SECTION 4

REAR AXLE AND SUSPENSION

CONTENTS OF THIS SECTION

Figure Index
Rear Axle
Rear Axle Troubles and Remedies
Propeller Shaft and Universal Joints
Propeller Shaft and Universal Joints Troubles and Remedies
Rear Springs and Shackles
Rear Axle and Suspension Specifications
Assemby Manual

Figure Index

The rear axle and suspension is basically the same as in the 1955 passenger car. Many engineering innovations have been incorporated into the axle and suspension. However, the changes affect axle service procedure only. All procedures not outlined in thes supplement will be the same for 1956 as they were for 1955

The 1955 Chevrolet passenger car rear axle and suspension is of the semi-floating, hypoid gear hotchkiss drive type.

Differential Carrier

The hypoid drive pinion is of the over-hung type, mounted on pre-loaded taper roller bearings. Sealing the pinion shaft is accomplished at the front end by a spring loaded leather seal, bearing on the companion flange or rear universal joint rear yoke which is splined and bolted to the pinion shaft. The hypoid design ring gear is bolted to the arma-steel differential case which is mounted on preloaded barrel-roller bearings. Two differential side and pinion gears are of the revacycle design. The above units are mounted in a cast iron differential carrier, containing channels for the pinion bearings. Figure 1 shows a cross-section of this assembly.

Axle Housing

The differential carrier assembly is mounted into an all-welded rear axle housing which contains the rear axle shafts and bearings. The induction-hardened axle shafts are splined to the differential side gears in the differential case. The outer ends of the axle shafts support the weight of the rear of the vehicle on ball bearings. The bearings are pressed on the axle shaft and a soft steel retaining ring pressed on to aid in holding bearing position. The axle shaft bearings are held in the axle housing by bearing retainers. Axle shaft side thrust is absorbed by these bearings. Axle shaft sealing is accomplished by spring loaded neoprene seals between the inner and outer races of the ball bearings. An O-ring on the Fig 1A - Axle Shaft and Bearing Assembly bearing seals the outside diameter. Figure 2 shows a cross section of the axle shaft and bearing assembly.

Care, Maintenance and Adjustments

LUBRICANT

The lubricant level should be periodically checked and maintained at level of filler plug with a warm axle. See the lubrication section of this manual for lubricant recommendations. Lubricant Leaks Lubricant leaks should be checked for at the companion flange or rear universal joint rear yoke oil seal, sealing area of joint between differential carrier and axle housing, lubricant filler plug, and at axle shaft bearings. Correction of these leaks consists of replacing the defective seals or gaskets involved as described in this section.

Rear Wheel Bearings

The rear wheel bearings for 1956 Chevrolet passenger cars are the permanently lubricated type. The bearing is lubricated, then sealed on manufacture and needs no further lubrication for the life of the bearing. Previously, wheel bearings were lubricated with a splash type system within the axle housing.

U-BOLTS AND HUB NUTS

From a safety standpoint, axle housing to rear spring U-bolts and wheel hub nuts should be periodically inspected for secure installation.

REAR AXLE NOISE DIAGNOSIS

Mechanical failures of the rear axle are relatively simple to locate and correct. Noise in a rear axle is a little more difficult to diagnose and repair. One of the most essential parts of rear axle service is proper diagnosis.

One of the cardinal points of axle noise diagnosis is the fact that all rear axles are noisy to a certain degree. The action of transmitting the high engine torque through a 90° turn and reducing propeller shaft speed produces noise in rear axles. This point establishes the need for a line between normal and abnormal or unacceptable axle noises.

Slight axle noise heard only at a certain speed or under remote conditions must be considered normal. Axle noise tends to "peak" at varying speeds and the noise is in no way indicative of trouble in the axle.

If noise is present in an objectionable form, loud or at all speeds, an effort should be made to isolate the noise as being in one particular unit of the vehicle. Axle noise is often confused with other noises such as tire noise, transmission noise, propeller shaft vibration and universal joint noise. Isolation of the noise as in any one unit requires skill and experience. An attempt to eliminate a light noise may baffle even the best of diagnosticians. Such practices as raising tire pressure to eliminate tire noise, listening for the noise at varying speeds and on drive, float and coast, and under proper highway conditions, turning the steering wheel from left to right to detect wheel bearing noise, will aid even the beginner in detecting alleged axle noises. Axle noises fall into two categories, gear noise and bearing noise.

Gear Noise

Abnormal gear noise can be recognized since it produces a cycling pitch and will be very pronounced in the speed range at which it occurs, appearing under either "drive," "float" or "coast" conditions. Gear noise tends to peak in a narrow speed range or ranges, while bearing noise will tend to remain constant in pitch. Abnormal gear noise is rare and usually originates from the scoring of the ring gear and pinion teeth as a result of insufficient or improper lubricant in new assemblies. Side gears rarely give trouble as they are used only when the rear wheels travel at different speeds.

Bearing Noise

Defective bearings will always produce a rough whine that is constant in pitch and usually most noticeable under "drive" conditions. This fact will allow you to distinguish between bearing noise and gear noise.

