounding of the ignition circuit causes the engine to miss and, since the overdrive control circuit is open, allows disengagement of the overdrive. As the overdrive disengages and the pawl rod retracts, the ground-out circuit is opened within the solenoid and conventional car operation is resumed.

Maintenance, Care and Adjustments

Servicing of the overdrive governor switch and pinion, the sun gear solenoid, oil seal and cable bracket, the output shaft rear oil seal, the control shaft lever, and the speedometer driven gear (fig. 20) may be accomplished without removing the overdrive from the vehicle, as discussed in the following paragraphs:

GOVERNOR SWITCH AND PINION

To remove governor switch, disconnect wires at governor switch and screw governor out of housing, using tool J-4653 on the flat hexagonal surface of governor case. The pinion may be separated from the governor by removing the snap ring on the shaft.

SUN GEAR SOLENOID, OIL SEAL AND CONTROL CABLE BRACKET

Remove the solenoid by taking out the two mounting bolts and lock washers, removing the cable bracket with the lower bolt. Turn the solenoid 1/4 turn and pull solenoid plunger out of adapter. The oil seal may be pried out of the adapter.

OUTPUT SHAFT OIL SEAL

Removal

1. Remove nuts and U-bolts retaining rear universal joint trunnion bearings to the drive flange. Lower the rear of the propeller shaft and slide to the rear to bring The universal joint front flange off the output shaft.
2. Insert oil seal remover, tool J-5859 in oil seal and tap tool to seat it against shoulder in housing. Tighten set screw to spread tool, then hammer seal from housing.

Installation

1. Coat outside of new oil seal with a suitable sealant and start seal into bore in overdrive housing.
2. Using oil seal driver J-5154A, drive oil seal into bore.
3. Install propeller shaft by sliding universal joint front flange on output shaft and installing rear universal joint trunnion bearing nuts and U-bolts.

CONTROL SHAFT LEVER AND OIL SEAL

To remove the control shaft oil seal, disconnect the control cable, remove tapered pin and pull lever out. Then pry out oil seal with a sharp punch.

Coat outside of new oil seal with suitable sealant and start seal straight into counterbore in housing. Using a suitable driver having an outside diameter of 15/16", drive seal into place. Insert shaft through seal and install tapered pin. Connect control cable to lever.

SPEEDOMETER DRIVEN GEAR

Disconnect speedometer cable, remove lock plate to housing bolt and lock washer and remove lock plate. Insert screw driver in lock plate slot in fitting and pry fitting, gear and shaft from housing. Pry "O" ring from groove in guide.

Install new "O" ring in groove in fitting and insert shaft.

Hold the assembly so slot in fitting is toward lock plate boss on housing and install in housing. Push fitting into housing until lock plate can be inserted in groove and attached to housing.

Major Service Operations

With the overdrive assembly removed from the transmission, service operations on the transmission proper are the same as for the standard three-speed transmission.

Repairs to the overdrive housing, output shaft, ring gear assembly, clutch cam, roller retainer, pinion cage, sun gear, shift rail, sun gear control plate, output shaft bearing, oil seal, speedometer drive gear, solenoid pawl and interlock plunger may be performed underneath the car by removing the overdrive housing without disturbing the transmission.

If the transmission mainshaft, overdrive adapter or transmission rear bearing which is retained in adapter require replacement, the entire transmission and overdrive assembly should be removed and overhauled on the bench.

NOTE: Due to X-member interference on convertible models, the transmission and overdrive assembly must be removed.

Overdrive Housing

Removal

1. Place car on stand jacks.
2. Remove drain plugs and drain transmission and overdrive.
3. Disconnect wires from solenoid and from governor switch.
4. Disconnect speedometer cable from driven gear fitting.
5. Remove nuts and U-bolts retaining rear universal joint trunnion bearings to the drive flange. Lower the rear of the propeller shaft and slide shaft to rear to bring the universal joint front flange off the output shaft.
6. Remove speedometer driven gear fitting, gear and shaft.
7. Disconnect control cable from control lever.
8. Drive out the control shaft tapered pin (fig. 29) and pull control shaft out.
9. Remove seven bolts and lock washers attaching the overdrive housing to the transmission case and adapter.
10. Pull overdrive housing including overdrive output shaft and ring gear assembly to rear, being careful to keep adapter from pulling away from transmission case (fig. 30) (catch the clutch rollers as they drop out of the retainer). CAUTION: If adapter moves away from transmission case the transmission mainshaft pilot needle bearings will drop out of clutch gear and necessitate disassembly of transmission.
11. Remove gasket from adapter and install one bolt removed from housing to hold the adapter to the transmission case.

Disassembly

Fig. 40

1. Remove governor and pinion if not previously removed.
2. Pierce plug in rear bearing snap ring access hole in top of housing and pry plug out of housing.
3. Spread rear bearing snap ring with snap ring pliers and lightly tap end of shaft with a soft hammer to free bearing from snap ring (fig. 31), then pull shaft, including ring gear, speedometer drive gear and rear bearing, from housing.
4. Remove shift rail retractor spring from housing.
5. Remove output shaft rear bearing snap ring from housing.
6. Press bushing from rear of housing, using tool J-5778.
7. Remove ring gear snap ring (large) and slide ring gear off shaft (fig. 32). The oil collector ring is spun securely to the shaft to form an oil tight seal.
8. Remove speedometer drive gear (small) snap ring from output shaft.
9. Support front face of bearing and tap end of shaft to start speedometer drive gear off shaft. If necessary to use arbor press to start gear (fig. 33) do not press shaft more than 3/8" through bearing or woodruff key in shaft may gouge bearing. Pull gear off shaft.
10. Remove woodruff key and slide bearing off shaft.

Cleaning and Inspection

As each part is removed from the housing assembly, wash in clearing solvent, dry, and protect from subsequent dirt accumulation.

Inspect housing, shift rail retractor spring, snap rings, gears and bearings for cracks, defects or damage and substitute new parts where necessary.

If clutch rollers show surface markings of any kind they should be replaced.

A general inspection of the overdrive parts remaining on the transmission mainshaft, particularly the clutch cam and roller retainer assembly and the shift rail and fork assembly, should be made at this time.

