Hi, this is my first post on this board, so please excuse my lack of knowledge. I've owned a 1966 convertible 327/350HP (L-79 ?) for about 11 years. I had a frame-off restoration done about 10 years ago, and the car has been only a weekend driver since then, with no major problems. A few years back I started getting a loud "clunk" and shimmy in the rear end when letting off the power in gear. It was mild at first and then the shimmy continued to increase. I finally discovered that it was caused by play in a rear trailing arm due to a loss of alignment shims. I took it to a Chevy dealer (only place in the rural town where I was at the time) and they realigned it with additional shims. Problem solved.

Recently the "clunk" has come back when letting off power, but the shimmy hasn't reappeared yet. There's minimal play in the trailing arm, but I suspect the shims or bushings are going in the rear end again. Also the left rear wheel sits about 3/4" closer to the fender than the left rear (and the fenders are straight in the back).

Does this sound like the same rear-end problem? Any suggestions on the best way to troubleshoot this without taking out the rear suspension? If it is the shims/bushings in the rear end, any suggestions on the best way to align it and keep it straight over time?

Thanks for any and all advice!

 

Hmmm, welp.......I would first check to see if'n the shims are again missing. If not I would change the rear end fluid. Make sure to add two bottles of limited slip additive. As for the tire to fender difference, methinks you're looking too closely. On the other hand, it could be a couple of things, (1) wheel bearing play is excessive, (2) rear end spindles wearing too much, or (3) u-joints are worn. A good vette shop could diagnose better. Oh, and howdy......... :cheers:

 

You might check the front differential mount bushing for wear, but it wouldn't cause one wheel to be further back than the other. If it wasn't originally like that about the only thing that could cause that would be the trailing arm bushing totally disintigrating or the rear kickup part of the frame parting company with the rest of the frame. I would jack up the rear and yank and pry around on things to see if you can find something loose. Welcome to the board. :steering:

 

:iagree: The bushing above the pinion yoke is the usual suspect.

 

Thanks for all advice. I will check all the things listed above.

By the way, what exactly is the "pinion yoke"? :confused:

 

I think the front differential bushing also. Any good suspension / allignment center should be able to help you with the problem. The IR rear suspension on your car was on all 63-82 Corvettes, so it is not a rare or hard item to fix.

call ZIP CORVETTE in Mechanicsburg, Va for help with someone in your area. They have been selling parts since the 70's and should know good service people in your area. Also, look at http://www.ncrs.org for the Mid Atlantic NCRS Chapter people in your area that can help.

 

The pinion is the small gear in the differential that drives the bigger "ring" gear. The pinion shaft runs out the front of the differential and the driveshaft U-joint yoke bolts to it. The bushing right under the yoke gets broken down over the years from torque action and starts banging or thumping when starting off or shifting gears. And that's about all I know about it! :steering:

 

Yeh ,i've been through the missing shim routine after alignments. You have to use non slotted captured shims, which alignment people hate ,or install a 6" cotter pin through the pocket and shims to hold them in place. Not all mid years have the pockets drilled for the cotter pin. I know the 67 does not but not sure when they stopped drilling and went to captured shims. If you have a numbers matching ride you probably don't want to drill the pockets but have it aligned with the captured shims. You'll have to find a good alignment shop in your area thats into corvettes and will take the time. Forget about Chevy dealerships they are usually as bad about doing it right as all the rest of the chains. Check out the rest of the rear suspension as advised in the other posts, there advice is right on. LOL
Bob


[Modified by Desertvette, 1:30 PM 8/27/2003]

 

OK, so what are "captured shims", and why do alignment folks hate them?

I think I must have had slotted shims before, since the ones that fell out were open at one end.

Thanks again for all the info. I'm learning as I go along here!

 

I think captured shims have holes in them, not slots. People hate them because you need to remove the trailing arm pivot bolt to move/add/remove them when adjusting rear toe-in whereas you can do the same things with the bolts on with the slotted shims.


[Modified by brucep, 8:08 PM 8/26/2003]

 

That's right, brucep has answered your question perfectly. If you buy a set of shims from Zip one side is slotted and the other is a drilled hole. [I mention this since God knows what you'll find installed ,if your car was like mine]The shop should do the alignment with the slotted side to set up and when done turn them around and reinstall through the hole for a secured job. That way you won't be throwing shims every time you hit a bump.
Do a search in the archives and you can probably find out when they stopped drilling the pockets. If the pockets drilled this setup works well also and is more convenient for those doing the job. LOL
Bob



[Modified by Desertvette, 1:34 PM 8/27/2003]

 

A agree with Dansyellow66. Here is a sure fire way to verify that is where the problem is. Jack the car up enough so you can get under the differential support. Push up on the tounge. That should be the sound your hearing. Their are two bushings there, one you can see which seldom wears out and then the one on the top you can't see (most likley cuplrit). I'm planning on doing this to mine and have been told that you can't take it off without first removing the drive shaft.

Changing the differential fluid? If you go this route I'll share something I heard and this board should be able to verify. When changing the fluid pass the old fluid through a coffee filter and put it back in. First 90 weight gear oil seldom wears out especcially in a closed system like the rearend. Second is the most important. Original gear oil had an additive that came from the sperm whale and is the best lubricant. The enviromentalist got GM to use a synthetic now which in no way gives you the protection of the original additive. Any commets about the Sperm Whale theroy?

 

You can do it with the driveshaft connected - it will take you a few minutes and some arb scratches to figure out how to get a wrench situated just right.

The torque of the half shafts force the whole differential to rotate (carrier bracket towards body) under rotation. This is definately a place to check for clunking - be sure to check the torque settings on this bolt - the snubber cushions really get smashed!

Brian