1. Pinion bearing noise resulting from a bearing failure can be identified by a constant rough sound. Pinion bearings are rotating at a higher speed than differential side bearings or axle shaft bearings. This particular noise can be picked up best by testing the car on a smooth road (black top). However, care should be taken not to confuse tire noise with bearing or gear noise. If any doubt exists, tire treads should be examined for irregularities that would produce such noise.
2. Wheel bearing noise may be confused with rear axle noise. To differentiate between wheel bearings and rear axle, drive the vehicle on a smooth road at medium-low speed. With traffic permitting, turn the vehicle sharply right and left. If noise is caused by wheel bearings, it will increase in the turns because of the side loading. If noise cannot be isolated to front or rear wheel bearings, inspection will be necessary.
3. Side bearings will produce a constant rough noise of a slower nature than pinion bearings. Side bearing noise will not fluctuate in the above wheel bearing test.

1. Raise rear of vehicle and place stand jacks under rear axle housing.
2. Remove hub nuts and remove tire and wheel assembly.
3. Remove brake drum and gasket.
4. Remove four nuts and lock washers from bearing retaining bolts (on inside of axle flange).
5. Attach axle shaft puller J-5748 with slide hammer to hub bolts with three hub nuts and remove axle shaft and bearing assembly and gasket (fig. 3). Be careful not to disturb brake backing plate. NOTE: If bearing retainer and parking broke strut interfere, raise strut slightly with screw driver to obtain clearance.
6. Install bolt and nut to hold brake backing plate on axle housing.

INSPECTION

Inspect bearing for looseness, roughness or evidence of leakage at seal.

NOTE: When inspecting rear axle shaft bearings apply all of the load possible by hand as load is all important in bringing out bearing noise.

Inspect axle shaft for cracks, loose bolts or worn splines.

Repairs

Axle Shaft Bearing and/or Oil Seal-Replace

REPLACEMENT NOTE:
Bearing and axle shaft seal are serviced as an assembly. Replacement of either of both is the same as for Wheel Bearing Replacement in the 1955 passenger models. The new type bearing must be installed with the spring loaded lip toward the bearing retainer on the axle shaft fig. 1.

1. Using a hammer and chisel, nick the soft ring next to the bearing and remove the ring (fig. 4). NOTE: The ring need not be split, only nicked deep enough to allow removal.
2. Install press plate J-5741 between axle flange and bearing with the land of the plates against the bearing and inside the retainer. Install bolts in plates.
3. Fig. 4-Removing Lock Ring
4. Press bearing from shaft with press plate parting line (fig. 5) resting on press bed. CAUTION: Press plates must be supported at break as shown.
5. To replace oil seal, pry old seal out with screwdriver. Be careful not to damage bearing races. Install new seal, using Guide J-5747 (fig. 6). Tap seal in place with a plastic faced hammer.
6. Install new bearing or re-sealed old bearing, using Bearing Installer J-5746 (fig. 7). Bearing seats on shaft against shoulder. NOTE: Bearing retainer must be on axle shaft before bearing is installed.
7. Install new axle shaft bearing retaining ring on shaft, using J-5746 as above to seat the ring against the bearing. NOTE: Chamfered side of ring must go against bearing.

Axle Shaft-Replace

1. Insert five new special bolts and force heads down to the flange on new axle.
2. Peen end of shoulder on bolts into countersink around bolt holes in the flange, using Anvil and Hub Bolt Peening Tool J-554 (fig. 8). CAUTION: This peening operation is very important from a safety standpoint.
3. Install new bearing as outlined above.

1. Replace bearing "O" ring seal, Remove temporary nut and bolt holding brake backing plate in place.
2. Install new retainer gasket. Install axle shaft in housing using axle shaft tool J-5748 and slide hammer. Rotate shaft to align splines of shaft and differential side gear. Outer race of bearing must seat against shoulder in axle housing. NOTE: Parking brake strut may have to be raised slightly with a screwdriver to obtain clearance for bearing retainer.
3. Install nuts and lockwashers on bearing retainer bolts and tighten securely.
4. Install brake drum gasket, drum, wheel and hub nuts.
5. Lower vehicle to floor, and road test for a and noise.