Assembly

1. Slide rear bearing straight on shaft with snap ring slot in bearing closer to ring gear end of shaft.
2. Install woodruff key in shaft, start speedometer drive gear onto shaft and align keyway in gear with key in shaft. Tap gear tight against bearing and install small snap ring.
3. Engage ring gear on teeth of overdrive shaft and install large snap ring in ring gear.
4. Using tool J-5778, press bushing into housing flush with bore for seal.
5. Install output shaft rear bearing snap ring in slot in housing.
6. Install shift rail retractor spring inside housing and insert long 3/8" drift pin through spring to align spring with holes in housing.
7. Slide output shaft assembly into housing until rear bearing contacts snap ring. Spread snap ring and push shaft in until snap ring engages bearing.
8. Install new plug in snap ring access hole in top of housing.

Removal

1. Remove overdrive housing, output shaft and ring gear assemblies as outlined in preceding pages.
2. Pull "U" clips at each end of clutch cam (fig. 34) and slide the cam and roller retainer from pinion cage hub and transmission mainshaft. If roller retainer or cam is to be replaced separate these pieces by pulling retainer out until the hooked ends of spring can be pulled out of holes in cam.
3. Slide pinion cage assembly off sun gear and mainshaft.
4. Remove sun gear and shift rail assemblies from shaft (fig. 35). Shift rail collar may be separated from sun gear by removing snap rings at either end of collar. Shift rail, fork, and spring may be separated by removing snap ring between cupped washer and shift fork.
5. Remove sun gear solenoid, oil seal and cable bracket (fig. 36).
6. Remove large snap ring from adapter (fig. 37) and remove sun gear control plate retainer. Then slide control plate and blocker ring out of adapter (fig. 38). If control plate or blocker ring is to be replaced they may be separated by pulling blocker ring off plate.
7. Lift sun gear pawl out of adapter.

Cleaning and Inspection

As each part is removed from the rear of the transmission, wash in cleaning solvent, dry, and protect from subsequent dirt accumulation.

1. Inspect "U" clips, control plate retainer, control plate, blocker ring and pawl for defects or damage and substitute new parts where necessary.
2. Inspect the fit and tension of the blocker ring on hub as follows:
   • Push one end of ring toward the other. The ring should grip and hold to the hub. If the ring does not hold when correctly installed (flat surface of ring facing out), it should be replaced.
   • Push one end of ring away from opposite end and check the frictional drag required to slide the ring around the hub as follows: (1) Hold one lug of control plate in a soft jawed vise and hook a spring balance into the notch of the nearest blocker ring lug (fig. 41). (2) Measure the pull required to rotate the ring after it has started moving. The pull should be 4-6 pounds on new parts, which will fall to 1-1 1/2 pounds when thoroughly broken in. While low friction may be corrected by squeezing the ring together for a tighter fit, installation of new parts is recommended.
3. Inspect the clutch cam and if the 12 flat surfaces show slight lengthwise indentations, replace the cam. If rollers show markings of any kind, they should all be replaced.
4. Test the tension of the cam retaining springs after the assembly has been thoroughly washed. (The springs are designed to twist the cam to return the rollers to the high side of the cam). Hold hub of cam and turn roller retainer counterclockwise, then release retainer. The retainer should snap back quickly. If the action is slow or retarded, replace the springs or the complete assembly. NOTE: If the spring tension is weak or retarded, the unit will free-wheel at all times.
5. When installing springs be sure both springs are coiled in the same direction (clockwise when looking toward flanged end of retainer), with "S" end of springs hooked into holes in retainer (fig. 42) and opposite ends hooked into holes in cam.
6. Inspect the shift rail, fork, and spring for cracks, burrs or damage and replace defective parts.
7. When shift rail, fork and spring are assembled, make sure the parts bear the correct relationship as shown in fig. 43, with snap ring inside cupped washer.

Installation

1. Insert sun gear pawl in adapter with notched side up.
2. If blocker ring was removed from control plate, position ring on plate with flat surface of ring facing out, then start the assembly over transmission mainshaft with ring toward rear. Slide the assembly into position with slot in ring toward sun gear pawl (fig. 38).
3. Slide control plate retainer over mainshaft, against control plate and install snap ring in adapter.
4. Install solenoid oil seal, solenoid, and cable bracket.
5. Start the sun gear onto the mainshaft. Hold shift rail so arm of fork fits in collar on sun gear and forward end of shift rail enters opening in adapter and transmission case (fig. 35). Slide both assemblies forward so pin in adapter locates the fork, and sun gear engages control plate.
6. Install pinion cage assembly over mainshaft and sun gear, turning cage assembly clockwise to engage sun gear.
7. If free wheeling cam and roller retainer were separated, assemble these parts by positioning springs so both are coiled clockwise when looking at flanged end of retainer (fig. 42), then place retainer over slotted end of cam, hook free ends of springs in holes in cam, turn retainer clockwise and push springs into place around cam.
8. Slide cam and roller retainer assembly over mainshaft and pinion cage hub. Install "U" clips at each end of free wheeling cam.

OVERDRIVE HOUSING

Installation

1. Snap a tight fitting rubber band around clutch cam roller retainer, insert rollers under rubber band in retainer and, with low gear of transmission engaged, turn retainer and rollers counterclockwise until rollers are in their low position.
2. Remove the one bolt holding adapter to transmission case and install gasket on case.
3. Position shift rail so flat for control shaft faces outward, then start housing, output shaft and ring gear assembly into place with shift rail entering spring in housing (fig. 44). Slide housing against adapter. Install seven bolts and lockwashers to adapter and case.
4. Install control shaft lever oil seal, shaft and lever and connect control cable to lever.
5. Install governor assembly and speedometer driven gear, shaft and fitting.
6. Install propeller shaft.

Lubrication

The transmission and overdrive unit are connected with oil passages so the same oil is used for both. However, the following precautions must be used in the filling, in order that the proper amount of oil may be carried.

1. In making the initial filling, first fill the overdrive unit with the proper oil, until oil runs out the filling hole, then replace plug. Fill the transmission with the same type of oil, until oil runs out the filling hole, then replace plug.
2. In subsequent filling (at each chassis lubrication), inspect the transmission only, for oil level, and fill as necessary.

OVERDRIVE RELAY

The operation and purpose of this relay is discussed within the write-up on the Overdrive Circuit and its operation. Specifications and checking procedures for this relay are as follows:

Specifications*
Air Gap ........................011 inch minimum
Point Opening ..................025 inch
Closing Voltage ................8.3-10.7 volts
Armature Sealing
Voltage........................ 11.2 volts maximum
*Preliminary figures subject to revision.

Three checks and adjustments are required on the overdrive relay: air gap, point opening and closing voltage. The air gap and contact point opening checks and adjustments should be made with the battery disconnected.

