Torque Arm Shim Question......

[Patrick T.]

When I rebuilt the rear suspension in the spring, I purchased a set of new stainless alignment shims, with one end slotted and the other end, a hole. The original shims I took out, had holes on both ends. When I inserted the correct shims onto the long forward bolt, I tucked the shims down into the frame, to keep them from sliding out. There was no side play and the nut was torqued to 55 lbs.

Now I just noticed a couple shims on one side only have moved upward, out of the frame and have started to squeeze out. I tried to move them by hand, but they are still relatively tight.

When I bought the kit, it came with two 4" long cotter pins, presumably to keep the shims in place, but I didn't use them, although I still have them. I checked the '67 shop manual, and there is no mention of any cotter pins, because both ends of the shim have holes only, so the bolt would keep them from sliding out.

I'm assuming the cotter pins have to go through the holes which protrude out the frame, but it looks evident that the holes are way too big to hold the cotter pins. Any advice on how to install these pins and keep the shims in place? Thanks, Patrick #33001

[Joe L.]

Re: Torque Arm Shim Question......

Patrick-----

All 1967 Corvettes originally used the rear toe adjustment shims which had holes on either end. Consequently, these cars did not need the cotter pin to provide a "fail-safe" means of shim retention.

In late 1969, or so, the shims which were slotted on one end began to be used in order to facilitate rear toe adjustment procedures and avoid the need for removal of the trailing arm pivot bolt. Consequently, beginning in late 1969 holes were added to the frame for installation of the cotter pins. My original owner late-build 69 has the holes. Originally, it had a mix of slotted and non-slotted shims. I presume that about the time that my car was built (mid-September, 1969) they were phasing out the old shims and phasing in the new. So, I got a mixture. Also, although my car has the holes for the cotter pins, no cotter pins were originally installed.

In any event, I always recommend using the slotted shims as it GREATLY speeds up rear toe alignment procedures. Since many shops charge for Corvette rear alignment only by the HOUR, this can save one considerable money. Plus, on the car, the slotted shims are virtually undetectable.

Of course, if you add the cotter pin holes, that will be VERY detectable. I can tell you this for sure: beginning with my car's second rear toe alignment, I had the Chevrolet dealership replace ALL of the shims with the slotted type. I never used the cotter pins even though the holes are present in my frame. And, I've never had any problems whatsoever with displaced or thrown shims.

[Duke W.]

Re: Torque Arm Shim Question......

The space on either side of the bushing must be firmly packed with shims, to the point where they will stay in by themselves due to friction. I assume you had some 1/32" shims in case you needed them.

My suspicion is that you didn't get the gap full, so there is insufficient'preload on the shims and bushing. If the shims are moving, the metal inner bushing sleeve is probably rotating against the bolt.

All rotational movement of the trailing are should be deflection of the rubber in the bushing. There should be no metal to metal movement. Also, the bushing through bolt should be torqued with the rear suspension at normal ride height. Otherwise, the bushing will be preloaded in torsion, which will shorten bushing life.

Duke

[Patrick T.]

Re: Torque Arm Shim Question......

Duke, thanks for the tip, I did have a few 1/32" shims included in the setup. The car was on jackstands when I loaded the shims up and it was packed full, with no gap. But I will reinstall and torque at normal ride height. Patrick

[Duke W.]

Re: Torque Arm Shim Question......

With the suspension drooping the clearance between the bolt and the bushing inner sleeve will cock the bushing enough that you probably can not get a good tight shim pack. Figure out a way to get the suspension to normal ride height. On my drum brake car I can rest the drums on wood blocks, which will get it close to normal suspension ride height and then put some weight in the back.

Not sure if you can do this with disks, because of the dust shield. The best way would probably be to disconnect the spring at the end links. Thats an easy job! Then block up the rear supension until you have the correct "Z" height as listed in the shop manual. Then you can properly measure the toe and pack enough shims to get it tight, and properly torquing the bolt will lock everthing in place for a long time.

Duke