SECTION 3

FRONT SUSPENSION

CONTENTS OF THIS SECTION

Figure Index
Front Suspension
Troubles and Remedies
Specifications
Assembly Manual

Front Suspension

Numerous engineering developments have been incorporated for 1956 in the front suspension. Service procedure in the 1955 Passenger Shop Manual remains unchanged for the 1956 model except for a change of specifications for the front suspension and for the addition of a new tool for front spring replacement.

The 1955 Chevrolet Passenger Car Models utilize the S.L.A. (short and long arms) type front suspension with spherical type joints connecting the control arms and steering knuckles (fig. 1).

This type of independent front suspension allows each wheel to move up and down to follow the contours of the road and produce a soft, level ride while retaining positive control of vehicle direction. The self-adjusting spherical joints use a minimum number of parts in the front suspension system and provide a stable front end that retains its stability over a long period of use.

The Chevrolet S.L.A. suspension uses the positive ride control of coil springs and direct acting shock absorbers. They are mounted between spring seats on the lower control arms and spring pockets in the front cross member.

The spherical joints have a ball seat of a phenolic fabric material which, when matched with the steel ball, produces long, trouble-free life. Neoprene seals retain the grease and prevent the entrance of moisture and dirt into the joint.

The inner ends of the upper and lower control arms are mounted on rubber torsion bushings which in turn are on forged steel shafts bolted to the front cross member. These bushings do not require lubrication, simplifying maintenance problems and eliminating the possibility of neglect caused bushing failure. The design and positioning of the control arms aids in controlling brake "dive" through a geometric weight transfer counteraction.

The front suspension system uses a forged steering knuckle that is connected directly to the upper and lower control arms at the spherical joints. This knuckle has the brake backing plat brake, brake shoe anchor-pin and steering arm bolted to it.

Rubber compression and rebound bumpers absorb the shock of excessive blows on the front suspension are mounted on the frame cross members, (rebound) and lower control arms, (compression).

Periodic maintenance of the front suspension includes lubrication of each of the four spherical joints every 1000 miles and lubrication and adjustment of the front wheel bearings every 10,000 miles.

FRONT WHEEL BEARINGS-ADJUST

The proper adjustment of the front wheel bearings is one of the important service operations that has a definite bearing on safety. A car with improperly adjusted front wheel bearings lacks steering stability, has a tendency to wander or shimmy and causes excessive tire wear. In an effort to provide for more accurate adjustments the spindles are drilled both vertically and horizontally and the adjusting nuts are slotted on all six sides.

1. Jack up front end of vehicle. Remove hub cap and dust cap. Remove cotter pin from end of spindle.
2. Tighten spindle nut to 33 ft. lbs. torque while rotating wheel.
3. Check the location of a slot in the nut with reference to a hole in the spindle. If a slot in the nut lines up with either the vertical or horizontal holes in the spindle (see Fig. 2), back off the nut ( 1/6 turn) until the next slot in the nut lines up with the same hole in the spindle and insert cotter pin (see B, Fig. 2).
4. If, when the spindle nut is tightened to 33 foot pounds, the slot in the nut has passed beyond the vertical or horizontal holes in the spindle (see C, Fig. 2), back off the nut a sufficient amount (less than 1/6 turn) to line up the second next slot in nut and the other hole in the spindle.
5. To illustrate this point the slots in the nut are indicated 1, 2 and 3 (see D, Fig. 2). If the slot marked 1 on the nut is slightly beyond the vertical hole in the spindle, the nut should be backed off until the slot marked 3 is in line with the horizontal hole in the spindle. It will be noted that the nut has been backed off slightly less than 1/6 turn. NOTE: Front wheel bearings should never be set up on the loose side as such an adjustment does not bring the balls and races into proper contact. Final adjustment should have the nut backed off 1/12 to 1/6 turn, 1/2 to I flat of nut.
6. Spin the wheel to make sure that it rolls freely. Properly lock the cotter pin by spreading the end and bending it around. Install the dust cap and hub cap or wheel disc.
7. Remove jack.

A front end alignment is the process of checking or adjusting all the inter-related steering components of the front suspension system. Correct alignment must be maintained in order to assure ease and stability of steering and satisfactory tire life.