Air Gap

The air gap should not normally require adjustment unless the relay has been misadjusted. Check the air gap with the points barely touching and adjust if necessary by bending the lower point support (fig. 45).

Point Opening

Check the contact point opening and adjust by bending the upper armature stop (fig. 46).

Closing Voltage

To check the relay closing voltage, connect a potentiometer or variable resistance of sufficient value (not less than 50 ohms) in series with the "KD" terminal, connect a voltmeter to the "IGN" and "Y-D" terminals. With the ignition switch on, slowly decrease the amount of resistance in order to check the relay closing voltage (the overdrive solenoid and relay should click when the relay closes). Adjust the closing voltage by bending the armature spring post (fig. 47). Bend down to increase the closing voltage and bend up to decrease the closing voltage.

To check the sealing voltage, increase the voltage after the relay closes until the armature seals against the core. Decrease the sealing voltage by reducing the relay air gap.

Solenoid

Closing Coil

Remove solenoid from transmission, connect a jumper wire between positive terminal of battery and mounting flange of solenoid. Connect a second jumper wire between the battery negative terminal and solenoid terminal No. 4; this should cause the solenoid pawl to move out. If solenoid chatters, Hold-In Coil is defective.

Engaging Spring

With jumper wire connected as in paragraph above, (solenoid energized, plunger extended) place ball end of solenoid against bench. Push down on solenoid. The pawl rod should move in 3/8" under a load of not less than 8 lbs. nor more than 12. Pawl should move out to extended position when load is removed.

Ignition Grounding Contact

Place a test lamp between negative battery terminal and solenoid terminal No. 6. Lamp should light when this connection is made. Remove jumper from between negative battery terminal and solenoid terminal No. 4. Pawl rod should snap "in" and test lamp should go out.

GOVERNOR SWITCH

Remove overdrive wire at governor and connect test lamp between governor overdrive terminal and negative terminal of battery. Drive car on road or raise on jacks. The lamp should light at a car speed of between 26 to 30 mph. Upon decreasing speed, the lamp should go out at between 28 and 23.5 mph. The car speed differential between light "on" and light "off" should be 2 or 3 mph.

KICKDOWN SWITCH

Disconnect wires at kickdown switch and install test harness to kickdown switch but do not connect test harness to overdrive harness.

1. Connect test lamp between "SW" terminal and negative terminal of battery; with switch in normal position, lamp should light when "REL" terminal is grounded but should not light when "IGN" or "SOL" terminals or switch case is grounded.
2. Connect test lamp between "IGN" terminal and negative terminal of battery; with switch stem pushed in, lamp should light when "SOL" terminal is grounded, but should not light when "SW" or "REL" terminals or switch case is grounded.

Troubles and Remedies

Mechanical

Any one of the following general complaints may be due to non-standard mechanical conditions in the overdrive unit:

1. Does not drive unless locked up manually.
2. Does not engage, or lock-up does not release.
3. Engages with a severe jolt, or noise.
4. Free-wheels at speeds over 30 mph.

These troubles may be diagnosed and remedied as described in the following paragraphs.

1. Does not drive unless locked up manually.
   • Occasionally, the unit may not drive the car forward in direct drive, unless locked up by pulling the dash control. This may be caused by one or more broken rollers in the roller clutch, the remedy for which is the replacement of the entire set of rollers.
   • This may also be caused by sticking of the roller retainer upon the cam. This retainer must move freely to push the rollers into engaging position, under the pressure of the two actuating springs.
   • Sometimes this is due to slight indentations, worn in the cam faces by the rollers spinning, remedied by replacement of the cam.
2. Does not engage, or lock-up does not release.
   • Dash control improperly connected-Unless the overdrive dash control wire is connected to the lockup lever on the left side of the overdrive housing in such a manner as to move the lever all the way back when the dash control knob is pushed in, it may hold the shift rail in such a position as to interlock the pawl against full engagement resulting in a buzzing noise when overdrive engagement is attempted. To correctly make this connection, loosen binding post at lever, pull dash control knob out 1/4 in., move lever all the way to the rear, and tighten binding post.
   • Transmission and overdrive improperly aligned-The same symptoms as above may also result from misalignment, at assembly, of the overdrive housing to the transmission case, resulting in binding of the overdrive shift rail, so that the retractor spring cannot move the rail fully forward, when the dash control knob is pushed in, and the transmission is not in reverse. Under such conditions, the unit may remain fully locked up. To test for this, be sure that the transmission is not in reverse; disconnect the dash control wire from the lockup lever, and feel the lever for free forward movement. If the lever can be moved forward more than 1/4 in., it indicates that misalignment probably exists. To correct this, loosen the capscrews between the overdrive housing and transmission case, and tap the adapter plate and overdrive housing until a position is found where the rail shifts freely; tighten capscrews.
   • Kickdown switch improperly adjusted the position of the kickdown switch should be adjusted, by means of the two large nuts which clamp the switch shank, so the switch plunger travels 3/16 in. before the throttle lever touches its stop. Occasionally the large nuts which clamp the switch through the switch bracket are tightened sufficiently to bend the switch shank, thus preventing free motion of the switch stem. This may usually be remedied by loosening the upper of the two nuts.
   • Improper installation of solenoid-If car cannot be rolled backward under any circumstances and there is no relay click when the ignition is turned on, it probably indicates that the solenoid has been installed directly, without twisting into the bayonet lock between solenoid stem and pawl, thus jamming the pawl permanently into overdrive engagement. If the car will occasionally roll backwards, but not always, (and there is no relay click when the ignition switch is turned on) it may indicate that, upon installation, the bayonet lock was caught, and the solenoid forcibly twisted into alignment with the attaching flange, thus shearing off the internal keying of the solenoid. Under these circumstances, the end of the solenoid stem may not catch in the pawl, and upon release of the solenoid, the pawl will not be withdrawn promptly from engagement, but may simply drift out. If the solenoid stem end has its two flats exactly facing the two solenoid flange holes, it will not withdraw the pawl properly. If the stem can be rotated when grasped by a pair of pliers, it indicates that the internal keying has been sheared.
   • Improper positioning of blocker ring occasionally, either in assembly at the factory, or in service operations in the field, the internal parts of the overdrive unit may have been rotated with the solenoid pawl removed, causing the blocker ring to rotate, so that its two lugs are not located with respect to the pawl as shown in fig. 24 and fig. 38. In other words, the solid portion of the blocker ring may be in alignment with the pawl, which will prevent full engagement of the pawl with the sun gear control plate. To test for this condition, remove solenoid cover, pull dash control knob out, roll car 2 ft. forward. Push dash control in, turn ignition switch on. Then ground the "KD" terminal of relay, and watch movement of center stem of solenoid. It should not move more than 3/8 in. when the solenoid clicks. Then, with the relay terminal still grounded, shift into low gear, and roll car forward by hand. Solenoid stem should then move an additional 3/8 in., as the pawl engages fully. These two tests indicate proper blocker action. Unless both tests are met, the blocker ring is probably not in the correct position.
3. Engages with a severe jolt or noise. Insufficient blocker ring friction may cause the ring to lose its grip on the hub of the sun gear control plate. Check the fit and tension of the ring as described under "Cleaning and Inspection."
4. Free-wheels at speeds over 30 mph. If cam roller retainer spring tension is weak the unit will free-wheel at all times. Check spring action as described under "Cleaning and Inspection."

