1972 C3 Corvette Rear Suspension Diagram

At this stage, the frame has been inspected, repaired, and finished. All of the light rust damage has been repaired. Any accident damage or rust that has eaten through the frame has been cut out. New parts have been welded into place by a professional Corvette repair shop. This is the perfect time to install refurbished or rebuilt components.

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This Tech Tip is From the Full Book  "HOW TO RESTORE YOUR C3 CORVETTE: 1968-1982". For a comprehensive guide on this entire subject you can visit this link:

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Place the frame in a low-traffic and well-lit area so it can be safely reassembled. Placing it on a large piece of non-shag gray (or any light color) carpet makes it easier to locate dropped parts. The carpet stops parts from bouncing under a table or into a small crevice. Place the frame on four safety stands that are sturdy and protected with pieces of cardboard.

Set up several large tables so assembly parts can be laid out in their correct order. This saves a lot of time during the reassembly process when trying to locate the next part to install onto the frame.

Front Suspension

The front suspension is the perfect place to start reassembling the foundation of your C3. Simply reverse the disassembly procedure discussed in Chapter 6. Tubular upper and lower aftermarket control arms are available from Corvette suppliers such as Van Steel. These parts reduce the unsprung weight of your front suspension and are just as strong as the stamped-steel factory parts. However, if you are just going to use your car for cruising and not racing the factory parts work very well.

Component Evaluation

This is a good time to refurbish or replace the steel control arms. Several well-known Corvette specialty shops offer like-new components at a competitive price that includes a warranty. Each part is cleaned, inspected for cracks, aligned, and powdercoated. New ball joints with rubber or polyurethane bushings are included in the rebuild process. These control arms come ready for installation. In my opinion, this is money well spent.

A C3 Corvette's differential is the centerpiece of the car's rear suspension. The differential is solidly mounted to the frame and is connected to the engine with a driveshaft. The transverse leaf spring bolts to the differential and is connected to the rear suspension trailing arms. All of these components should be evaluated, inspected, and repaired or replaced as necessary.

Now that the frame has been returned to your work area, reconfirm your factory frame measurements. To take the desired measurements, refer to the top right photo on page 87. The frame is light enough for two people to carry it to your work area for assembly.

This frame has been carefully placed on four safety stands and four large pieces of cardboard to protect the frame from any scratches. The large gray carpet remnant makes the reassembly process more comfortable and dropped parts are more easily found. Start gathering various bits and pieces, such as small bolts and brake and fuel lines, and place them in your work area.

Van Steel uses this square piece of aluminum cut to the proper specification to measure the distance between the two upper control arm brackets. The correct measurement is 26-3/8 inches. This is an important area to reinspect before you start installing your parts because the crosspiece that runs under the engine is prone to bending. Any mismeasurement makes it difficult to align the chassis correctly. The two rear lower control arm attachments must also be securely welded to the frame.

Your completed front suspension should look like this unit, which is installed on a 1980 Corvette. The anti-roll bar has not been installed and is the only missing part in this photo. The upper and lower control arms secure the coil spring. The new shock runs up the middle of the spring and is attached to the upper frame and the lower control arm. This car received a new steering knuckle, wheel bearings, and brake rotor.

The suspension undergoes a lot of stress, and this is the perfect time to rebuild or refurbish these parts before they are reinstalled. Many Corvette part suppliers sell complete suspension components that have been refurbished. They start the process by disassembling the old parts. The ball joint rivet heads are ground down flush and then chiseled out of the upper control arm with an air chisel.

After the bushings, ball joint, and steel shaft have been removed from the control arm, the shop inspects for cracks or other damage. If it meets specifications, it is shot peened to remove all accumulated grime and paint. This process is the best for identifying any cracks. The parts are then sent to the powdercoating shop to have their surfaces covered and protected. Shown here are a front lower control arm (front) and a rear trailing arm (back). Send as many parts as possible to the powdercoating shop in order to get the most for your money.

Gather all necessary parts that need to be installed onto the frame. Large tables are an excellent place to organize these pieces. This helps keep critical parts within easy reach.

Organize and inventory your parts before starting the assembly process. Lay out the critical components of your front suspension assembly as shown. This includes the upper and lower control arms, steering knuckle with brake rotor, installed wheel bearings, and coil spring. The dust caps are used to cover and protect the front wheel bearings.