There are five components of steering geometry, all inter-related, but each having a specific purpose. These components, steering axis inclination, caster, camber, toe-in and cornering wheel relationship should be checked at regular intervals, particularly if the front suspension unit has been subjected to heavy impacts.

The following paragraphs explain front end alignment terminology.

Caster - is the angle in side elevation between the steering axis (centerline between spherical joints) and the vertical. It is considered positive when the steering axis is inclined rearward. The 1955 Chevrolet front suspension, featuring brake-dive control, has a variable caster angle, varying with vehicle height. Thus, it is important that the vehicle be at curb weight when caster angle is measured.

Camber - is the amount in degrees that the front wheels are tilted outward at the top from a vertical position (fig. 3).

When a wheel is tilted too far out at the top, hard steering or wander will be experienced and tires will show excessive wear on outside shoulders. A wheel that is tilted too far in at the top will result in excessive tire wear on the inner shoulders. Unequal camber may result in unstable steering wandering or unusual tire wear.

Toe-In - is the amount in fractions of an inch that the wheels are closer together at the extreme front of the tire than at the rear. The purpose of the toe-in is to provide parallel rolling of the front wheels when the vehicle is moving, to stabilize steering and prevent side slipping and excessive wear of tires. A slight amount of positive toe-in, measured statically with the vehicle at rest, is required to offset the small deflections due to rolling resistance and brake application which tend to turn the wheels outward.

Cornering Wheel Relationship - is the relative alignment as the front wheels are turned right or left. The governing factors are the length and angularity of the steering arms and linkage.

The front wheels, when the vehicle is making a turn, are not on the same radial line through the center around which the vehicle is turning. Because of this, it is necessary for the front wheels to assume a toed-out position when rounding curves. This puts each wheel axis on a radial line through the center of the turn, providing rolling rather than sliding action.

Steering Axis Inclination - is the angle in front elevation between the steering axis and the vertical (fig. 3). The steering axis, an imaginary center line between the upper and lower spherical joints on the 1955 Chevrolet front suspension, is the axis about which the wheel pivots as it is turned for control of vehicle direction. This inclination establishes the pivot point for turning the wheels near the center of the area of tie rod contact, contributing to steering ease.

Alignment Preliminary Steps

There are several different types of front end alignment machines, all of which outline proper procedure for checking the factors of front end alignment. The instructions furnished by each manufacturer for the operation of his particular machine should be followed. Regardless of type of equipment used, all checks must be made with the vehicle level and with the curb weight of the vehicle on the wheels.

Steering complaints are not always the result of improper front wheel alignment. Therefore, it is recommended that the following factors be checked and corrected if necessary prior to placing the vehicle on the front end machine.

1. Loose or improperly adjusted steering gear.
2. Steering gear housing loose at frame.
3. Play or excessive wear in spherical joints.
4. Loose tie rod or steering connections.
5. Improper front spring heights.
6. Underinflated tires.
7. Unbalanced tires.
8. Wheel bearings improperly adjusted.
9. Shock absorbers not operating properly.

The caster and camber adjustments are made by means of shims between the upper control arm inner support shaft and the support bracket attached to the frame side rail. Shims may be changed at either the front of the shaft or the rear of the shaft to change caster or at both points equally to change camber.

The addition of shims at the front bolt or removal of shims at the rear bolt will decrease positive caster. A 1/32" shim difference, one shim, will change caster 1/4. Adding shims at both front and rear of support shaft will decrease positive camber. A 1/32" shim change will move camber 1/6.

The procedure for adjustment is to loosen the upper support shaft to bracket bolts, add or remove shims as required and retighten the bolts (fig. 4).

NOTE: Both caster and camber can be adjusted in one operation.

Caster should be 0 plus or minus 1/2 and camber should be 1/2 plus or minus 1/2.

Steering Axis Inclination -Adjust

From the definitions of "steering axis inclination" and "camber", one being the inward tilt of the knuckle and the other the outward tilt of the wheels, it is evident that one cannot be corrected without changing the other. The correct steering axis inclination should be 3 1/2 plus or minus 1/2. This figure is comparable to kingpin inclination on suspensions utilizing kingpins.