Any one of the following general complaints may be due to electrical trouble. n the overdrive circuit.

1. Does not engage.
2. Does not release.
3. Does not kickdown from overdrive.

These troubles may be traced and remedied as described in the following paragraphs.

1. Does not engage.
   • With the ignition switch on, ground the "KD" terminal of the solenoid relay with a jumper lead. If the solenoid clicks, the relay and solenoid circuits are in operating condition. If no click is heard in the relay, check the fuse and replace if defective.
   • If the fuse is good, use a second jumper lead to connect the "SOL" and "BAT" terminals of the relay. If a click is now heard in the solenoid, the relay is probably at fault and should be repaired or replaced.
   • If the solenoid does not click in Step b, check the wiring to the No. 4 terminal of the solenoid and replace if necessary. If the wiring is not defective, the trouble is probably in the solenoid. Remove the solenoid cover, examine the solenoid contacts in series with the pull-in winding and clean if necessary. Test again for clicks, as in Step b, after replacing solenoid cover and lead wires. Replace the solenoid if trouble has not been corrected.
   • If the relay and solenoid circuits are in good condition as determined in Step a, leave the ignition switch on and make sure the manual control knob is in the overdrive position. Ground one and then the other of the two terminals next to the stem of the kickdown switch (identified as "SW" and "REL"). If the solenoid clicks when one terminal is grounded but not the other, replace the switch. If the solenoid does not click when either of the terminals is grounded, check the wiring between the relay and the kickdown switch and replace if defective.
   • If the solenoid clicks as each terminal is grounded in Step d, ground the governor switch terminal. If the solenoid clicks, the governor switch may be defective. If the solenoid does not click, check the wiring between the kickdown and governor switches and replace if necessary.
2. Does not release
   • Remove the connection to the "KD" terminal of the relay. If this releases overdrive, look for a grounded control circuit between the relay and governor switch.
   • If the overdrive is not released in Step a, disconnect the lead to the "SOL" terminal of relay. If this releases the overdrive, replace the relay.
3. Does not kickdown from overdrive
   • With the engine running, connect a jumper lead between the No. 6 terminal of the solenoid and ground. Operate the kickdown switch by hand. This should stop the engine. If it does, the solenoid is probably defective and it should be checked for dirty ground-out contacts or other defects within the ground-out circuit of the solenoid (fig. 28). Clean the contacts or replace the contact plate as required.
   • If the engine does not stop in Step a, ground one and then the other of the two terminals (Identified as "IGN" and "SOL") farthest from the stem of the kickdown switch. The engine should stop when one of the two terminals (IGN) is grounded. If the engine does not stop when either of the terminals is grounded, the wiring or connections to the switch between the switch and coil are defective. When the other terminal (SOL) is grounded, the engine should stop when the kickdown switch is operated. If the engine does not stop when the kickdown switch is operated with the second terminal grounded, the kickdown switch is defective. If the trouble is in the kickdown switch, adjust the linkage to give more travel of the switch rod. If this does not correct the trouble, replace the kickdown switch.
   • If the kickdown switch operates as it should, check for an open circuit in the wiring between the kickdown switch and the No. 6 terminal of the solenoid.
   • If the trouble is not located by the above checks, the upper contacts of the kickdown switch may not be opening. To check for this condition, ground the overdrive control circuit at the governor switch. This should cause the solenoid to click. Operate the kickdown switch by hand. This should cause a second click as the solenoid releases. If there is no second click, adjust the linkage to give more travel of the switch rod. If this does not correct the trouble, replace the kickdown switch.

Control of the Powerglide transmission is obtained by positioning a shift control lever mounted at the top of the steering column.

The control lever can be positioned in the following five positions:.

Parking

Neutral

Drive

Low

Reverse

To make it easy for the driver to find the location of the range desired, the shift control quadrant is marked with the letters, "P," "N," "D," "L," and "R." To shift into parking, or reverse range, it is necessary to raise the shift control lever against a light spring pressure.

PARKING

When placed in the parking position, the shift control lever engages a parking lever pawl which locks the transmission planet carrier to the transmission case. This parking lock must never be applied when the car is in motion.

NEUTRAL

The neutral position is to be used when the car is standing still with the engine running, or when towing the car. It permits accelerating the engine with no car movement.

DRIVE

In drive position the vehicle is in automatic range. It starts in low range and upshifts automatically, depending on the extent to which the accelerator is depressed.

LOW

Low range is used only when the "going," is particularly tough, such as in sand or on long steep grades. On long steep grades, low range prevents premature upshifting and a resultant loss of acceleration which would occur if in "D" range. Low range can also be used to obtain additional engine braking when descending steep hills but not above 45 mph.

The shift from "low" to "drive" range or vice versa may be made while the car is in forward motion, but not in excess of 45 mph.

REVERSE

The reverse range is used to move the car in a reverse direction.

CAUTION: It is advisable not to drive at high speeds for any distance when in this range for damage to the clutch plates may result.

Starting the Engine

The starter on cars equipped with -the Powerglide transmission is so wired that the engine will not start unless the shift control lever is in either "park" or "neutral" position.

PUSHING TO START ENGINE

If it ever becomes necessary to push a car equipped with a Powerglide transmission, the control lever should be left in the "N" position until the car has reached a speed of approximately 25 to 30 mph. At this speed the turbine is spinning fast enough to turn the converter pump and the rear oil pump has developed sufficient pressure to engage the low band. Then place the control lever in the "L" range.

