68 rear end Q

[David M.]

Under my April built 68 327 3spd and I noticed the shims between the trailing arms were loose. So much so I was able to pull them out. Shouldnt they be in there tight? I dont see the holes there for the long cotter pin that holds the shims as the later C3s have. Not on the body or the arms? Do I need to drill these holes? When I take this to get it aligned is there anything I should ask for specifically? Thanks. Dave

[Michael M.]

Re: 68 rear end Q

The trailing arm shims should be tight. Very tight so they don't fall out as that will cause alignment problems and other issues (the rear end will be very loose). I believe in '68 the proper shims had holes for the bolts to go through and not slots. It is very common to see the slotted shims being used becasue this aids the alignment person. With the holes versus the slots the trailing arm bolt must be removed to alter the shim packs. Many times if the car has been changed to slotted shims, people will drill a hole through the frame and insert a cotter pin to prevent the loss of the shims if the bolt loosens up.

[Terry M.]

Re: 68 rear end Q

In production the slotted shims didn't begin until the last week of 1970 production. The hole in the frame for the long cotter pin began during 1969 production -- I would have to look at the AIM to guess at when during that long production year. So from 1969 model year to the end of 1970 production there was a hole in the frame and no cotter pin was used.
The forward control arm retaining bolt should be tight enough to keep even the slotted shims in place. Additionally the slotted shims can usually be rotated into the frame pocket and that pocket will catch the end of the shims to keep them from sliding out.
If you wish to be absolutely NCRS judging correct, have the shop align the rear with the slotted shims, then replace the slotted shim packs with the correct ones with the hole, making the packs the same thickness. One can usually do the R & R of the shim packs ones self.

[Jim T.]

Re: 68 rear end Q

Terry my original owner 70 still has the original shims, it was built in July and the my original shims have the hole, they are not slotted. My last alignment the technition tried to remove a shim thinking they would be slotted. I was standing beside him and told him the bolt has to come out to change them. After an alignment I checked the shims when I got home and could move them, I have had to tighten the control arm retaining bolt because the technition did not tighten it enough.

[Terry M.]

Re: 68 rear end Q

Jim -- the last week of 1970 production would have trim tag dates of G27 to G31 (July 27 to 31). Serial numbers greater than about 16700. Off the top of my head I don't recall the serial numbers I examined to determine this. It was quite a few years ago.

[David M.]

Re: 68 rear end Q

Thanks all who responded. This one-year-wonder is a learning experience:) That's why I have not driven it since discovering this problem while doing a 4 wheel brake job, dont want to stress the car/chassis with a loose rear. I have worked on a few C3s but later vintages and they all had the cotters and slotted shims. Its been a while since I've had one aligned. Any new technology(s)I need to ask for (or be made aware of) or is it still just considered a complete 4 wheel thrust alignment? Thanks, Dave

[Terry M.]

Re: 68 rear end Q

A 4-wheel alignment will do, if you can find someone who is willing and knowledgeable about the Corvette IRS. There are new fancy whizz-bang laser machines, but they are no more accurate than the old light and mirror machines -- they all still depend on the skill of the operator. In fact the newer computer-driven laser machines may not have the 1963-1982 Corvette alignment specifications in their memory -- too old. You might want to bring copies with you of something that has the specifications -- the AIM or FSM pages with those numbers. A skilled operator can input your specifications in place of missing or inaccurate numbers in the computer memory.

If you don't have an alignment shop (a real suspension/frame shop, usually not the local tire emporium) that has come to you recommended by someone else with a 1963-1982 Corvette, you might want to stop by or call and ask the technician who will be doing the work (not someone behind a counter in the office) about your situation. If he gets the deer in the headlights look, go elsewhere.

[David M.]

thanks all and terry *NM*