REPLACE

1. Raise one rear corner of vehicle off floor and place jack stand under frame side rail. NOTE- This is to lock one rear wheel and obtain differential to body clearance. If operation is to be performed on a hoist, support frame on stand jacks, allow axle to drop for clearance and expand brake shoes on one wheel to lock wheel.
2. Check free wheel for freedom of rotation.
3. Separate rear universal joint, tape trunnion bearings to joint and lower rear of propeller shaft to floor.
4. Using an inch-pound torque wrench, J-5853, on the companion Range nut, rotate the pinion through several complete revolutions and record the torque required to keep the pinion turning (fig. 9). If old flange is to be installed, mark pinion and flange for reassembly in same relative position.
5. Holding drive flange with Companion Flange Holding Tool J-2637-A, remove companion flange nut and special washer (fig. 10). Discard nut.
6. Remove drive flange using Companion Flange Remover J-820-A bolted over holding tool J-2637-A (fig. 11). Pry old oil seal out, using a screwdriver or hammer and chisel.
7. Inspect drive flange for smooth oil seal surface or worn drive splines. Replace if necessary
8. On new flanges or old flanges with damaged deflectors, install new deflector, using tool J-5749 Deflector Installer (fig. 12).
9. Soak new seal in light engine oil for 10 minutes before installation, wipe O.D. of seal and coat O.D. of seal with a sealer, such as Permatex No. 3. Install new oil seal using driver J-5154, Output Shaft, Oil Seal Installer.
10. Install drive flange, aligning marks on pinion and flange if old flange is being used. If flange does not go on shaft easily, pull flange on shaft, using tool J-5780, Companion Flange Installer (fig. 13). The tool is threaded onto pinion shaft and large nut tightened to pull flange on shaft. Remove tool and install special washer and a new self-locking nut. CAUTION: Do not hammer fange on pinion shaft. To do so will damage ring gear and pinion. Tighten nut to remove end play and continue alternately tightening in small increments and checking preload torque with inch pound torque wrench until it is the same as recorded in step 4. NOTE: The position of the pinion and flange was previously marked so that reinstallation may be made with flange and pinion in some relative position.
11. Readjust brake if expanded above.
12. Lower vehicle to floor and road test for leaks and noise.

REAR AXLE ASSEMBLY REMOVAL

Major operations on this axle assembly may be performed without removing complete axle assembly from the vehicle. There may be occasions, however, when it will be necessary to remove the complete assembly as result of collision which may cause distortion of axle housing or axle shaft tubes. The following axle housing assembly removal, therefore, is to be used only when replacement of axle housing is necessary.

1. Raise vehicle from floor and support with stand jacks under frame side rails.
2. Remove rear wheels.
3. Remove two trunnion bearing "U" bolts from the rear yoke and split rear universal joint. NOTE: Tape the bearings to the trunnion.
4. Disconnect hand brake cable at equalizer and remove cables from cable clamps on frame.
5. Disconnect hydraulic brake line connection at rear axle housing.
6. Disconnect shock absorber eyes from anchor plates (fig.14)
7. While supporting axle assembly with hydraulic jack remove spring "U" bolts, nuts and anchor plate, and lower axle assembly to the floor.

1. Slide axle assembly under vehicle, raise into position and install "U" bolts, anchor plates and nuts, and tighten securely.
2. Replace shock absorber eyes to anchor plates.
3. Connect hydraulic brake line to connector at rear axle housing.
4. Connect hand brake cable and adjust. See "Brake Section."
5. Reassemble the rear universal joint, making sure "U" bolts are tightened securely.
6. Replace rear wheels and lower vehicle to floor.
7. Bleed brake lines at all four wheels. See "Brake Section."

The operations to follow are major service operations, but may be, as a result of axle construction, performed without removing axle assembly from the vehicle.

Differential Carrier

REMOVAL

1. Clean all dirt from area of differential carrier to axle housing joint.
2. Remove axle shaft as previously outlined. NOTE: Axle shaft need be pulled out only to clear differential side gears.
3. Remove two trunnion bearing "U" bolts from the rear universal joint and split joint. Lower propeller shaft to floor. NOTE: Tape the bearings to the trunnion.
4. Remove nuts and copper washers which attach differential carrier to the axle housing.
5. Place a drip pan under the carrier and slightly separate carrier and housing and allow lubricant to drain out. Remove differential carrier assembly (fig. 15).

1. Mount carrier assembly in a bench vise or holding fixture J-3289.
2. Mark bearing caps and carrier for reassembly in same position. Remove differential adjusting nut locks and bearing cap bolts.
3. Remove bearing caps and adjusting nuts by tapping on bosses of caps until free from dowels. CAUTION: Do not use screwdriver to pry cap off as this may damage machined face of cap.
4. Remove differential and ring gear assembly from the carrier housing. CAUTION: Exercise care that differential side bearing outer races are not dropped in removing assembly from carrier housing.
5. Remove differential pinion shaft screw and lockwasher and differential pinion shaft from differential case.
6. Remove differential pinions and side gears.
7. Hold companion flange from turning by installing holding tool J-2637-A and remove propeller shaft pinion flange nut and washer and remove differential (fig. 16). Remove flange by using tool J-820-A, bolted to flange with holding tool in place (fig. 17).
8. Remove pinion from carrier by tapping on front end with a soft faced hammer.
9. Remove pinion shaft oil seal, pinion front bearing and bearing spacer from carrier. NOTE: Some axles may have a 1 / 1 6" shim behind the spacer. This is a production item only and should be discarded.
10. Wash all parts in cleaning solvent. Thoroughly clean axle housing. Figure 18 shows the parts layout.