However, if this is not in your budget, at a minimum you need to replace the ball joints and the rubber bushings.

This is also a good time to steam clean the parts and repaint or powdercoat before reinstallation.

Upper Control Arms

The upper control arms are used to adjust the car's front suspension caster and camber settings. This is done with thin shims inserted between the frame and the control arm's steel shaft. Do not tighten the two bolts that secure the upper control arm's rubber or poly bushings until the car is ready to be driven. The suspension must have time to settle on the springs before these bolts are tightened. This is a very important step to remember.

After the powdercoating has been applied to the control arm, it is returned to the assembly area. A new ball joint is installed and the steel shaft receives new rubber or poly bushings. A piece of wood or a half piece of pipe is placed on the inside of the control arm to keep the arm from bending while the bushings are being pressed into the control arm.

Two 3/8-24 x 7/8-inch bolts secure the steel shafts that are included on the refurbished upper control arms. The upper control arm bushings are now fitted with new rubber units. The lower control arm has also received new ball joints and new bushings. Both are now ready to be installed into the frame.

Step-1: Install Bolts

Two 7/16-13 x 21⁄4-inch bolts secure the upper control arm to the frame. Each bolt has a wedge near the head (arrow) that prevents it from moving once the suspension has been mounted.

Place a long fl at bar onto the head of each bolt and hit the bar with enough force to push the head flush against the frame. Don't be afraid to hit the heads forcibly because they are designed for this procedure. Once the bolts have been secured, install the upper control arm bracket.

Step-2: Install Upper Control Arm Bracket

Slide the control arm steel bracket through the two bolts and thread on the 11/16-inch nuts. Do not tighten the nuts yet. The upper control arm rubber bushing bolts should remain loose until the project has been completed. When installing the control arm, don't forget to replace the factory alignment shims (two in the rear and one in the front). Tighten the 11/16-inch locking nuts to 50 ft-lbs.

Lower Control Arms

As with the top control arm, the lower ball joint is bolted to the steering knuckle with one nut. The antiroll bar end is attached to the lower control arm with a link. A large rubber bumper is attached to the lower control arm. This bumper is designed to hit the lower frame rail if the suspension is fully compressed; this helps avoid damaging any suspension components if a bump is taken too hard. This simple but effective design is very robust and gives long, trouble-free service when maintained properly.

Step-1: Install Bolts

The lower control arm includes a steel shaft and is attached with two 7/16-20 x 1.-inch bolts at each end of the arm. The shaft is fitted with rubber bushings. Use a 5/8-inch wrench to snug these bolts. Use the same procedure on these bolts as discussed in step 2 above. By leaving them just snug, the arm is able to move up and down freely during the next steps.

Step-2: Install Bolt Screw into Retainer

A small retainer at the front of the lower frame holds both front lower control arm bolts in place. The bolts screw into this retainer and you must take extra care not to strip the threads when you secure the steel shaft to the frame. Torque the two front bolts to 70 ft-lbs with a 5/8-inch socket.

Step-3: Install Nut on Control Arm

A 9/16x18x25⁄32-inch bolt secures the rear lower control arm to the frame. This bolt has a 13/16- inch head. Insert it through the control arm steel shaft from the top. Attach a nut to the bottom of the bolt using a 7/8-inch socket on the nut and a 13/16- inch wrench on the bolt head and torque it to 100 ft-lbs.

Step-4: Install Control Arms

The upper and lower control arms should look like this once they have been installed. Do not tighten the upper and lower control arm bushing bolts yet. These arms need to be moved up and down during the spring and steering knuckle installation. They will be tightened and torqued when the completed car is sitting on its wheels and ready to drive around the block.

Spring

The 1968–1982 Corvettes use a steel coil spring in the front suspension. The weight and type of engine (small- or big-block) largely determines the spring rate of the particular car. The standard front coil spring is rated at 474 pounds. Cars equipped with a big-block require a firmer spring as does the F-41 sports suspension option. Be sure to select the correct front spring for your particular model and/or application.

Optional equipment, such as air conditioning, also impacts the spring rates that are recommended by the factory. Original-equipment spring rates usually give the best ride if your only intent is cruising with your restored Corvette. However, if you are going to aggressively drive your Corvette or use it for autocross competition, install a front spring with a higher spring rate.

The spring should look like this when installed in its correct position. Notice how the end of the coil spring rests in the lower control arm. If it is not properly seated use a pipe wrench to rotate the spring into the correct position.