The addition of camber and steering axis inclination should be 4 1/2. If not within these limits, the knuckle is bent and should be replaced. If a new knuckle is installed, caster, camber and toe-in must be readjusted.

Toe-In Adjust

Toe-in, which should be 1/8" to 3/16" can be adjusted by loosening the clamp bolts at each end of each tie rod and turning each tie rod to increase or decrease its length as necessary, until proper toe-in is secured and the steering gear is on the high point for straight ahead vehicle travel.

The procedure to be used is dependent upon the type of equipment being used. If equipment measuring the toe-in of each wheel individually is available, the following procedure should be used.

1. Set steering gear on high point, with mark on top end of steering mainshaft in a vertical position and steering wheel positioned for straight ahead driving.
2. Loosen the clamp bolt at each end of each tie rod and adjust them individually to 1/16" to 3/32" toe-in of each wheel (fig. 5).
3. Position the tie rod clamp bosses below the tie rod to avoid frame interference and tighten the clamps securely.

If a tram gauge is utilized, the following procedure should be used.

1. Set the front wheels in a straight ahead position.
2. Loosen the clamp bolts on one tie rod and adjust for 1/8" to 3/16" toe-in.
3. Loosen the other tie-rod clamp bolts. Turn both tie rods the same amount and in the same direction to place the steering gear on its high point and position the steering wheel for straight ahead driving.
4. Position the tie rod clamp bosses below the tie rods and tighten securely.

Cornering Wheel Relationship, or toe-out on turns, is determined by the angle of the steering arms. If, when checking, toe-out does not fall within the limits given in the specifications, it will be necessary to replace the steering arm on the wheel side that does not come within limits.

HUB AND DRUM ASSEMBLY

Removal

1. Remove hub caps, loosen wheel to hub bolt nuts, raise vehicle from floor, place on stand jacks and remove wheels.
2. Remove hub grease cap, cotter pin, spindle nut, spindle washer and remove drum and hub assembly. NOTE: In some cases it may be necessary to back off the brake adjustment because of scored drums or badly worn linings holding drum on.
3. Remove outer bearing from hub with fingers. The inner bearing will remain in the hub and may be removed by prying out the inner bearing felt seal assembly. Discard seal.
4. Wash all parts thoroughly in cleaning solvent.

Inspection

1. Check all bearings for cracked bearing separaters or worn or pitted balls.
2. Check bearing race for cracks or pitting.
3. Check brake drum for out of round or scored condition.
4. Check bearing outer race for looseness in hub.

Bearing Races - Replacement

1. Insert Front Wheel Bearing Cup Remover K-224 through hub, indexing end of tool with notches in hub shoulder behind bearing cup.
2. Tap lightly on cup through each notch to remove cup from hub.
3. Install new bearing cup in hub using K-463A Bearing Cup Inserter (fig. 6).
4. Make sure that cup is not cocked and that it is fully seated against shoulder in hub.

Brake Drum - Replacement

The brake drum is held to the hub by three rivets which must be removed to replace the brake drum.

1. Cut heads from three rivets which retain drum to hub. Drilling through upset end of rivet will permit cutting them without distorting holes. A sharp cold chisel should be used in this operation and care exercised to avoid distorting rivet holes. Drive rivets from drum and hub using punch and remove drum from hub bolts.
2. Remove brake drum gasket from hub and clean gasket surface on hub thoroughly.
3. Install new brake drum gasket and brake drum over hub bolts and insert three new rivets through rivet holes in hub, gasket and drum.
4. Support heads of rivets and peen ends securely.

Wheel Hub - Replacement

1. Remove inner and outer bearing cups.
2. Remove three rivets retaining brake drum to wheel hub and remove brake drum.
3. When installing a new hub it is necessary to install new bolts, rivets and gasket.
4. Install new hub bolts. The end of the shoulder on the hub bolts should be peened into the countersink around the bolt holes in the hub flange, using J-554 Peening Tool and Anvil (fig. 7). NOTE: Shoulder of bolts must be peened into hub countersink approximately 1/16" before assembling drum.
5. Install new brake drum gasket and brake drum over hub bolts.
6. Install three new rivets through rivet holes in hub flange gasket and drum and, supporting rivet heads, peen ends securely.
7. Install inner and outer bearing cups into hub using K-463-A, Bearing Cup Inserter Set.

