'68 Corvette Rear Suspension Upgrade
Performance Upgrades For A Sharks Rear Suspension
From the February, 2009 issue of Corvette Fever
By T.J. Cook
Photography by T.J. Cook
Our upgraded rear suspension...
Our upgraded rear suspension components from Mid America Designs: ACDelco performance gas shocks, adjustable urethane strut rods, performance rear spring, rear sway bar, trailing arms, and related components. Not pictured are the rear spindle assemblies.
Get the spare-tire assembly...
Get the spare-tire assembly out of the way: First, remove the lower tray and upper tub of the spare-tire-carrier assembly. This will allow you better access to the rear suspension and will provide ample room for the installation of the rear sway bar later in the process. Remove the shock: Place a hydraulic floor jack under the shock mount and raise it in order to relieve pressure from the shock and leaf spring. Remove the shock absorber from the bottom bolt on the shock mount stud. Remove the top nut and bolt from the frame. Remove the strut rod: Remove the cotter pin from the shock bolt stud and remove the nut. Go to the strut rod support bracket. Look at the notches on the strut rod bolts and the notch on the strut rod support bracket. Mark the two notches so that you can align them at the same spot upon reassembly. This wont give perfect alignment, but will give the alignment shop a good starting point. Loosen the strut rod nut and bolt, then remove them. Place a prybar on the top end of the strut rod and support bracket and pry downward to release the strut rod. Release the floor jack. Then use a spreader tool to release the strut rod from the shock mount.
Remove the leaf spring: Place...
Remove the leaf spring: Place the jack approximately 3-4 inches from the end of the leaf spring and jack up the spring. Do not go too high and lift the car off the stands. Loosen the nut and remove the rear spring bolt from the trailing arm and spring. Lower the jack slowly to drop the pressure off the spring. Once the other side is done, youll need to remove the four rear spring center plate bolts to completely remove the leaf spring.
This article assumes replacement of both the trailing arm and spindle assemblies. If you are not replacing the spindle assembly or the trailing arm, the following two steps of disassembly are not necessary. If you are replacing only the spindle assembly, removal of the trailing arm is not necessary.
Remove the spindle and trailing...
Remove the spindle and trailing arm assemblies: Remove the four halfshaft bolts from the spindle assembly. Loosen the brake line from the caliper and unbolt the caliper from the spindle assembly. Release the parking-brake cable assembly from the top of the spindle. Go to the forward lower area of the fenderwell and remove the cotter pin from the trailing arm nut. Remove the nut and remove the bolt using care to catch the spacers that are removed from both sides of the trailing arm. Set these aside for reinstallation in the exact same positions, as this is not a setting that will be corrected by the professional alignment, but rather a factory specification for proper alignment of the trailing arm. The trailing-arm assembly will then slide free of the frame channel. Due to the rotor and spindle assembly, this unit will be rather heavy.
Remove the spindle from the...
Remove the spindle from the trailing arm: Remove the brake rotor. (If the rotor has never been removed, youll need to drill out the factory rivets in order to take the rotor off.) The parking-brake assembly should not need to be loosened since youve already removed the parking-brake cable. Slide the rotor off. Remove the parking-brake shoes to gain access to the trailing-arm-to-bearing-housing nuts. Loosen the nuts and separate the spindle assembly (consisting of the caliper mounting bracket, trailing-arm-to-spindle support, rear wheel U-joint yoke flange, rear spindle, spindle hub, and bearings, seals, etc.) from the trailing arm. Be sure to mark the spindle assembly noting which side it came from. If you dont mark them and get them reversed, youll know it when you try to reinstall the shock and the bracket is backwards!
Install new body bumpers:...
Install new body bumpers: Between the frame and the trailing arm is a V-shaped rubber bumper that prevents the rear suspension from bumping the frame. If this item needs replacement (if its cracked or worn), this is a good time to simply remove the old, and replace with new. Its held by a single nut. Install the new trailing-arm assembly: Insert the end of the new trailing arm into the frame channel. Carefully replace the shims on both sides between the trailing arm and the channel while inserting the bolt. Once the bolt is in place, tighten the nut and set the cotter pin.
Reattach the new spindle assembly:...
Reattach the new spindle assembly: If youre installing new trailing arms, you may have to transfer the four mounting studs from your old arms to the new ones. Place the spindle assembly as described above (be sure its the right one for a given side) onto the trailing arm studs and tighten the nuts. From the old assembly, remove the shock mount and reinstall it on the new assembly, making sure its from the correct side. Reassemble the parking-brake shoes. Its easiest to complete the rear suspension upgrade without the rotor in place, since youll need to move the trailing arm around. Reattach the halfshaft back to the spindle assembly by replacing the four bolts we removed earlier.
