Trailing Arm Shims

[Ed S.]

Question regarding the depth of the "slot" at the one end of replacement / repro trailing arm shims.

Is the base of the slot, the "U" at the bottom of the slot, the same distance from the edge of the shim as the base of the hole on an OEM '64 shim? In other words, are the slots cut deeper or longer into the shim than the position of the hole in an un-slotted shim?

I have a bunch of non slotted shims (2 holes). I need to have an alignment. I am wonder if I can just cut "slots" into one end of the shims instead of buying a set of slotted shims for $50 plus shipping. If the slot length or depth is the same as the hole placement I see no reason to not cut them at one end.

It is hard to tell for sure but.... looking at pictures of shims on vendor websites, the "slots" seem deeper or longer than the position of the holes.

[Alan D.]

Re: Trailing Arm Shims

Or just use all the 2 hole shims with the exception of 1 or 2 made up slotted shims on each side, slide those into the middle of the shim stack so nobody can see.
I assume you have a reasonable idea of what is needed, if not this trick may not be the best way to go. Since you have a bunch of 2 hole shims which were standard on 64's making them slotted on one side will work fine, for the depth is already set for a 64

[Ed S.]

Re: Trailing Arm Shims

Alan, thanks for the comment. One more question, your opinion please. I was thinking of cutting the "slots" on one end so that the orientation of the slot is perpendicular to the shim, i.e. rotated 90 degrees from a normal slot. If I did this I or the mechanic could "hook" the shim over the bolt and it would be less likely of sliding down and out. Thoughts?

[Jim D.]

Re: Trailing Arm Shims

Here's pics. of my original 65 shims and S.S. slotted ones. The nice thing about the slotted ones is that they allow the shim to be able to drop into the pocket so that once the bolt is tightened, there's no way they can come out and you don't need to drill the pocket for a cotter pin.

[Edward D.]

Re: Trailing Arm Shims

Without the cotter pin slotted shims can move when trailing arm pivots and subsequently come out, that's why GM put the cotter pin in there, its a safety thing. All C2s originally used two hole shims that are captured by the pivot bolt. I have seen these hook cut by alignment shops before. If all you are doing is adding a shim than this can save you the trouble of removing the pivot bolt but I cannot recommend doing so. Even more dangerous is using a short slotted shim pushed partway in to line up with the rear hole of the longer 2 hole shim. These likely will drop out on the road. If you want originality go with the two hole shims and do the work of pulling the pivot bolts to install. A good tip here is to setup the toe using slotted shims then remove them and replace with the same thickness shim packs of the two hole type. That way you don't need to keep pulling the bolts to change shims when setting up. If the car is a driver or the point deduction is not important to you go with the slotted shims, tuck the ends into the pocket, and drill the cotter pin hole. Not many alignment shops left that will take the trouble to do the rear toe properly left.

[Gary J.]

Re: Trailing Arm Shims

I have had good luck with slotting the C2 shims like this. No reason they should fall out like the C3 when the cotter pin is not used. To me it is better that removing the bolt to add or take away shims, saves time too especially its the alignment guy.

[Ed S.]

Re: Trailing Arm Shims

Jim, Edward, thanks for the comments and pictures - I see that cutting slots would not be a great idea after all. Thanks again - greatly appreciated.

[Ed S.]

Re: Trailing Arm Shims

Now that is an interesting approach. Thanks Gary. I could see how that would work.

[Gene M.]

Re: Trailing Arm Shims

Ed Dupere is 100% correct. I’ve seen plenty of Corvettes with lost on the road shims. They will move as he stated and dislodge with any spirited driving.

What is the big problem in installing the correct 2 hole shims as original, it not like your going to do this as a weekly maintenance?

[Jim D.]

Re: Trailing Arm Shims

I too have seen lost shims from poor workmanship. The only way a shim could come loose the way I do them is for the pivot bolt to be loosened enough for the shim to be tapped forward, pried upward and then pulled out the back. I've never seen it happen in the 40+ years I've been doing alignments.

[Joe L.]

Re: Trailing Arm Shims

As I mentioned before, I've exclusively used the slotted style shims on my original owner 1969 for about 40 years. I've not tucked them down into the frame pocket for the vast majority of that time and I've never used the cotter pins (although my car does have the frame holes for the pins). I have never lost a shim. Ever.

[Frank D.]

Re: Trailing Arm Shims

The poly front T/A arm bushings a prior owner used on my 63 disintegrated completely and with the slotted shims tucked in I didn't lose any....if they weren't I can't say that I'd have lost any, but it certainly would increase the odds...

[Alan D.]

Re: Trailing Arm Shims

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.

Is all this work worth it -------------- hardly ----------- best to loose a judging point or two !!!