1. Hand pack both inner and outer bearings, using a high melting point wheel bearing lubricant.
2. Place inner bearing in hub, then install a new inner bearing felt seal assembly. Side of seal with bent lugs should be up as installed, or toward center of the vehicle.
3. Using a piece of fine sandpaper, lightly sand the inside braking surface of brake drum to insure a clean surface and proper brake operation.
4. Carefully posit-on hub on spindle.
5. Install outer bearing, pressing it firmly into the hub by hand.
6. Install spindle washer and spindle nut. Draw spindle nut up snug and adjust bearings.

In cases of vehicle riding height complaints, a coil spring height check will show if the front suspension is at the right height.

1. Position car on smooth, level floor.
2. Bounce and rock the car several times and allow it to settle to a normal height.
3. Measure the distance from the floor to the center of the front inner pivot of lower control arm (fig. 8). Record this measurement.
4. Measure the distance from the floor to the lower face of the lower steering knuckle boss for the spherical joint on the same side of the vehicle. Record this measurement.
5. The difference between these two measurements should be 2 1/2" to 3", with the vehicle at curb weight.
6. Measure the opposite side of the vehicle in a similar manner. It is essential that the two differences be close.
7. To correct the height, springs must be replaced. These springs do not have flat ends and shims should not be used.

Removal

1. Remove front shock absorber on the side spring to be replaced as outlined under "Front Shock Absorber-Removal" in Section 2.
2. Raise the front end of the car off the floor and place stand jacks beneath frame side rails, Lower car until weight is carried on stand jacks.
3. Remove tire and wheel assembly. NOTE: It is important that wheel and tire assembly be removed to avoid damage to spherical joints during spring operations.
4. Break loose the four lower control arm cross shaft bushing bolts.
5. Install Spring Compressor J-6318 fig. 2A through shock absorber mounting hole in front cross member and through spring. Install nut washer and thrust bearing on Compressor shaft to keep Compressor from falling back through.
6. Index Cross Shaft J-6318 (see figure 1) through eye in Compressor. Attach Cross Shaft to shock absorber pivot bar bolt holes in bottom of lower control arm. Use bolts from pivot bar, tighten securely.
7. Tighten upper Compressor nut to slightly compress spring.
8. Remove lower spherical joint cotter pin and nut. Loosen the stud by hammering on the side of the steering knuckle joint boss, backing up the steering knuckle with a heavy hammer.
9. Remove upper spherical joint stud from knuckle in a similar manner, and hang drum and knuckle assembly without loading brake hose.
10. Remove four lower control arm inner shaft to cross member nuts and bolts.
11. Unscrew spring compressor nut and remove spring and lower control arm from vehicle.

NOTE: On some models the generator may have to be loosened, then raised in order to compress spring compressor.

Installation

1. Install spring on shaft of Compressor. Index Compressor shaft through upper shock absorber hole and tighten nut on shaft to barely contact spring with cross member.
2. Rotate spring to be certain it fits the helical seats in lower control arm and cross member.
3. Tighten spring Compressor to draw up to compressed height.
4. Install nuts and bolts fastening lower control arm to cross member and tighten securely.
5. Install new rubber seals on joint stud.
6. Install knuckle and brake assembly to control arms, releasing spring compressor slightly to allow spherical joint studs to enter knuckle bosses.
7. Install spherical joint stud nuts, tighten securely and install cotter pins.
8. Remove spring compressor and install shock absorber as outlined under "Front Shock Absorber-Installation" in Section 2, 1955 Passenger Manual.
9. Install wheel and lower vehicle to floor.

Lower Control Arm Spherical Joint, Cross Shaft Or Bushings

When replacing the lower control arm, spherical joint, shaft or shaft bushings, it is necessary to remove the control arm assembly from the vehicle.

Removal

Removal of lower control arm is covered under "Front Spring Removal."

Spherical Joint Inspection

The lower control arm spherical joint should be replaced whenever excessive wear is indicated in the upper joint inspection.