Place a floor jack under the lower control arm so it rests on the jack. Push the spring up into the upper control arm spring well in the frame. Use a long pry bar or long screwdriver to push the lower part of the spring into the lower spring well. You can also kick it with your shoe to push it into its deep well. Rotate the spring until the end rests against the lower control arm spring well dimple. Make sure the spring is properly seated in the control arm so it does not slip. Once the spring is securely in both wells, slowly raise the jack to prevent the spring from popping out of the upper and lower spring wells.

Remember to buy springs in pairs because each manufacturer has slightly different production methods that affect spring rate and height. The lower control arm has a deep well that supports the bottom of the front suspension coil spring. The control arm has a dimple stamped into it and the end of the bottom coil must rest next to this dimple.

The installation procedure is the same for all front coil springs. It is not diffi cult but care must be taken to avoid injury to yourself or others.

Steering Knuckle Spindle

The steering knuckle spindle plays a crucial role in front suspension dynamics. It connects the upper and lower control arms via two ball joints. In addition it houses the front wheel bearings, brake rotors, calipers, and brake lines. The front steering system connects to the spindle on each side of the car to provide steering to the front wheels. This part takes a lot of stress and should be closely inspected to ensure that it is in excellent condition before installation.

Steering Knuckle Installation

Step-1: Install Knuckle Wheel Bearing Assembly

Install the spindle dust shield gasket onto the spindle. Push the gasket to the back of the spindle. Grease and pack the inner and outer bearings with wheel bearing grease. Push the inner seal onto the spindle assembly. Install the outer bearing and follow that with a fl at washer. The fl at washer has a notch that matches the one on the spindle to prevent it from turning. Install the nut and tighten it until the hub barely turns. Loosen it one quarter turn and install the cotter key. Recheck the adjustment after putting 100 miles on the car.

Step-2: Attach Spindle to Front Suspension

Insert the lower ball joint stud into the opening on the steering knuckle. Use a 1/2-inch-drive torque wrench with a 7/8-inch nut and torque it to 75 ft-lbs. Be sure the cotter key hole lines up. If it doesn't, adjust the nut until the opening is located. Install a cotter key through the opening and bend back the two wires to prevent the nut from coming loose. Clip off the excess ends with a pair of cutting pliers.

Step-3: Install Steering Knuckle

If you have someone stand on the upper control arm during this procedure, installing the steering knuckle is easier because the suspension is being compressed from above and below. Slowly raise the jack, while the upper knuckle ball joint opening is placed into the top control arm ball joint stud. Observe the coil spring and make sure it stays securely in its upper and lower wells. It must not slip because it can cause injury if it does. Once the knuckle has been pushed into the ball joint stud, secure it with a 3/4-inch nut and torque to 45 ft-lbs. Once this nut is secure, your helper can exit his or her perch on the frame. If the cotter key hole doesn't line up, adjust the nut until the hole is located. Install a cotter key through the hole and bend the two wires back to prevent the nut from coming loose (as you did on the lower ball joint). Clip off any excess wire with a pair of cutting pliers. Slowly lower the jack to see if the upper and lower control arms securely hold the coil spring in place. Once the spring has been secured, remove the jack. Use two 11/16–16 x 7/8-inch bolts to attach the front caliper bracket and dust shield to the knuckle. Torque these bolts to 70 ft-lbs with a 5/8-inch socket.

Step-4: Inspect Steering Knuckle

This is how the steering knuckle looks when it is properly secured to the upper and lower control arms.

Step-5: Install Dust Shield

Install the wheel bearing dust cap along with the caliper bracket and dust shield.

Bump Stop

The bump stop is a triangle of rubber mounted to a metal bracket. This bracket is attached to the lower control arm on each side of the front suspension. The bump stop protects a severe bump or hole in the road. These are fairly inexpensive and it is a good idea to install fresh bump stops when putting the front suspension together.

Once the spring has been correctly installed, install the lower control arm bump stop. Use two 1/2-inch bolts and two 1/2-inch nuts to secure the rubber bump stop to the lower control arm. Torque these bolts to 35 ft-lbs. These bump stops play a very important role in protecting the suspension in case you hit an unexpected bump too fast and the suspension bottoms out. These rubber bushing are strong enough to absorb the impact under most conditions.