Inspect all bearing cups, races and rollers for scoring, chipping or evidence of excessive wear. On pinion bearing rollers, inspect large end of rollers for wear. This is where wear is most evident on taper roller bearings. NOTE: The rear axle pinion bearings are of the pre-loaded type, and the natural wear pattern is a frosted condition with occasional slight scratches on races or rollers. This does not indicate a defective bearing.

1. Inspect oil seal for evidence of wear or damage.
2. Inspect pinion splines and flange for evidence of excessive wear.
3. Inspect ring gear and pinion teeth for scoring, cracking or chipping.
4. Inspect differential case for cracks or scores on side gear and pinion gear thrust faces.
5. Check fit of differential side gears in case.
6. Check fit of side gear and axle shaft splines.
7. Inspect differential pinion shaft for scoring or evidence of excessive wear.
8. Inspect differential carrier for cracks or crossed threads on differential bearing caps and bosses.

Marking on Pinion

A number marked on the head of the pinion will indicate, in thousandths, the pinion mounting distance. These numbers will range from 39 to 51 (fig. 2) and will not include the period and zero, e.i. .0, prefixing a thousandths decimal type figure. In the procedure following, "Pinion and/or Bearing Replacement", an example is given on usage of this number.

Pinion and/or Bearing Replacement

Incorporated with the pinion number marking mentioned in previous paragraph, a different type of procedure has been adopted to determine pinion depth shim. A new tool, J-6266 Rear Axle Pinion Gauge, has been developed with this new procedure to facilitate service and obtain a more precise adjustment. The procedure applies to 1956 rear axles only.

1. Remove front and rear bearing cups with brass drift.
2. Install new bearing cups in carrier, using Front Wheel Bearing Inserter J-270-6 on front cup and tool J-270-14 on rear cup. Bearing cups should seal against shoulders (fig. 3) in differential.
3. Remove pinion rear bearing assembly using tool J-5740 press plate. Note size of shim removed from between bearing and gear.
4. If the original ring gear and pinion, pinion rear bearing assembly and differential carrier will all be reinstalled, the original shim or one of the same thickness may be used. If the ring gear and pinion, pinion rear bearing assembly or differential carrier are replaced, the correct thickness of the pinion depth shim may be determined as follows:
5. Lubricate pinion bearing cone and roller assemblies with gear lubricant. Position rear bearing in its cup in carrier. Rotate bearing several times to make sure it is seated.
6. Position gauge plate on rear bearing so that the chamfered corner is towards pinion side and top of differential as installed in the car. See figure 5.
7. While holding front cone and roller assembly in its cup with the clamp plate, insert the clamp screw through the gauge plate, both bearings and clamp plate. Secure with hex nut provided. Tighten sufficient amount to center bearings in cups only. Check to see that neither the gauge plate nor clamp plate touch the housing.
8. Oscillate gauge plate and bearings several times to be sure bearings are seated and then draw up hex nut until 20 inch-pounds of torque are required to oscillate plate and bearings. See figure 4. NOTE: A torque of 60 ft. lbs. may be required to tighten nut on clamp bolt in order to achieve simulated preload of pinion bearings after assembly. After tightening the clamp bolt nut, the 20 in. lb. torque is measured as shown in figure 4.
9. Install tool J-6266 body assembly across differential bores (figure 5). Plunger on body must point inward toward center of pinion rear bearing.
10. Mount a dial indicator KMO-30 on the tool body post with the indicator button on top of the tool plunger (see figure 5). Swing body so that plunger does not touch gauge plate, and set indicator dial at zero.
11. Slowly swing inner end of tool plunger across gauge plate until highest indicator reading is obtained. Record this measurement and recheck to see that it is correct.
12. Record factory marking on pinion. Subtract the measurement obtained with the tool from the marking on the pinion. The difference between these two figures determines the thickness of the pinion depth shim to be installed with the particular pinion and ring gear, and rear bearing and carrier being checked. Shims are available in six different thicknesses: .021", .024", .027", .030", .033", and .036". Use shim which is closest to the difference in measurements.

                          Example     Example    Example 
                          #1           #2         #3 
Pinion Marking            42           45         51 
Tool Marking              15           22         22 
Difference                27           23         29 
Proper Shim Thickness    .027         .024       .030 

1. Remove indicator, complete tool and pinion rear bearing cone assembly from carrier.
2. Position shim selected on pinion with shim tangs toward pinion gear head.

Differential Bearings - Replace

1. Install Differential Bearing Puller TR-278-R, making sure puller legs are fitted securely in case and retaining yoke is tight.
2. Tighten puller screw to remove bearings (fig. 25).
3. Place new bearing on hub with thick side of inner race toward case and drive in place with Differential Bearing Driver J-5768 (fig. 26). NOTE: This tool is counterbored and has pilot to assure proper installation and seating of bearing.