NOTE: The lower control arm spherical joint stud is a loose fit in the assembly when not connected to the steering knuckle.

Spherical Joint Replacement

1. Chisel or drill heads of rivets retaining spherical joint to control arm and drive out rivets.
2. Discard spherical joint and seal.
3. Install new joint with flange against underside 'de of control arm and retain joint in place with special bolts and nuts supplied with new joint. CAUTION: Use only alloy bolts supplied for this operation.
4. Tighten nuts to 10-12 ft. lbs.

Cross Shaft and/or Bushing Replacement

1. Remove bolt, lockwasher and collar from each end of cross shaft.
2. Install three piece spacer of J-5888 Bushing Remover and Installer in control arm as shown in fig. 11.
3. Thread a 7/16-20 cap screw (furnished with J-5888) to the bottom of the threads in the one end of the cross shaft.
4. Support control arm in an arbor press, on the support detail of J-5888 as shown in fig. 11. CAUTION: Be certain bushing flange does not contact support.
5. Press on cap screw until bushing is free of control arm. Discard bushing.
6. Remove cap screw, insert cap screw in other end of shaft. Invert control arm on support (fig. 12). Again be certain bushing flange does not contact support.
7. Press on cap screw until bushing is free of control arm. Discard bushing.

Installation - Bushing

1. Coat outside sleeve of bushing sparingly with a lubricant. CAUTION: Avoid getting lubricant on rubber bushing.
2. With cross shaft in control arm and three piece spacer in place, place control arm on support. Hand start bushing into control arm and over end of cross shaft. CAUTION: End of shaft with greatest distance from end of shaft to bolt holes should be toward front of control arm.
3. Install collar of J-5888 over bushing. Be certain three-piece spacer is not over-lapping bushing holes in control arm. Press bushing into control arm until flange contacts control arm (fig. 13).
4. Invert arm in press and repeat the process on the other bushing. After installation, cross shaft should be able to be rotated by hand.
5. Install collar, lockwasher and cap screw in each end of cross shaft. Do not tighten.

Installation - Control Arm

Lower control arm installation is covered under "Front Spring-Installation." After installing control arm on vehicle, bounce front of vehicle to centralize bushings and tighten bushing collar bolts to 45-55 lbs. ft.

Upper Control Arm Spherical Joint, Cross Shaft Or Bushings

Removal

1. Support vehicle weight at outer end of lower control arm.
2. Remove wheel and tire assembly.
3. Remove cotter pin and nut from upper control arm ball stud.
4. Loosen the stud by hammering on side of the steering knuckle joint boss, backing up knuckle with a heavy hammer.
5. Remove two nuts retaining upper control arm shaft to front cross member. Note number of shims at each bolt.
6. Remove upper control arm from vehicle.

Spherical Joint Inspection

The upper spherical joint is checked for wear by checking the torque required to rotate the ball stud in the assembly. Install a stud nut on the stud and measure the torque required to turn the stud in the assembly with a torque wrench. This should be a minimum of 2 ft. lbs. If excessive wear is indicated in upper joint, both upper and lower joints should be replaced. If a tight joint is suspected, 15 ft. lbs. is the maximum allowable torque with joint well lubricated.

NOTE: This inspection does not necessitate upper control arm removal. Follow the upper arm removal procedure through Step 4 and raise the arm for the check.

Spherical Joint Replacement

The upper control arm spherical joint is replaced as outlined for lower control arm, except that flange of joint is installed on topside of upper control arm and a shield is installed around joint on underside of control arm.

Cross Shaft and/or Bushing Replacement

1. Remove cap screws, lock washers and collars from both ends of cross shaft.
2. Install a 3/8-24 cap screw (furnished with J-5888) in one end of cross shaft.
3. Support control arm in an arbor press on support of J-5888 as shown in fig. 14. CAUTION: Be certain flange of bushing does not contact support.
4. Press out bushing, invert control arm and repeat process on other bushing. Discard bushings.
5. Remove cap screw from cross shaft.
6. Install arm in an arbor press with the one piece spacer of J-5888 in place and press in one bushing, using the Bushing Collar of J-5888 as shown in fig. 15.
7. Install cross shaft in arm, invert in press and, with spacer of J-5888 in place, press in second bushing as above.
8. Cross shaft should be able to be turned by hand.
9. Install collar, lockwasher and cap screw in ends of cross shaft. Do not tighten.
10. Install collar, lockwasher and cap screw in ends of cross shaft. Do not tighten.