Shock Absorbers

The shock absorber is inserted from the bottom of the lower control arm and secured with two bolts in the front suspension. It uses rubber bushings and washers to minimize noise in the car. They are attached to the frame between the upper control arms with one bolt.

As a general rule, shock absorbers do not have a long life. Depending on your driving style and the type of shock installed, expect to get 15,000 to 30,000 miles on a new set. Original-spec shocks have a service life that's at the lower range of this estimate, while premium aftermarket shocks last at the upper range.

Aftermarket suppliers offer a wide range of C3 Corvette shock absorbers. Some even include multistep adjustments to dial in the ride you want. For autocross or track day events, set the shocks on the firmest setting as this provides the best handling. Just be sure to dial them down after you are finished playing or your fillings might fall out.

Shocks lose their effectiveness slowly, so keep this mileage in mind when you are budgeting for maintenance.

Steering Box

The steering box contains worm gears that turn the Pitman arm, which is attached to the bottom of the unit. At the top of the box, an adjuster is used to tighten worn gears.

Install the lower washer and rubber bushing onto the shock shaft. Feed the shock through the bottom of the lower control arm and insert the top of the shaft into the opening on the frame. Push a rubber bushing onto the upper shock strut until it seats against the frame. Add a washer and use a socket and ratchet to tighten the 9/16-inch nut onto the shaft. Secure the lower shock with two 1/2-inch bolts and torque to 35 ft-lbs. You may have to use a small wrench on the upper shaft to prevent it from turning as you tighten the 9/16- inch nut. Tighten the nut when the rubber has been slightly compressed on the shock shaft. Do not overtighten. Repeat this process on the other side.

Three bolts fasten the steering box to the left side of the frame. Use a torque wrench to secure the box with 9/16-inch bolts and torque to 30 ft-lbs.

This cutaway of a C3 steering box shows the inner workings of this critical part. The large block moves up and down the shaft as the steering wheel is turned. The block is attached to the Pitman arm gear that turns the steering system when it moves back and forth.

Third-generation Corvettes use a series of rods attached to the steering box and the suspension steering knuckles to turn the wheels. Power-assisted versions feature a hydraulic pump that is driven off the engine, and it pushes fluid into a ram that greatly reduces the steering effort. The ram (shown) is attached to the relay rod. Notice where the relay rod is attached to the passenger-side idler arm sleeve. The tie rod screws into the sleeve and connects to the steering knuckle. The relay rod also connects to the idler arm (far right). The idler arm provides support to the steering system and is connected to the passenger side of the frame. The ram mounts to the relay rod (right) and connects to a bracket on the frame on the driver's side. Two hydraulic hoses connect to the ram and provide fluid pressure to make the unit operate.

The relay rod connects to the steering box Pitman arm (lower left). This is a manual steering application, which is why power steering components are not seen in this photo.

Steering is a vital function for the car's safe operation and a worn or failing steering box needs to be replaced. If your box has high mileage and exhibits free play, it should be exchanged for a refurbished unit with new gears and original equipment adjustments. Refurbished units are fairly inexpensive and return a Corvette's steering to its original responsive feel.

Steering Linkage

The 1968–1982 Corvette steering linkage was first used in the 1963 Stingray. The recirculating ball unit is attached to an arm connected to a relay rod. The relay rod connects to tie rods on both ends, and those are attached to the steering knuckles. This is how toe-out and toe-in are adjusted on the front suspension. It is a little complex but works very well when adjusted correctly.

A belt drives the power steering pump. The pump is connected to the power valve and the power steering cylinder. The fluid pressure reduces the effort it takes to turn the steering wheel. The seals tend to leak if they sit or have high mileage. Low fluid greatly increases the pressure it takes to turn the wheel and quickly burns out the power steering pump if oil is not added. This should be part of your routine maintenance check under the car.

The completed steering system looks like this unit underneath a 1972 Corvette. Notice that it is equipped with power steering. All of the power steering hydraulic hoses are installed.

Two U-shaped brackets that fit over two rubber bushings secure the antiroll bar to the frame. Four 1/2-inch or 9/16-inch bolts, depending on the year the car was built, fasten the brackets to the frame. The bolts that you bagged and tagged when you removed this unit should be the correct size. Torque them to 30 ft-lbs. Connect the anti-roll bar to the lower control arm via an end link on each side of the front suspension. Two 9/16-inch nuts secure the links. Hand tighten until the bushings are slightly compressed. You might have to wait until the weight of the engine compresses the springs enough to install the links, or have some friends sit on the frame to help make the connection.