CAUTION: It is recommended that the car be pushed rather than to be towed, because when the engine starts, it is apt to accelerate into the rear end of the towing vehicle.

TOWING A DISABLED CAR

A car equipped with Powerglide transmission must not be towed on its rear wheels except in Neutral (N) and should not be towed in excess of 30 mph. If it is towed with the transmission in any of the driving ranges unnecessary damage to the transmission may result because the rear pump would be in operation.

If the car has been damaged in a collision to the extent that the control lever on the steering column cannot be positioned in Neutral (N), it will be necessary to disconnect the long control rod at the idler lever and place the transmission in Neutral (N) as follows:

1. Remove the cotter pin from the long control rod and disconnect it from the idler lever on the left side of transmission case.
2. Push the idler lever toward the rear of the car as far as it will go; this places -the transmission in Reverse position. Then move the idler lever toward the front from this position to the third detent which is Neutral (N) position.

If for any reason the transmission is locked up the car must not be towed on its rear wheels or serious damage to the transmission will result.

Maintenance

OIL REQUIREMENTS

The Powerglide transmission requires an oil known as Automatic Transmission Fluid, "Type A" bearing a "AQ-ATF" number. This oil is available through Chevrolet dealers and oil company filling stations in sealed containers.

OIL LEVEL

The transmission oil level should be checked every 1000 miles. Oil should be added only when the level is below the "FULL" mark on the dip stick with oil hot or at operating temperature. The oil level dip stick is located in the engine compartment on the right side just opposite the starter (fig. 1). In order to check oil lever accurately, the engine should be idled with the transmission oil hot and the control lever in neutral (N) position.

It is important that the oil level be maintained no higher than the "FULL" mark on the transmission oil level gauge. DO NOT OVERFILL, for when the oil level is at the full mark on the dip stick, it is just slightly below the planetary gear unit. If additional oil is added, bringing the oil level above the full mark, the planetary unit will run in the oil, foaming and aerating the oil. This aerated oil carried through the various oil pressure passages (low servo, reverse servo, clutch apply, converter, etc.) may cause malfunction of the transmission assembly, resulting in cavitation noise in the converter and improper application of bands or clutches.

If the transmission is found consistently low on oil, a thorough inspection should be made to find and correct all external oil leaks. The mating surfaces of servo cover, governor cover, converter housing, transmission case, low and drive valve body cover, side cover and transmission case extension should be carefully examined for signs of leakage. The transmission case extension rear oil seal should also be checked. All test plugs should be checked to make sure that they are tight and that there is no sign of leakage at these points. The plug in the bottom of the converter housing should also be removed. Any appreciable quantity of oil draining from this opening would indicate leakage at the converter cover "O" ring seal, front pump "O" ring seal, front pump seal or blocked passage in front pump.

DRAINING AND REFILLING

Every 25,000 miles the transmission should be drained and refilled. The transmission should be warmed up before draining. Draining is accomplished as follows:

1. Remove transmission case drain plug. This drains oil from transmission case. CAUTION: Do not start engine while draining assembly.
2. After transmission is completely drained, install transmission case plug.
3. Remove dip stick, start engine and with selector lever in neutral "N" position, refill transmission with 41/2 quarts of Automatic Transmission Fluid, "Type A" using oil filler tube and funnel J-4264 (fig. 2).NOTE: This oil filler tube and funnel is vented. The transmission is not vented and if not properly vented when filling will cause blow back and oil spillage.
4. Allow engine to idle a few minutes until oil is hot or at operating temperature and with the selector lever in neutral (N) position, check oil level to see that the oil level is up to the full mark on the dip stick. Add oil as required but DO NOT OVERFILL. CAUTION: Oil must be hot when making this oil level check.

The Powerglide transmission requires three service adjustments; a simple positive linkage adjustment, neutral safety switch adjustment, and a throttle valve linkage adjustment.

Positive Linkage Adjustment

1. Loosen the shifter tube lever clamp nut sufficiently to allow the upper control rod to move freely in the swivel.
2. Push the control rod bellcrank, on the left side of the transmission case, toward the front of the car as far as it will go. This places the transmission in Park (P) position.
3. Place the shift control lever, which is mounted at the top of the steering column, in Park (P) position.
4. Then, with both the control rod bellcrank and the shift control lever held in the Park (P) position tighten the shifter tube lever clamp nut securely. This completes the adjustment.

Neutral Safety Switch

All cars equipped with Powerglide Transmission are provided with a neutral safety switch which prevents operation of the starting motor except when the transmission is in Neutral (N) or Park (P) positions. This switch is a safety feature installed for the purpose of preventing car motion when starting the engine. It is mounted on the steering gear mast jacket between the dash and instrument panel. It is important, therefore, that this switch be maintained in proper adjustment.

Adjustment

1. Loosen one of the switch assembly mounting screws and remove the other.
2. Place the selector lever in the neutral "N" position.
3. Center visible elongated slot in mounting switch with tapped hole in mast jacket. Tighten securely the screw that was loosened. Then install remaining screw and tighten securely.

If, after the switch is so positioned, the engine will not turn over, loosen the screws and rotate the switch in the direction necessary until it does. Be sure the selector lever is in the neutral position when performing this operation.

Throttle Valve Linkage Adjustment

A throttle valve linkage adjustment is required to maintain correct relationship between the accelerator pedal, carburetor and throttle valve in the low drive valve body. The transmission throttle valve is connected through linkage to the carburetor and the accelerator pedal. Throttle valve pressure is, therefore, variable and dependent on carburetor throttle opening. Adjustment of throttle linkage is important to maintain correct pressure relationship in the transmission which controls the transmission shift range. Adjustment of the throttle valve linkage should be accomplished as follows:

(a) On six cylinder models:

1. With the selector lever in "D" range and hand brake set, adjust engine idle to 425 rpm with engine at normal operating temperature and transmission warm. After idle is set "shut off" engine. NOTE: Automatic Choke must be entirely off and throttle stop screw against low step on fast idle cam.
2. Disconnect rod "C" (fig. 3) from throttle lever "E."
3. Remove the extreme lower rear low and drive body cover bolt and lockwasher.
4. Rotate the throttle valve control outer lever assembly counterclockwise to the open throttle position (to a definite stop). Hold in this position and with throttle valve outer lever positioning gauge, J-5906 set at 6 3/8", measure the distance between the hole in the side cover and hole in throttle lever (fig. 4). If the pins of the gauge will enter holes, adjustment of lever "E" is correct. If adjustment is not correct, loosen lever to clamp attaching bolt and holding clamp as recommended adjust outer lever as necessary.
5. Connect rod "C" to lever "E."
6. Disconnect rod "B" from carburetor throttle valve lever and rod "D" from accelerator and throttle valve lever on cylinder block.
7. With idle set as outlined in step 1 and rod "C" forced forward against stop in transmission (open throttle), adjust rod "B" for free entry of swivel pin in carburetor throttle valve lever, with the carburetor throttle valve in the (wide open position).
8. Then, with carburetor throttle valve held in the (wide open position) and accelerator pedal rod to the floor (fully depressed) adjust rod "D" for length required for free entry of swivel pin in bellcrank.