Installation

1. Install upper control arm to vehicle.
2. Install two nuts and bolts retaining upper control arm shaft to front cross member. Install same number of shims as removed at each bolt.
3. Install new rubber seal on joint stud.
4. Install ball stud through knuckle, install nut, tighten securely and install cotter pin.
5. Install wheel and tire assembly.
6. Lower vehicle to floor.
7. Bounce front end of vehicle to centralize bushings and tighten bushing collar bolts to 35-40 lbs. ft.

FRONT AXLE AND WHEEL ALIGNMENT

Symptom and Probable Cause
Probable Remedy

Hard Steering

a. Lack of lubrication.
a. Lubricate chassis and steering gear.

b. Tight spherical joints.
b. If not corrected by lubrication, replace joints.

c. Underinflated tires.
c. Inflate tires to recommended pressure.

d. Improper front end alignment.
d. Adjust front end alignment.

e. Improper steering gear adjustment.
e. Adjust steering gear.

f. Tie rod ends out of alignment.
f. Align tie rod ends with ball studs.

Front Wheel Shimmy

a. Underinflated tires.
a. Inflate tires to recommended pressure.

b. Broken or loose wheel bearings.
b. Replace or adjust wheel bearings.

c. Improper toe.
c. Adjust toe.

d. Worn spherical joints.
d. Replace joints.

e. Improper caster.
e. Adjust caster.

f. Unbalanced wheels.
f. Balance wheel and tire assemblies.

g. Steering gear loose.
g. Adjust steering gear.

h. Tie rod ball loose.
h. Replace tie rod end.

Road Wander

a. Underinflated tires.
a. Inflate tires to recommended pressure.

b. Lack of lubrication.
b. Lubricate chassis and steering gear.

c. Tight steering gear.
c. Adjust steering gear.

d. Improper toe-in.
d. Adjust toe-in.

e. Improper caster and camber.
e. Adjust caster and camber.

f. Worn tie rod ends.
f. Replace tie rod ends.

g. Loose relay rod.
g. Adjust relay rod joint.

Wheel tramp

a. Wheel assembly out of balance.
a. Clean wheel and balance assembly.

b. Blister or bump on tire.
b. Replace or repair tire.

c. Improper shock absorber action.
c. Replace shock absorber.

Excessive or Uneven Tire Wear

a. Underinflated tires.
a. Inflate tires to recommended pressure.

b. Improper camber.
b. Adjust camber.

c. Improper caster.
c. Adjust caster.

d. Improper toe-in.
d. Adjust toe-in.

e. Wheels out of balance.
e. Balance wheels.

f. High speed cornering.
f. Instruct driver.

g. Brakes dragging.
g. Adjust brakes.

Front Suspension Specifications

Caster Degrees.....................  + 1/2 deg to  + 1 1/2 deg 
Camber-Degrees....................................... 0 to 1/2
Steering Axis Inclination - Degrees............. 3 1/2 - 4 1/2
Toe-In-Inches.................................... 1/8" - 3/16"
Cornering Wheel Relationship
    (Toe-Out on Turns)
         Outside Wheel-Degrees.................  18 deg to 10"
         Inside Wheel Degrees ......................... 20 deg 

Reading Height - Front Springs

Measure from lower face of knuckle lower spherical joint boss to floor and center of lower control arm inner front bushing to floor.

Difference should be............................. 2 1/2" to 3"

TORQUE SPECIFICATIONS
 
Tie Rod Clamp Bolt Nut - 8-12 Ft. Lbs.

 Spindle Nut - See Front Wheel Bearings-Adjust

 Replacement Joint Bolts - 10-12 Ft. Lbs.


Assembly Manual 






Front End Suspension

Upper and Lower Control Arm

Steering Knuckle and Wheel Hub

Front Shock Absorber and Spring

Front Suspension Geometry

Front Spring Color Code