The trailing arm in this 1969 convertible is being removed so it can be overhauled by Van Steel.

Anti-Roll Bar

Standard non-performance Corvettes are fitted with a front antiroll bar that is designed to provide a smooth ride. They are usually ¾ to 1 inch in circumference. Cars that are equipped with FTL and big blocks are fitted with larger front bars and rear anti-roll bars to help balance the handling.

The aftermarket offers anti-roll bars for both front and rear suspension that are larger and stiffer than the stock anti-roll bars. The larger the bars, the more taut the ride. However, cornering speed is greatly increased with bigger units.

Rear Suspension

The C3 rear suspension was an engineering breakthrough when introduced in 1963 on the C2. The design was so successful that it was carried over for the entire C3 production run with only minor changes. The most important change occurred in 1981 when the factory installed a composite rear leaf  spring. These springs were installed on Corvettes built at the new Bowling Green assembly plant. They provided a better ride and reduced the unsprung weight of the rear suspension.

With the C3 rear suspension design, the differential is mounted to the center of the frame and two halfshafts connect to the rear wheels. Two trailing arms are bolted to the frame on each side and held up with a transverse steel spring (1968-1980). The trailing arms house the parking brake, brake calipers, and rotors. The rear shock absorbers are attached to the trailing arms at the bottom and to the frame at the top.

This system greatly improved handling and ride and that is why it was installed on all C3 Corvettes.

Trailing Arms

C3 rear trailing arms are made from boxed steel and welded for strength. One bolt holds these arms in place. Add or remove shims to adjust the toe-in or toe-out of the rear suspension.

When you disassembled the frame, you paid particular attention to how many shims were installed before removing them. Reinstall the suspension with the same number of shims to return it to its previous setting. Even if you use the same shims in the same location, always take your completed Corvette to an alignment shop. A professional can put the correct suspension settings back into your car.

The arms are robust but the bearings are prone to failure. Refurbished trailing arms include new bearings as part of the price. If you are refurbishing these trailing arms yourself it is wise to include new bearings. To reassemble the trailing arms, simply reverse the disassembly procedure discussed in Chapter 6.

Trailing Arm Installation

Step-1: Remove Trailing Arm Assembly

Remove the parking brake hardware (reverse the procedure that starts in Step 3). Use a 9/16-inch wrench to remove the four nuts that are located underneath the parking brake hardware. Insert a pickle fork between the trailing arm and the bearing support legs. Use a hammer to strike the pickle fork to knock the trailing arm away from the bearing support. (Van Steel uses a special fixture to press the spindle out of the bearing support.) Remove the races and seals and clean the trailing arm in a parts washer to remove the grease and grit. Shot peen the rear trailing arm until all the paint and grime have been removed. Then insert the arms into a special jig to verify that they are straight. If they pass the inspection, send them to the powdercoating shop so their surfaces can be powdercoated to prevent deterioration.

Step-2: Reassemble Trailing Arm

Reassemble the powdercoated arms. Add the right rear bearing support to the unit. (The front trailing arm bushings have already been installed here.)

Step-3: Rebuild Parking Brake Assembly

Install and adjust the parking brake assembly prior to mounting the rear brake rotor. It is easier to install the lower adjuster and the spring first on the workbench. Lift them and spread the shoes to mount them on the upper pivot bolt. Install the side pins with a spring cup and then install the upper spring. Final adjustment is complete when the brakes and new parking brake cables have been installed in the car. Verify that each bolt has been properly installed and torqued to specifications by marking them with White-Out.

Step-4: Install Brake Rotors

Install the rear brake rotor over the hub and check it for runout to verify that the rotor and bearings are within factory tolerances. Tolerances of .005 or less are the runout target. Any out-of-spec measurements cause an annoying vibration that can be felt throughout the vehicle. It is critical to catch any imperfections on the workbench and not on the car. If your rotors are new and out of spec, return them to the vendor for a refund. You need to have properly functioning brakes with no thumping or pulsating from out-of-spec rotors.

Step-5: Verify Trueness of Trailing Arm

Place a dial indicator over the rotor to to verify rotor trueness. Secure and tighten all lug nuts. The rotor is now ready to be installed. Notice that these rotors have been matched to the spindle for trueness with White- Out. It is not necessary to return the same unit to your car. It is much quicker to exchange your old trailing arm for a refurbished one.