Ring Gear or Differential Case Replacement

1. Remove ring gear bolts and lockwashers.
2. With soft hammer tap ring gear off the case.
3. Install guide pins made from 3/8"-24 x 1 1/21" long cap-screws with heads cut off and ends slotted to ring gear (fig. 27).
4. Make sure back face of ring gear and face of case are free of dirt and burrs. Mount case on V blocks placed at side bearings and check face runout with a dial indicator. This should not exceed .003". Drop ring gear over pilot diameter of the case.
5. Install every other ring gear bolt and lockwasher, then draw them up evenly and snugly so that ring gear face is flush with face of case.
6. Remove guide pins and install remaining bolts. NOTE: All bolts should be tightened to 40-60 ft. lbs.

1. Mount carrier in a bench vise or holding fixture.
2. Lubricate pinion bearings with hypoid lubricant and install pinion in carrier.
3. Install pinion bearing spacer large end toward gear. A new spacer must be used.
4. Install front pinion bearing cone and roller assembly on pinion shaft.
5. Soak new oil seal for 10 minutes in light engine oil. Wipe O.D. at seal and coat with a sealer such as Permatex No. 3. Install new pinion shaft oil seal, using tool J-5154, Output Shaft Oil Seal Installer (fig. 28).
6. Install pinion flange and deflector assembly using Companion Flange Installer J-5780 and J-2637-A; Companion Flange Holding Tool (fig. 29). Install special washer and new special self-locking nut.
7. Tighten pinion flange nut, holding companion flange with J-2637-A holding tool, until torque required to turn pinion is 15 to 25 inch pounds
   fig. 30. This may require a nut torque of as high as 350 ft. lbs. Torque wrench J-5853 or a scale may be used to determine the preload. J-544-A scale should read 1 7/8 to 3 1/8 pounds when applied at an eight inch radius at notches in Companion Flange Holding Tool fig. 31 . CAUTION: Be certain there is no contact between oil deflector and carrier.
8. Install differential assembly in the carrier and install outer races and adjusting nuts. CAUTION: Carefully slide adjusting nuts alongside the bearing so that threads on nuts fit into threads in carrier.
9. Install bearing caps, aligning marks on cap with marks on carrier.
10. Install and tighten cap screws snugly.
11. Lubricate hubs of differential side gears with hypoid lubricant and install them into differential case.
12. Roll the two differential pinions into position and install pinion gear shaft and pinion gear shaft lock screw.

Ring Gear and Pinion Adjustment

1. Loosen right hand adjusting nut and tighten left hand adjusting nut using Differential Adjusting Wrench J-972 while turning ring gear (fig. 32). Continue tightening left hand nut until all lash is removed, then back off the left hand nut one notch to a locking position.
2. Tighten right hand nut to force left bearing firmly into contact with left adjusting nut. Then loosen the right nut and again tighten snugly against the bearing. NOTE: This position may be easily determined as the barrel rollers begin to move when contact is made.
3. Tighten right hand nut a minimum of one additional notch to maximum of two notches further to a locking position. This operation preloads the differential bearings.
4. With the dial indicator mounted as shown in Figure 33 the back lash should read .006" to .009" with .008" preferred for all 1956 passenger car rear axles.
5. Tighten bearing cap bolts to 115-135 ft. lbs. Recheck back lash and install both adjusting nut locks.

Pinion and Side Gear Repairs

Interference may be encountered on some models while pinion shaft is being removed. If pinion shaft will not clear ring gear, ring gear must be removed to avoid damaging teeth while pinion shaft is being removed.

Ring Gear and Pinion Contact Pattern

It is very important that tooth contact be tested before differential carrier assembly is installed. Allowable variations in the carrier or rear pinion may cause pinion to be too far in or out even when shimmed according to the shim chart. Thus, tooth contact must be tested and corrected as necessary or the gears may be noisy. This test may be performed as follows with the carrier assembly mounted in the holding fixture.

1. Thoroughly clean the ring gear and pinion teeth.
2. Paint ring gear teeth lightly and evenly with red lead and oil of a suitable consistency to produce a contact pattern.
3. Place a 1 1/8" deep socket on the companion flange nut and grasp firmly with a cloth to form a friction brake.
4. Using a 9/16" box wrench on the ring gear bolts, rock the ring gear back and forth, shifting bolt heads to develop a contact pattern line is called the "flank". The space between the on the teeth of the ring gear (fig. 34).

Inspect the contact pattern produced by the above procedure. Figure 35 shows the terminology used in analyzing contact patterns.

The large end of the tooth is called the "heel" and the small end the "toe". Also, the top of the tooth, which is the part above the pitch line, is called the "face", while the part below the pitch line is called the "flank". The space between the meshed teeth is referred to as "backlash."

Figure 36 shows correct and incorrect contact patterns. For illustrative purposes, "coast" side of gear contact is shown. Drive and cost side of gear teeth will have identical contact patterns.

Tooth pattern "A" provides the ideal bearing for quietness and long life. If the pattern shows a toe contact "B", it indicates not enough backlash.

To correct, move the ring gear away the pinion by loosening left-hand differential adjusting nut and tightening right-hand adjusting nut.

NOTE: Make adjustment one notch at a time, repeat check with red lead and continue adjustment until tooth contact appears as in "A". Backlash must remain within limits.