(b) On eight cylinder models:

1. With the selector lever in "D" range and hand brake set, adjust engine idle to 425 rpm with engine at normal operating temperature and transmission warm. After idle is set "shutoff" engine. NOTE: Automatic choke must be entirely off and throttle stop screw against low step on fast idle cam.
2. Disconnect rod "F" (fig. 5) from throttle lever "E."
3. Remove the extreme lower rear low and drive body cover bolt and lockwasher.
4. Rotate the throttle valve control outer lever assembly counterclockwise to the open throttle position (to a definite stop). Hold in this position and with throttle valve outer lever positioning gauge, J-5906 set at 2 7/8", measure the distance between the hole in the side cover and hole in the throttle lever (fig. 4). If the pins of the gauge will enter the holes, adjustment of lever "E" is correct. If adjustment is not correct, loosen lever to clamp attaching screw and holding the clamp as recommended adjust outer lever as necessary.
5. Connect rod "F" to lever "E".
6. Disconnect rods "B" and "G" from carburetor throttle valve lever.
7. With idle set as outlined in step 1 and rod "F" forced forward against stop in transmission (open throttle) adjust rod "G" for free entry of swivel pin in carburetor throttle valve lever, with the carburetor throttle valve in the (wide open position).
8. Then, with the carburetor throttle valve held in the (wide open position) and the accelerator pedal t6 the floor (fully depressed), adjust rod "B" for free entry of swivel pin in carburetor throttle valve lever.

The ideal transmission is one which will automatically provide the suitable speed or power ratio between the engine and the driving members to meet all driving conditions with minimum effort on the part of the operator.

Chevrolet's Powerglide transmission (fig. 6) meets these ideal qualifications because it offers a combination of torque converter drive and automatic shifting, that enables the vehicle to cope with variable road and traffic conditions.

The design and operation of the transmission will be described under the following headings:

1. Torque Converter
2. Planetary Unit and Clutch
3. Hydraulic System
4. Hydraulic Operation

TORQUE CONVERTER

One of the features of the Powerglide transmission is its ability to provide a smooth application of power from the engine to the rear wheels. The engine's power is its ability to provide sufficient torque (twisting power) to the rear wheels to maintain car speeds. The torque from the engine is sufficient, without transmission multiplication, to keep the car in motion (fig. 7) except in starting, accelerating or when hill climbing.

This increase and multiplication of engine torque may be accomplished by a gear transmission or through the use of a hydraulic unit which provides hydraulic torque conversion or a combination of both.

Hydraulic torque conversion means multiplying engine torque by changing fluid velocity into power. Torque conversion, therefore, provides an infinite number of gear ratios up to 2.1 to 1 (fig. 8).

Chevrolet's torque converter is a fluid unit (fig. 9) having three elements:

1. A pump mounted in a housing driven by its rim which is bolted to the flywheel.
2. A turbine, which is fluid driven by the pump and attached through a hub to the transmission input shaft.
3. A stator mounted on an overrunning clutch on a stator support (fig. 9).

The torque converter is supplied with oil under pressure to prevent cavitation and provide for cooling.

The pump, or driving member is designed with 31 curved blades placed radially on the inside of a housing which is driven by the engine. An inner ring reinforces the blades and forms the desired path for the oil. As the pump rotates, fluid is thrown through the curved fluid passages in the turbine.

The turbine is the driven or output member of the converter and is spline mounted through its hub to the transmission input shaft. Its design is similar to that of the pump except that it has 33 blades curved opposite to the pump blades. Fluid thrown from the pump blades hits the turbine blades and causes the turbine to rotate which in turn rotates the transmission input shaft.

The stator is mounted through a free wheeling clutch to a stator hub which is splined to the stator support held solidly in the transmission case. The stator is a reactionary member which receives oil from the turbine and changes its flow to the direction of pump rotation, thereby assisting the pump.

Operation

In the torque converter the vanes are curved so as to get the desired amount of power from the pump and turbine. The pump blades are curved in a backward direction from the direction of rotation which gives added acceleration to the oil as it leaves the pump rim. The vanes in the turbine are also curved to absorb the required amount of energy from the oil as it passes through the turbine. To be able to do this the vanes are curved in a manner that causes the oil to be discharged from the center of the turbine in a direction opposite to rotation of the turbine. As the oil leaves the turbine blades at the center it still has a lot of kinetic energy left and due to the curvature of the turbine blades, It would exert- this energy against the blades of the pump and hinder its operation unless some means were provided for turning the flow to assist the pump.

We have means of giving directional control to the oil as it leaves the turbine and enters the pump. This is accomplished by interposing a stator between the pump and turbine with vanes so curved that they will change the direction of the oil discharged from the turbine and cause it to flow in the same direction as the rotation of the pump (fig. 10). Now, instead of oil bucking the pump and interfering with it, the unexpended energy in the oil is actually helping the pump do its job. The stator thus becomes a reactionary member assisting the function of the pump giving torque conversion. Through this assistance, it takes less engine power to drive the pump, the engine is able to deliver more power to the turbine and torque multiplication of 2.1 to 1 can be obtained as power to drive the rear wheels.

As the rotational speed of the turbine increases, the direction of the oil flow from the turbine exit changes, so that it exerts a force on the back of the stator vanes. This condition would cause turbulence resulting in increased friction and power loss. Therefore, the stator is mounted on a free wheeling clutch which locks in a direction opposite to that of the pump and turbine rotation. As the turbine speed approaches pump speed the stator free wheels and is carried along with the rotating oil mass.

Planetary Unit and Clutch

The planetary unit and clutch of the Chevrolet Powerglide Transmission (fig. 11) is a complete unit within itself containing a hydraulic clutch assembly and a planetary gear set to furnish drive, reverse, an emergency low and neutral. The hydraulic clutch assembly is built up into a clutch drum, which includes a clutch piston, clutch spring and piston seals; nine clutch plates, five of these plates are steel externally splined to the clutch flange while four plates are steel, faced on both sides with a combination facing of paper and cork.