Step-6: Install Trailing Arms

Install the trailing arm into the slot in the frame. Insert the trailing arm bolt through the trailing arm. Lift the trailing arm from the rear and place a 1 x 1-inch piece of wood into the same place that the shims go. This puts the trailing arm in the correct ride height position and makes putting the half-shafts and strut rods into the car much easier. The shims will be installed later; do not put them in now. Also do not tighten the trailing arm. This will be one of the last bolts to tighten.

Differential

The differentials are basically all the same inside, but you find some minor changes during an overhaul. The outer case material changed to aluminum in 1980 to reduce the weight of the rear suspension. Subtle changes were made to the rear frame to accommodate this new differential. This new design can be found in all 1980–1982 Corvettes.

Many Corvette suppliers offer bearing and clutch pack kits that make an overhaul procedure much easier. The kits include all of the necessary parts.

When taking a differential apart, be sure to mark the left- and right-side pieces. It also helps to place a piece of colored tape on each side of the bench to keep the left- and right-side parts separated. Laying them out on your workbench in the proper order will help you identify the correct placement of these parts during reassembly.

Teardown

When draining the oil from the differential, check for a burning odor, which indicates overheating of the gears and case. Also check the oil for any metal fragments, which tell you a gear tooth might be chipped or broken.

This cutaway of a C3 differential reveals the components to inspect when the rear case cover is removed. Teeth marks on the Posi- Traction case indicate that the bearings are worn and the pinion gear is hitting the case.

Worn or Broken Gears

After the oil has been drained, remove the back cover on the differential. Slowly rotate the gears to check for any obvious signs of one gear rubbing on another.

Loose Gears

Move the gears back and forth to check for looseness and play from side to side. If you find this problem replacing the bearings and shims should correct the issue.

If your original differential is not making noise and does not show any evidence of abnormal wear, reinstall the old shims. Your objective here is to install fresh bearings, seals, clutch packs, and races to replace any worn parts in the differential.

A J tool from General Motors is required to accomplish this task. Use an adjustable micrometer to verify the thickness of any shim before installing it. This photo shows a typical pinion bearing with a crush sleeve between the inner and outer bearing. Note that a shim (.028 in this case) is below the inner bearing and the driveshaft yoke has been attached to the outer part of the pinion bearing.

Install Pinion Seal and Driveshaft Yoke

Step-1: Lubricate Pinion Seal

Apply silicone lubricant before installing the seal gear into the housing. Use engine assembly lube to perform this task. This is a good preventive maintenance procedure to makes sure the parts are not dry.

Step-2: Install Pinion Seal

It is important to make sure that this seal is correctly seated into the top of the differential housing. Use a large piece of pipe or something that is the same diameter as the seal. Make sure it sits evenly on the lip of the housing then use a hammer to gently tap the seal into place. Be careful; the seal is easily damaged.

Step-3: Establish Seal Clearance

The thickest shim in your clutch pack (.045 inch) is used to ensure that the bottom part of the seal does not bottom out, which causes leakage. Carefully continue to tap the seal in place while moving the shim around to ensure that the gap is the same all around.

Step-4: Install Driveshaft Yoke

Install the washer. Use a liberal application of silicone on the washer (shown) to make sure there are no differential oil leaks. Then install the nut and tighten until you get the proper drag on the nut (18 to 22 inch-pounds) on new gears. On used gears it is 15 to 17 inch-pounds.

Step-5: Seat Driveshaft on Pinion Shaft

Place a solid bar such as a damaged pin (shown) on the driveshaft yoke. (You can also use a large punch or another piece of solid metal.) Tap it several times with a mallet or hammer to make sure it is seated properly on the pinion shaft.

Step-6: Measure Pinion Resistance

Confirm the drag or load on the pinion by using an inch pound torque wrench. About 18-inch pounds is common for this step. Do not overtighten this nut because the bearing could seize.

Posi-Traction Clutch Pack

The Posi-Traction unit has small clutches that are stacked on each side of the springs; they are held in place with these springs. They perform an important function. If one wheel loses traction the clutches engage and lock both wheels to provide added traction. Worn Posi-Traction clutches often chatter at low speeds when making a sharp turn. New clutches usually cure this problem.