If the pattern shows a heel contact "C", it indicates too much backlash. Make correction as for "B", however, loosen right hand differential adjusting nut and tighten left hand adjusting nut to move ring gear toward pinion. Backlash must remain within limits.

If the pattern shows a high face contact "D", it indicates that the pinion is too far out, that is too far toward the front of the car.

To correct a pattern such as in "D", it will be necessary to install a thicker pinion shim as described under "Pinion and/or Bearing Replacement." A .003" thicker shim is recommended as a starting point. Continued changes may be necessary to obtain the correct setting.

If the pattern shows a flank contact "E", it indicates that the pinion is in too far. To correct, replace the pinion shim with one .003" thinner and a recheck contact pattern. Other changes may be necessary to obtain the correct pattern.

In making pinion adjustments, be sure backlash is correct before retesting with red lead for tooth pattern. Moving the pinion in reduces backlash and moving it out increases it.

NOTE: When proper tooth contact is obtained, wipe red lead from gears and carrier with cloth moistened with clean gasoline or kerosene.

Pour a liberal quantity of rear axle lubricant on gear and bearing and turn gears to work lubricant into all surfaces.

Installation

1. Clean out axle housing thoroughly and place new gasket over carrier mounting bolts.
2. Assemble differential carrier assembly to axle housing, install new copper washers and nuts and tighten securely.
3. Connect rear universal joint.
4. Road test for noise and leaks.

Symptom and Probable Cause
Probable Remedy

Excessive Backlash

a. Loose wheel bolts.
a. Tighten nuts securely. Make sure the tapered end of nut is toward wheel.

b. Worn universal joint.
b. Replace or overhaul joint.

c. Loose propeller shaft to pinion splines.
c. Replace worn parts.

d. Loose ring gear and pinion adjustment.
d. Adjust ring gear and pinion.

e. Worn differential gears or case.
e. Replace worn parts.

f. Worn axle shaft or differential gear splines.
f. Replace worn parts.

Klunking Noise in Axle or Vehicle Weight Shifts From Side to Side on Turns

a. Excessive end play in axle shafts.
a. Replace axle shaft bearings and or retainer.

Axle Noise on Drive

a. Ring gear and pinion adjustment too tight.
a. Readjust ring gear and pinion.

b. Pinion bearings rough.
b. Replace bearing and readjust ring gear and pinion.

Axle Noisy on Coast

a. Ring gear and pinion adjustment too loose.
a. Readjust rings gear and pinion.

b. Pinion bearings rough.
b. Replace bearing and readjust ring gear and pinion.

c. Excessive end play in pinion.
c. Adjust pinion bearings or replace bearings.

Axle Noisy on Both Drive and Coast

a. Pinion bearings rough.
a. Replace bearings and adjust ring gear and pinion.

b. Loose or damaged differential side bearings.
b. Replace or adjust differential side bearings.

c. Damaged axle shaft bearing.
c. Replace bearing.

d. Worn universal joint.
d. Replace worn parts.

e. Badly worn ring gear or pinion teeth.
e. Replace ring gear and pinion.

f. Pinion too deep in ring gear.
f. Adjust by shimming.

g. Loose or worn wheel bearings.
g. Replace wheel bearings.

Axle Lubricant Leaks

a. Axle shaft bearing seals leaking.
a. Replace axle shaft bearing seals and "0" rings.

b. Pinion shaft oil seal leaking.
b. Replace pinion shaft oil seal.

c. Differential carrier to housing gasket leaking.
c. Replace gasket

Propeller Shaft and Universal Joints

INDEX

General Description
Care and Maintenance
Service Operations
Removal
Repairs
Installation

General Description

The 1955 Chevrolet passenger vehicles utilize a tubular type propeller shaft in a hotchkiss type drive system. The two exposed universal joints are of the sealed roller bearing type, lubricated at assembly (fig. 37).

A sliding spline joint is placed at the front of the propeller shaft, between the front universal joint front yoke and the transmission output shaft, to compensate for changes in propeller shaft length. These changes are made necessary by up and down movement of the axle as well as the "wrapping" of the axle as torque loads are taken by the rear springs on starting and stopping.

Care and Maintenance

Propeller shaft maintenance is confined to the universal joints. These are lubricated at the factory and sealed. It is recommended that they be disassembled and lubricated every 25,000 miles.

Service Operations

REMOVAL

1. Split the rear universal joint by removing trunnion bearing "U" clamps. Tape bearings to keep them from becoming damaged.
2. Lower rear of propeller shaft to clear axle and pull to rear to remove assembly from vehicle.

REPAIRS

On universal joint:

1. Remove bearing lock ring from yoke.
2. Support shaft yoke in a bench vise or on a short length of 1 1/4" pipe.
3. Using soft drift and hammer, drive on one end of trunnion bearing just far enough to drive opposite bearing from yoke (fig. 38).
4. Support the other side of yoke in bench vise and drive other bearing out using brass drift on end of trunnion hub.
5. On front joint, remove trunnions from other yoke in a similar manner.
6. Remove trunnion.
7. Clean and inspect bearings. Re-lubricate with a high-melting point wheel bearing type grease.
8. Replace trunnion and press new or relubricated bearings into yokes and over trunnion hubs far enough to install lock rings.
9. Hold trunnion in one hand and tap yoke lightly to seat bearings against lock rings. NOTE: Replacement of rear axle drive flange is covered under the "Rear Axle Minor Service Operations" section of this manual.