These four plates are internally splined to the clutch hub which in turn is splined to the input shaft. These parts are retained inside the drum by a clutch flange, flange retainer and retainer ring. The clutch flange is splined to a low sun gear.

When oil pressure is applied to the clutch piston, the clutch plates are pressed together, which connects the clutch drum to the clutch hub and the input shaft. This engagement of the clutch causes the low sun gear to rotate with the input shaft.

When oil pressure to the clutch is released, the clutch spring returns the piston to free the clutch plates. This disengages the clutch.

The outer diameter of the clutch drum is used for low range band application. Application of the low band bolds the low sun gear stationary.

The planetary unit consists of the rev se sun gear, low sun gear, short and long pinions, a reverse ring gear and drum and a planet carrier.

In the planet carrier assembly, there are two sun gears, the reverse sun gear and the low sun gear. The reverse sun gear is splined to, and always turns with the input shaft. The low sun gear may revolve freely until the low band or the clutch is applied.

The reverse sun gear is in mesh with three long pinions and the long pinions are in mesh with three short pinions. The short pinions are in mesh with the low sun gear and reverse ring gear.

Both the long pinions and the short pinions are mounted on- and revolve about planet pinions pins which are solidly fastened to the planet carrier which is part of the output shaft.

The reverse sun gear and short pinions always rotate in the same direction. Band or clutch application, however, determines whether the output shaft rotates in a forward or reverse direction.

Operation

Automatic Drive

When the selector lever is placed in the automatic drive "D" range which is the normal driving range and the accelerator is depressed, the car starts forward and the transmission is in the low range (fig. 12). The clutch is released and the brake band applied to the outside diameter of the clutch drum. With the brake band applied, the clutch drum is held stationary which in turn holds the clutch flange stationary. The clutch flange which is splined to the low sun gear holds the sun gear stationary. Drive then is through the input shaft, to the reverse sun gear to the long pinions to the short pinions which are in mesh with the low sun gear. Since the low sun gear is held stationary with the brake band applied, the short pinions will walk around the low sun gear and as they walk around the sun gear they carry the output shaft, to which they are attached, with them at a reduction of 1.82 to 1.

The transmission will automatically shift to the high range at approximately 12 to 50 mph depending to what extent the accelerator pedal is depressed. When this shift occurs, the brake band is released and the clutch is applied which locks the planetary system causing it to rotate as a unit. With the clutch applied, the clutch hub which is splined to the input shaft is tied to the clutch flange through the medium of the clutch plates. The clutch flange is splined to the low sun gear. The low sun gear is meshed to the short pinions, the short pinions are meshed with the long pinions and the long pinions are meshed with the reverse sun gear which is splined to the input shaft. Drive then is through the input shaft to the reverse sun gear to the long pinions to the short pinions to the low speed sun gear. Since the low speed sun gear is locked to the input shaft through the clutch flange, clutch plates and clutch hub, the entire unit will revolve at turbine speed (fig. 13). This is known as high range.

Emergency Low Range

In emergency low, as in starting forward in Automatic Drive, the clutch is released and the brake band is applied to the outside diameter of the clutch drum. Therefore, the same mechanical action takes place as when starting in Automatic Drive. However, hydraulic action differs in that the manual valve in the main valve body is so positioned that it blocks off the passages to the low and drive valve body eliminating the possibility of an automatic shift into high range.

Reverse

In reverse it is necessary to turn planet carrier which is part of output shaft in a direction opposite to that of input shaft (fig. 14).

With the selector lever in the reverse position, the clutch and low band are released and the reverse band is applied to the reverse drum. With the band applied to the drum the reverse internal gear which is part of the drum is held stationary. Drive then is through the input shaft, to the reverse sun gear to the long pinions to the short pinions. Since the short pinions are meshed with the reverse internal gear which is held stationary when the band is applied, the short pinions will walk around inside the internal gear in a reverse direction carrying the output shaft to which they are attached with them at a reduction of 1.82 to 1.

Neutral

In neutral the output shaft remains stationary.

With the selector lever in the neutral position, the clutch and low and reverse bands are released, consequently there is no reaction member to provide positive drive. All gears are free to spin around their own axis and no motion is imparted to the planet carrier in any direction.

The Hydraulic System

Oil Supply

Eleven quarts of Automatic Transmission Fluid "Type A" are carried in the oil sump and converter to operate the transmission and its hydraulic controls.

Oil Pumps

Two oil circulating pumps of the internal external gear type are incorporated in the transmission design. The transmission front pump has the greater capacity and is driven by the engine. The transmission rear pump has less capacity and is driven by the output shaft.

The requirements of the front pump are greater because when starting the car and when operating at low road speed or in reverse, the pump must be of adequate size to immediately furnish all the oil needed at required pressures.

The rear, pump can be smaller because its output is not fully used until the car has reached a speed of approximately 35 mph. The capacity of the smaller pump is sufficient at this time, due to its rpm, to furnish all the oil needed at required pressures. The use of the smaller rear pump at higher speeds conserves horsepower.

The rear pump is required to operate the low range band when pushing the car to start the engine.

A pressure regulator valve limits the pressure output of the pumps. At times either one or both pumps are used to supply the requirements of the transmission.

Controls

Range selection within the transmission is accomplished by means of a control lever under the steering wheel connected to a manual valve inside the main valve body in the transmission.

Manual Valve

The manual valve is used to direct oil to low drive valve body, reverse and low pistons and to lubrication in neutral or park. Figure 15 identifies oil passages of the valve body.

Pressure Regulator Valve

The pressure regulator valve is operated by oil pressure acting against calibrated spring pressure and has the following functions:

1. It regulates pressure of front and rear pumps.
2. It keeps a constant supply of oil to the converter when the engine is running and partially prevents oil draining out of the converter when the engine is not running.

The pressure regulator valve functions in the following manner:

When the engine is not running the position of the pressure regulator valve is as shown in (fig. 16). When the engine is started, the front pump supplies oil to the manual control valve and pressure regulator valve. The oil, under pressure enters the pressure regulator in the area between the second and third land. From this area it continues through the check valve and then back to the pressure regulator valve in the area between the first and second land.

The valve body gasket has a small opening, equivalent to a .062" diameter orifice, through which oil flows into a dash pot beneath the first land of the valve. As pressure begins to build up behind the land, the valve starts moving against the spring as shown (fig. 17) and opens the converter feed line. This occurs at approximately 50 psi.

