Refurbishing Suspensions

Q: Refurbishing Suspensions

Since there seemed to be others interested in refurbishing their suspensions, I am posting my experience in working on mine and a question about a noise problem.

Over the past few days I worked on both the front and rear suspensions of my 1968 Firebird 400. I replaced the 30-year-old springs and 16-year-old bushings and, in the case of the front-end, the ball-joints, along with a few sundry items. Below is a description of what I did, the results, and a plea for help with one problem.

Front: I used standard MOOG bushings and ball-joints, just like last time, and Classic Industries’ coil-springs and bumpers. A local machine-shop did the actual control-arm work. This was long-overdue maintenance (the upper bushings were missing large chunks of rubber). Getting the lower control-arms to line up with the frame (re-assembly) was even less fun than I remembered it being the last time I did this. I would LOVE to have the original GM tool for this step.

Rear: I used Classic Industries’ leaf-springs and mounting kit. The old springs had 5 leaves. The new springs had 5 leaves and a thick mounting plate on the bottom side. The combined thickness was too much for the mounting hardware, so I removed the plate (which made the new spring look more like the old spring) and mounted the remaining assembly.

The mounting kit came with two U-bolts per leaf, but the original assembly had one U-bolt and two smaller bolts per side. The new U-bolts were longer than the originals and extended closer to the ground, so I used all of the original bolts.

The mounting kit also came with new shackles and hardware, which I used, with the exception of the shackle nuts and the front eye bracket-to-frame press-nuts. The old shackle nuts were the more-secure cinch type (like a castle-nut, but the slots aren’t big enough to accomodate cotter pins); the new ones were plain. The old bracket-to-frame nuts were more substantial than the new ones.

The hardest part was the requirement that all the bolts be torqued after the car is on the ground. I definitely could have used a lift or a service pit.

Results: The ride height increased by roughly an inch, both front and back. The suspension once again has life to it, and the car no longer bottoms out during normal driving (haven’t tried getting airborne yet). The steering is tight again. Thanks for all of the advice/information I received here. The project was a definite improvement.

Problem: However, between 30 and 40 MPH, VERY low-frequency road noise is amazingly loud inside the car. Until now I’d never had this problem. Does anyone know what this is? Are the new mounting pads to blame, or perhaps removing the spring mounting plates? Will the sound lessen over time? It’s really loud, and very low frequency. I’d appreciate any input.

A: Did you use/replace the rubber isolators on the new rear springs? Mounting them solidly is OK for road racing or drag racing but not good for street cruising. Also what kind of spring and a-arm bushings were used /replaced? forget the urethane for the same reasons. Stick with the GM stuff for the nicest package.

A: The problem turned out to be the shackles rubbing on the body. The bolt holes on the new shackles in the installation kit were about a quarter inch farther apart center-to-center than the old ones. The added length made the bottom edge contact the body panel below the rear bumper.

Thanks for the suggestion. All bushings are plain rubber. The new springs came with new stock rubber bushings. After this experience, I don’t even want to think about solid mounts.

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