63 trailing arm shims keep falling out

[Joe T.]

I'm looking for the most common reason(s) for my passenger side trailing arm shims to keep falling out( 3 times)
The trailing arm looks in good shape, the car has an occasional clunk in the rear after going from forward to reverse, to try to solve this I have had it checked multiple times by a Vette shop and have also put in new posi unit new ring and pinion, had all U joints checked. I'm wondering if it has something to do with the trailing arm bushing, trailing arm bearing or the drum brakes. Frustrated, joe

[Joe L.]

Re: 63 trailing arm shims keep falling out

I'm looking for the most common reason(s) for my passenger side trailing arm shims to keep falling out( 3 times)
The trailing arm looks in good shape, the car has an occasional clunk in the rear after going from forward to reverse, to try to solve this I have had it checked multiple times by a Vette shop and have also put in new posi unit new ring and pinion, had all U joints checked. I'm wondering if it has something to do with the trailing arm bushing, trailing arm bearing or the drum brakes. Frustrated, joe

Joe------


Usually, the reason is that the shim pack is not tight enough. The final shim should be driven in with a hammer. If the final shim is a thin shim, then remove the thickest shim, insert the thin shim and then drive the thick shim in with a hammer. Then, tighten the nut to spec (with the suspension normalized).

Does this car still have the original 1963 style shims or later style shims?

[Edward J.]

Re: 63 trailing arm shims keep falling out

Joe, one of two things come to mind, there is not enough shims to keep the shims in place once tightened. If you loosen the though bolt see if you a space to install another shim. That bolt and nut have to be really tightened.to keep shims in place.The noise in the rear, check the snubber bushing they have been know to compress over time or worst the rubber splits and falls out causing shifting when going back and forth. The other thing is the rubber cushions and been known to fail.this supports the rear diff.on each side.

[Joe T.]

Re: 63 trailing arm shims keep falling out

the original style and mechanic said he beat last one in with hammer

[Alan D.]

Re: 63 trailing arm shims keep falling out

As I recall the 63 used for a short time slotted shims then went to the long 2 hole (please confirm if that's so, I'm not a 63 person)
Here is another little trick a member (Ralph) did,

1. I welded the arm onto the 1/4" shim only. I then drilled and tapped a 10-32 hole in the center of the shim so that I could attached thinner shims to it "as needed" via a drilling a clearance hole in the thinner shims and attaching them with a 10-32 screw. In affect; the shim pack was sandwiched together with a screw which is NOT visible when it's buried inside the frame cavity.
2. Because I had access to a machine shop; I was able to do the "slotting" in Bridgeport milling machine; however, this could be done with a hack saw. All shims in the "shim pack" must be slotted, the thin ones area bit more difficult to do.
3. Sketch attached showing modification.
4. Picture of actual shims attached ------ the one on the left is a 63-67 shim which had been slotted and has the 10-32 hole for the thinner shim containment, the one on the right is a 67 & up shim.
5. Due to variation I highly recommend making a modified shim identical to my sketch out of 1/4" plywood to make sure it works before making it out of steel.
6. Some guys simply do the slotting with OUT the arm ---------- this will work perfectly; however, you are at great RISK because they have been know to loosen and fall out while driving !
7. This worked out perfectly for me because it met the NCRS 1966 requirement PLUS the guy who performed my rear alignment had no problems removing the shim pack without removing the training arm bolts. Note: I slotted and drilled plenty of extra shims for him to get the desired shim pack thickness he needed to align the car.