Install the new leaf spring:...
Install the new leaf spring: Be sure to orient the new leaf spring so that it points downward on each end. Align the small center stud on the backside of the leaf spring with the factory indentation on the bottom of the rearend. As you turn red in the face holding the spring, place the center mounting plate on the bottom side of the leaf spring and start each of the four bolts into the rearend. Once the bolts are started, the weight of the spring will be on the center mounting plate. So that the spring lifts evenly, tighten the bolts in a cross-alternating fashion until the bolts are all fully tight. As you tighten, be sure that the line-up stud aligns correctly with the rearend.
Place a floor jack 3-4 inches...
Place a floor jack 3-4 inches from the end of the leaf spring and raise it until there is about 2 inches from the bottom of the trailing arm to the top of the spring. Insert the rear spring bolt through the trailing arm and through the spring using the correct bushing/spacer placement (beginning at the top of the bolt: washer, bushing, washer, trailing arm, opening, leaf spring, washer, bushing, washer, and nutin that order). Lower the jack.
Install the new adjustable...
Install the new adjustable strut rod: Adjust the length of the new strut rod to match the old one. The adjustability of these strut rods is designed to provide better alignment and more refined performance handling. Note that when alignment is professionally done with these, it is done according to factory specifications. If you change the adjustment yourself, you are, in effect, changing the alignment and could cause improper tire wear and poor handling. Next, connect one end to the shock mount and install the bolt through the shock mount and add the nut. Raise the strut and align it to attach to the strut rod support bracket. If necessary, use your floor jack and raise the trailing-arm assembly from the shock mount. Once you have it aligned with the hole, install the strut-rod bolts and put the nuts on. Then, line up the notches from the support bracket to the strut-rod bolt. Now tighten the strut-rod adjustment nuts.
Install the new shock absorber:...
Install the new shock absorber: Jack up the trailing-arm assembly from the shock mount, keeping the jack clear of the threaded area. Insert the bottom end of the shock into the shock-mount threaded area and nut it. Raise the top of the shock to the frame channel where the shock was previously unbolted and bolt it back on. Release the jack.
Installation of Sway Bar...
Installation of Sway Bar (optional step): Our project car did not previously have a sway bar (most sharks would not), but we chose to add one for enhanced performance. Attach the sway-bar mounting plate to the top end of the trailing arm by drilling two 1/4-inch holes through the top end. Space the holes according to the bracket. Then bolt and nut the mounting plate in place. Attach the urethane bushing approximately one inch from the 90-degree bend on both ends of the sway bar. Hold the sway bar in approximately the correct position and youll note that two factory-placed nutted holes are preexisting in the frame. Place the urethane bushing so that it falls between these two holes, cover the bushing and holes with the mounting bracket, and bolt in place. The ends of the sway bar must be above the sway-bar mounting plate. Jack the trailing arm/spring assembly up to the sway bar, and by pulling the sway bar down some, youll be able to get them within a few inches of one another. Then, bolt them together with the end-link bolts. Correct placement of washers, bushings, and spacers is important: bolt, washer, bushing, sway bar, bushing, washer, spacer, washer, bushing, mounting plate, bushing, washer, and nut. Tighten the nut approximately 1.5 inches onto the bolt and release the jack.
8 Reinstall the brake assembly:...
8 Reinstall the brake assembly: Reinstall the brake rotor, then reconnect the parking-brake cable. Adjust the parking brake. Reconnect the caliper to its mounting bracket on the spindle assembly. Reconnect the brake line to the caliper. Bleed the brakes and put the wheel back on. Dont forget to reinstall the spare-tire assembly. Job well done.
Our 68 was in dire need of many new rear suspension components. Much of what was existing was so rusty it was completely useless and needed replacement, so we decided to upgrade the components to include urethane bushings and a rear sway bar while we were at it. We completely redid the suspension, replacing the trailing arms and spindles.
Follow along as we lead you through this rear suspension project. Of course, well be explaining just one side of the car, and youll need to repeat the appropriate steps on the other side as well. When youre completely finished, have a professional alignment done.
As with any project where youll be beneath the car, carefully jack the car up and place it on jackstands. Be sure the car is in Neutral with the parking brake off. Remove the wheel and lets get started.
Mid America Designs
# 1 Mid America Pl.
P.O. Box 1368