This illustration shows some but not all of the major parts in a Posi-Traction unit.
1. Posi case
2. Pinion shaft
3. Pinion lock screw and washer
4. Pinion gears
5. Pinion thrust washers
6. Side bearings
7. Clutch pack guide
8. Clutch discs
9. Clutch plates
10. Yoke

Assemble Differential

Step-1: Stack Clutch Pack

Lubricate all of the clutch discs thoroughly on both sides with GM Posi-Traction additive. Don't forget to do this; it's important. First start stacking a side gear with a clutch disc that has two tabs or ears on it. Five of these discs have tabs. This tab piece goes onto the side gear first, and then every other disc added to the stack does not have tabs. Four discs without tabs are on each side. The final piece is a shim that determines the side yoke measurement. The best place to start is with the shim that came out when it was disassembled. The endplay on the side yoke should be .005 to .010 inch.

Step-2: Install Clutch Pack in Housing

After the clutches and side gears are installed, insert a thrust washer on each side of the unit. Rotate the Posi clutch pack unit (shown on a jig in step 4) until you have enough room to insert the washer.

Step-3: Measure Endplay of Side Yokes

You are looking for a clearance measurement of .005 to .010 inch. If it is not within this range, the assembly needs to be removed and a different-size shim installed. Repeat this process until you get the correct measurement.

Step-4: Install Spring Plates

Assemble the spring plate and put it into a vise. Secure it with a hose clamp around the center and then tighten the clamp enough to compress the spring plate so you can slip it through the window (shown). Once the spring is in the proper position, loosen and remove the hose clamp. The springs push against the clutches with more force as the car's speed increases. They lock the clutches and provide power to both wheels. Recheck the side yoke endplay. If there is excessive play, add shims to eliminate it.

Step-5: Break In Limited-Slip Differential

Van Steel constructed this tool to spin the Posi-Traction unit on a jig that is mounted to a post. They spin it fifty times to the left and 50 times to the right. Then it's removed from the jig and turned around to repeat this process in the opposite direction. This helps break in the limited-slip differential before it is put into service. The clutch plate stack should set in and therefore be ready for service once the differential is installed in the car.

Step-6: Install Ring Gear

Install the ring gear onto the Posi unit with new Grade 8 bolts and lock washers. Use a locking adhesive on the threads and torque each one to 60 ft-lbs. Cross tighten them as you do to secure a tire using the star method.

Step-7: Install Side Bearings

Use a mallet to carefully tap the side bearings into the case. Make sure that they are completely seated. Check theside plate end play again.

Step-8: Install Differential into Housing

Place the limited slip unit in the differential housing. Cautiously tap the side shims into the case to avoid damaging the cast-iron shims. (If you are using steel shims, this is not a problem.) If you use the original ring-and-pinion gear that was removed the fit does not require much adjustment. Torque the side caps to 60 ft-lbs.

Backlash occurs when you take your foot off the throttle; you hear a clunking noise coming from the rear of the car. Adjusting the backlash is the best way to eliminate gear noise. After the shims have been installed, attach a dial indicator to the differential housing to check the gear backlash. Put the dial indicator on zero; rock the ring gear back and forth to determine how much play it has while the pinion gear remains stationary. The measurement should be .006 to .008 inch. Add or remove shims that were installed in step 8 on page 105, depending on how far the measurement is from the desired specification. Yellow or white dye (or marking compound) is usually found in a differential kit. Apply some dye according to the kit instructions. To check the gear pattern, hold the yoke with one hand and turn the ring gear back and forth with the other hand and a 9/16-inch wench on the ring gear bolt. This marks the gears with the dye and shows your gear pattern.

Gear Mesh Pattern

If using a differential rebuilding kit, it includes a dye to help determine the gear mesh pattern. You use shims to make it match the desired pattern.

Frame Member

The completed differential now needs to be attached to the frame crossmember. It is best to sit the differential onto a jack and then install the frame member.

The ideal contact pattern (centered on the teeth) is the drawing in the middle. If your backlash is too large or too small you can shift the shims from one side to the other. If you take two shims out of one side, for example, you must place the same number onto the other side. (Photo Courtesy Van Steel)

The easiest way to prepare the differential for installation is to place it onto a floor jack. Attach the frame crosspiece to the differential with two 7/16-18 x 11⁄8-inch bolts and 7/16-inch lock washers.

This differential has been assembled and is ready for installation.

Raise the differential and cross frame with the floor jack until you can secure it to the frame with two 5/8-inch bolts. Torque the bolts to 70 ft-lbs.