INSTALLATION

1. Ascertain the condition of the slip joint seal trunnion hubs far enough to install lock in the transmission. Replace if necessary as rings. described in the transmission section of this manual.
2. Slip the front joint front yoke over the transmission output shaft.
3. Connect the rear universal joint by installing the two U bolts. Be certain the trunnions are properly seated in the rear axle drive flange.

PROPELLER SHAFT AND UNIVERSAL JOINTS

Symptom and Probable Cause
Probable Remedy

Excessive Vibration

a. Worm universal joint.
a. Replace worn parts.

b. Bent propeller shaft.
b. Replace bent shaft.

c. Universal joint yoke bearings worn.
c. Replace worn parts.

Excessive Backlash

a. Worn universal joints.
a. Replace worn parts.

b. Worn drive shaft or joint splines.
b. Replace worn parts.

Rear Spring Service Operations

Index

General Description
Care and Maintenance
Service Operations
Spring Leaf Inserts - Replace
Rear Spring, Rear Shackle
Removal
Inspection
Installation
Rear Spring
Removal
Inspection
Repairs
Installation
Rear Spring Hanger
Removal
Installation

General Description

The rear axle is attached to the frame through semi-elliptic leaf springs, 2 inches wide and 58 inches long. The springs have 4 channel-type leaves each, with the top leaf shot-peened for long life. The second and third leaves are equipped with wax-impregnated fabric inserts at the leaf-ends to assure uniform inter-leaf friction and quiet operation. Figure 39 shows a spring longitudinal-section with an insert riveted in place.

Inlox type torsion rubber bushings are used to mount the spring to the frame at the front ends. The springs are fastened to the axle housing at the spring seats by U-bolts. The springs are connected to the frame at the rear ends by rubberbushed shackles.

Care and Maintenance

No periodic maintenance is required on rear springs other than an inspection of shackle nuts, bushing bolts, and U-bolts for tightness of installation. Severity of service dictates the frequency of these inspections.

The front rubber bushings and rear rubber bushed shackles require no lubrication, as all movement is taken up in the rubber itself. The wax-impregnated spring leaf inserts do not require service other than replacement when worn through.

Service Operations

SPRING LEAF INSERTS-REPLACE

The spring leaf inserts may be replaced with the spring in the vehicle or removed and disassembled. The following procedure is for installed springs. The procedure for disassembled springs follows the same riveting process.

1. Raise rear of vehicle and support stand jacks under frame side rails to remove weight from rear springs.
2. Straighten tangs on the spring rebound clip lower halves and remove upper halves. Top clip may need only be raised for clearance.
3. Drill or chisel ends off of insert rivets. These are brass tubular rivets and are easily removed.
4. Remove old inserts and rivets. Drive a cold chisel between spring leaves if necessary to obtain clearance.
5. Install two new rivets in each new insert and install in place on spring (fig. 40).
6. Place a piece of strap iron approximately 1/8" x 1" x 3" between each rivet head and the spring leaf above the insert.
7. Lower vehicle to floor to close spring leaves and retain rivet anvils. Peen rivets, starting an even spread on the tubular rivets by using a large center punch. Finish peening with a ball peen hammer (fig. 41). CAUTION: Do not peen rivets too tightly or ends may be pinched or cut off.
8. Raise rear end of vehicle and remove riveting anvils.
9. Lower vehicle to floor and install rebound clip upper halves. Clinch clips securely and road test vehicle for noise.

Removal

1. Raise rear of body and frame assembly and adjust height to relieve tension or compression on rear spring rear shackles.
2. Remove two self-locking nuts from shackle pins and remove outer shackle plate from shackle.
3. Remove two outer rubber bushings from shackle pins. Body height may have to be adjusted to relieve pressure on bushings.
4. Move shackle inner plate and pin assembly toward frame until stopped by frame.
5. With a pry bar of at least 3/4" thickness rotate spring eye around hangar eye to position spring eye ahead of hangar eye and provide clearance for shackle removal (fig. 42).
6. Remove shackle inner plate and pin assembly.
7. Allow spring eye to seek its normal position.

Inspect the rubber bushings for excessive wear, damage or deterioration from the use of lubricants. Inspect the shackle plates and pins for cracks or defects. Replace necessary parts. Figure 43 shows the shackle disassembled.