When the oil pressure behind the first land reaches approximately 87 psi, the pressure regulator valve has moved far enough against its spring to contact the pressure regulator reverse booster valve moving it against its spring. As this takes place a channel is opened permitting excess oil to return to the pump suction line. The pressure regulator valve and booster valve move back and forth to control the pressure of the oil for whatever the load requirements.

Action of Check Valve

The check valve in starting or at low speeds is closed to the rear pump pressure line as the rear pump has not attained sufficient volume and pressure to be effective. The higher pressure from the front pump holds the valve closed. This prevents the oil from the front pump bleeding off through the rear pump. In Figure 15, when the car is being driven above approximately 35 mph, road load, the rear pump is being rotated fast enough to create sufficient pressure to operate the transmission. At this time the rear pump overcomes the front pump pressure, opens the check valve to rear pump pressure and closes the valve to the front pump pressure line.

Pressure Regulator Reverse Booster Valve Assembly

The pressure regulator reverse booster valve assembly (fig. 17) is located in the servo cover. It consists of a booster valve, booster valve spring, booster valve spring seat, guide and valve guide spring and the valve operates on both spring pressure and hydraulic pressure. This valve has two functions. Spring pressure applied to the outer end of the valve assists in regulating pressures in Automatic Drive, Emergency Low, Neutral and Park. Hydraulic pressure applied to the outer end of the valve in reverse only in addition to spring pressure brings about the increased operating pressure necessary.

In reverse, higher oil pressure is required to hold the band applied. To obtain the necessary pressure for holding the band oil is channeled from the reverse servo apply line, through the reverse servo cover, to the reverse booster valve. This pressure opposes the pump pressure being exerted on the pressure regulator valve, causing the system pressure to increase.

Converter Pressure Regulator Valve (fig. 15)

When the engine is started oil is directed to the converter through an orifice uncovered by the pressure regulator valve. Oil circulates through the converter and is returned to lubrication through an orifice restricted by the converter pressure regulator valve. This valve seals oil in the converter up to a pressure of approximately 10 psi and assists the pressure regulator valve in preventing drain down of the converter. This prevents cavitation when starting the engine.

Closed Throttle Downshift Cushion Valve and Forced Downshift Cushion Valve

A closed throttle downshift cushion valve and a forced downshift cushion valve are incorporated in the main valve body. Their purpose is to provide for correct application of the low band under various driving conditions. The closed throttle downshift cushion valve is sensitive to main line pressure and, therefore, is affected by engine speed conditions. The forced downshift cushion valve is sensitive to governor pressure and, therefore, is affected by vehicle speeds. These valves function as follows:

(a) Neutral to Drive or Neutral to Low (Engine at Idle).

When the selector lever is placed in either "D" or "L" range, the closed throttle downshift cushion valve is held closed by its spring (fig. 18), because with the engine idling main line pressure is less than 65 psi which is insufficient to overcome the spring. The forced downshift cushion valve is open, however, for it is sensitive to governor pressure and since governor pressure is not available on a shift of from either Neutral to Drive or from Neutral to Low there is no force available to overcome its spring. Main line pressure is, therefore, directed to the apply side of the low servo piston through the .107" drilled orifice in the valve body, which provides for slow, smooth band application.

(b) Neutral to Drive or Neutral to Low (Engine at Fast Idle).

When the selector lever is placed in either "D" or "L" range main line pressure is great enough to overcome the closed throttle downshift cushion valve spring and opens the valve (fig. 19). The forced downshift cushion valve is open, however, for as explained, it is sensitive to governor pressure and none is available under these conditions. Main line pressure, therefore, by-passes the .107" drilled orifice and applies. pressure to the apply side of the low servo piston through the large passage.

(c) Throttle Downshift - Drive to Low below 25 mph.

On a throttle downshift below road speeds of 25 m h the forced downshift cushion valve is held open by its spring (fig. 19) because at road speeds below 25 mph governor pressure is not great enough to overcome it. The closed throttle downshift cushion valve is also open for at road speeds above 12 mph main line pressure is great enough to overcome its spring. This allows main line pressure to by-pass the .107" drilled orifice and apply pressure to the apply side of the low servo piston through the large passage. This provides for rapid band application to accommodate engine torque, thus preventing engine runaway.

(d) Throttle Downshift - Drive to Low above 25 mph.

On a throttle downshift above road speeds 25 mph the forced downshift cushion valve is closed (fig. 20) by governor pressure for at road speeds above 25 mph governor pressure is great enough to overcome its spring. The closing of this valve blocks off the large passage to the closed throttle downshift cushion valve. Main line pressure, therefore, is applied to the apply side of the low servo piston through the .107" drilled orifice. This provides for more gradual application of the low band, synchronizing it with the release of the high speed clutch.

Governor

The governor (fig. 21) which is driven by the output shaft of the transmission whenever the car is moving causes the transmission, when the selector lever is in automatic drive "D" range to be speed-conscious; i.e. it initiates the shift from low to high and from high to low.

The governor consists of a single plunger type valve and two sets of governor weights acting upon this valve. This construction actually provides a rotating pressure regulator. Two weights, producing a two stage pressure curve, are used to provide a pressure range, which will produce shifts at the desired speeds. The effect of centrifugal force on the combined weights affects the governor pressure at the lower speeds. Open the large outer weights hit their stops only the smaller-inner weights in combination with their springs determine pressure at the higher speeds. Oil under pressure is delivered from the transmission rear oil pump directly to the governor where it is regulated and directed to the shifter valve in the throttle valve body and to the forced downshift cushion valve which is in the main valve body.

Drive Clutch Relief Valve

In reverse and neutral, the low range drum and direct drive clutch piston revolve at high speeds. The high speed rotation creates sufficient centrifugal force in the oil remaining in the clutch apply chamber to partially engage the clutch. However, to prevent this, there is a clutch relief valve incorporated in the clutch drum. This relief valve consists of a steel ball that operates in a cavity and on a seat that is machined in the inner face of the clutch drum (fig. 22). A small hole leading from the center of the seat thru the outer face of the clutch drum provides an orifice. Staking around the edge of the cavity holds the steel ball in place.

In the clutch apply position, oil pressure holds the ball on its seat blocking off the orifice. When the clutch is in the released position, the centrifugal force of the rotating clutch assembly moves the ball off of its seat allowing any oil that may be trapped between the piston and dr