Half-Shafts

Half-shafts connect the differential to the rear wheels. They are fitted with universal joints so they move through the arc of the suspension's travel as it encounters changes in the road surface. Big-block cars use a different attaching method than small-blocks. Make sure you have the correct bolts.

Rear Suspension Strut Rods and Shock Absorbers

You can adjust the strut rods to change the rear suspension camber setting on your Corvette. The rods mount under the differential and connect to the trailing arms on the same bracket as the lower shock mount. If you marked these parts during disassembly, re-torque the bolts to the same location. This is a good procedure to complete before taking the car to the alignment shop.

Small-blocks from 1968 to 1979 use two U-bolts on each side to attach the shaft to the differential, which are secured with 9/16-inch nuts. Tighten the nuts evenly on both sides and make sure the lock washers are crushed. Once they are snug, go one-quarter turn more with a wrench. Be careful to not over tighten them, as it damages the roller bearings.

Big-block half shafts from 1968 to 1974 use 9/16 x 14 x 331⁄64-inch bolts and heavy-duty caps. Once they are snug, go one quarter of a turn more with your wrench. Be careful to not over tighten them, as it will damage the roller bearings. The 1980–1982 automatics use 12-mm x 1.75 x 10.9 x 35-mm bolts and 1980–1981 4-speeds use 12-mm x 1.75 x 10.9 x 80-mm bolts. Tighten the nuts evenly on both sides. Once they are snug go one quarter of a turn more. Be careful not to overtighten, as it will damage the roller bearings.

Four 9/16-inch bolts fasten the half-shaft to the trailing arm bearing. Install a French lock that serves as a washer. These bolts should be torqued to 30 ft-lbs and the tabs on the French locks need to be bent (shown). This prevents them from loosening and backing out.

The strut rods attach to the differential bracket with an adjustable camber bolt with two reducing washers inside the bushing on the differential side only. The other side connects to the bearing support leg and the shock mount is pushed through the legs and the strut rod. This configuration is why the small piece of wood was placed in the trailing arm to keep the ride height closer to factory specs. It is much easier to install the strut rod with the trailing arm in this position. Four bolts with 9/16-inch heads fasten both strut rods. Torque them to 35 ft-lbs. Notice here that the shock absorbers have been mounted and the halfshafts are bolted to the trailing arms and differential. The rear transverse leaf spring and spring bolts have not been installed. Remove the wood when this is complete.

This job is easier if someone is helping. Rest the spring on a floor jack and raise it to the differential to attach it with the steel plate and four 13/16- inch bolts. Torque these bolts to 100 ft-lbs. Make sure the guide pin on the spring aligns with the guide hole in the differential.

With the center of the spring secure, install the spring end links. To start, place a pair of locking pliers on one end of the leaf spring. Get some friends to sit on the frame as you perform the next part. Drop the end link into the opening at the rear of the trailing arm. Place a floor jack under the spring and slowly lift the spring until you are able to attach a nut to the bottom of the end link bolt. Once the bolt is attached with the nut and washer, slowly lower the jack. Your friends can now exit the frame. Use a 13/16-inch socket on the top and a 7/8-inch wrench on the bottom to tighten the bolt. Insert a cotter key in the provided hole. Repeat this step on the opposite side.

The frame has now been completed and rolled outside for a final inspection. We Mounted tires to make this job easier. The upper shock bolts (5/8- and 11/16-inch nuts) were torqued 60 ft-lbs. The 3/4-inch lower nut was torqued to 40 ft-lbs. The 3/4-inch inner camber bolt was torqued to 70 ft-lbs. The 15/16-inch shock mount nut was torqued to 75 ft-lbs. Also install the gas tank at this time.

Rear Spring

Two people may be required to reinstall the rear steel spring. Four bolts in the middle secure it. Each outer end of the spring is connected to the rear of the trailing arm with a link. This spring is under a lot of tension and might require the use of sandbags to be placed on the frame to help attach these end links.

Odds and Ends

Congratulations! The major mechanical components have now been correctly installed into your refurbished frame. It also has the front and rear suspension and the differential. This is the perfect time to install the gas tank between the back frame rails.

Written by Walt Thurn and Posted with Permission of CarTechBooks

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Source: https://www.chevydiy.com/c3-corvette-restoration-guide-suspension-differential-reassembly/

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