Installation

1. Install rubber inner bushings on shackle pins, large end of bushing toward shackle inner plate.
2. With a pry bar of at least 3/4" thickness, rotate spring eye ahead of hangar eye and above frame to provide shackle installation clearance.
3. Install shackle, "humped" or convex side of plate up, into hangar eye and spring eye, sufficient distance to allow hangar to clear frame when spring is allowed to seek its normal position.
4. Allow spring eye to rotate down below hangar eye to normal position.
5. Install shackle inner plate and pins with bushings all the way into the shackle.
6. Install shackle outer rubber bushings over pins.
7. Install shackle outer plate, matching contour with inside shackle plate, with raised nut faces out away from shackle. Install nuts and leave loose.
8. Lower vehicle to floor and bounce several times to centralize bushings. Tighten shackle nuts to 25 to 30 ft. lbs. torque.
9. Install shock absorber lower eye to anchor pin and tighten nut securely.

Removal

1. Support frame side rails on stand jacks and remove spring shackle and new shock absorber as previously described.
2. Remove spring to axle U-bolts and shock absorber anchor plate and lower rear of spring to anchor.
3. Remove rear spring front bushing nut and bolt. Use a socket and extension on the head of the bolt to guide it through the frame side rail to prevent loss of the bolt inside the frame side rail.
4. Remove spring from vehicle.

Inspection

1. Inspect front eye bushing for wear, damage or deterioration.
2. Check spring center bolt for tightness.
3. Check spring leaf inserts for wear.
4. Check rear shackle bushings for wear, damage or deterioration.
5. Check for broken spring leaves.

Front Bushing Replacement

1. Place spring assembly in bench vise.
2. Install Rear Spring Front Bushing Remover and Installer J-136A in position (fig. 44) with adapter plug inside the bushing and pressure plate behind the spring eye. NOTE: End of bushing with flange on outer shell must be toward pressure or end plate of tool.
3. Turn center screw clockwise to remove the
4. Place large or flanged end of bushing on adapter slug and start bushing into spring front eye. Install tool J-136A and turn center screw clockwise to force bushing into spring. Flange of bushing should bottom on spring eye.

Spring Leaf Replacement

1. Place spring assembly in a bench vise and remove spring clips by bending tabs of lower half of clip.
2. Position spring in vise jaws, compressing leaves at center, next to center bolt.
3. File peened end of center bolt and remove center bolt nut. Open vise slowly and carefully to let spring assembly expand.
4. Replace broken leaf and replace any worn spring leaf inserts as previously described.
5. Align center holes in spring by means of a long drift and compress leaves in vise.
6. Remove drift from center hole and install new center bolt.
7. Install nut on center bolt and tighten securely and peen end of bolt to keep nut from loosening. If necessary, cut bolt to leave 3/16" for peening.
8. Align springs by tapping with a hammer and assemble spring clips, bending tabs of lower halves at clips over upper halves. NOTE: Spring clips should be bent sufficiently to maintain alignment, but not tight enough to bind spring action.

1. Raise front of spring and align bushing with hangar eye. Install through-bolt and install nut loosely.
2. Raise rear of spring, indexing center bolt head with hole in spring seat on axle. Install U-bolts, shock absorber anchor plate and U-bolt nuts. Tighten to 75-90 ft. lbs. torque.
3. Install rear shackle as previously described.
4. Lower vehicle to floor, bounce several times to centralize bushings and tighten front bushing nut to 60-90 ft. lbs. torque and rear shackle nuts to 25-30 ft. lbs. torque.

Removal

The rear spring hangars are riveted to the frame side rails. Should replacement be necessary, the following procedure should be followed.

1. Raise the vehicle and place on stand jacks.
2. Remove spring as previously outlined.
3. Drill a 3/16" hole through the four rivets which attach the hangar to the frame. Enlarge this hole with a 3/16" drill for depth of the rivet head only. Cut off the remainder of the rivet head with a sharp cold chisel.
4. Remove the hangar, then cut off the rivets flush with the frame side rail. CAUTION: Do not attempt to drive out the rivets without cutting them off, or the hole in the bottom plate of the side rail may be distorted.
5. Drive out the remaining portion of the rivet.

Installation

The new bracket should be arc-welded around all edges to the frame, using the old holes as locating points.

Rear Axle and Suspension Specifications

Item
Type                       Semi-Floating
Gears                      Hypoid
Ratio   
   Overdrive               4.11:1
   Conventional            3.70:1
   Powerglide               .005"-.008"
Backlash
Pinion
   Mounting                Overhung
   Adjustment              Shim and self locking pinion drive
                           flange nut and compressible bearing
                           spacer.  
Thrust                     Through taper roller, pinion brg's.
Bearings
   Front                   Timken cone and roller
   Rear                    Timken cone and roller
Differential Type          Two Pinion, Hyatt Barrel
Axle Shaft
   Type                    Wheel Drive Flange Integral with Shaft
   Minimum Diam.           63/64"
Axle Shaft Bearings        Ball type
Drove Torque               Rear Springs
Lubricant Capacity         3 1/2 Pints

SUSPENSION

Spring Type                              Semi-elliptical   
   No. leaves                            Four
   Inserts                               Wax-impregnated fabric
   Length                                58"
   Width                                 2"
   Bushings                              Rubber Type

PROPELLER SHAFT

Type                                     Open Hotchkiss
U Joints                                 Sealed Needle Bearing