Initial Trailing Arm shim set up

[Mark S.]

I have read much debate on what type of shims to use and the "tricks" to align but have not seen too much on what the initial setup should be when reassembling after a full body off when starting with a bare frame. Most of what i have seen is that one should use an equal shim stack on the inside and outside of trailing arms then get an alignment after the car is back on the ground and running.

Assuming this is the best starting point how tight should the stack be? Should I stuff as many as possible so there is little lateral movement or give a little space to allow for some sideways movement? I have Dec 68 1969 car and will go with the original 2 hole shims.

Thanks as always for the help...

Mark

[Patrick B.]

Re: Initial Trailing Arm shim set up

The best starting place would be the same shim count it had prior to disassembly if you recorded it. If the new bushing is a different width from the original, add or subtract equal shims from both sides of the trailing arm bushing.

[Larry M.]

Re: Initial Trailing Arm shim set up

I would use the slotted shims for the initial alignment........and then replace later with the exact same 2-hole shims. This is easier and better for all concerned: you and your alignment mechanic.

When installing shims at home, the LAST shim goes in tight, and requires a small hammer to tap it in place. Then the "thru bolt" is tightened/torqued and cotter pin installed.

You can pretty well "eyeball" rear camber in your garage. You want the tires to be straight up/down or slightly negative (pointed inward) by 1/2 degree. Many of us use an angle finder and a piece of straight wood or steel against the wheel to get close.

Same for the rear toe-in. You want the tires to basically point straight ahead.....or slightly inward. If you are a little bit off initially, this is okay, as it will be corrected on the alignment machine. Ultimately, I believe, you want about 0 to 1/32 inch toe-in on each rear wheel.

You can get fancier with a taut measuring string around the car to reference toe, and something like FAS-TRAX to set camber............but it you are just driving a few miles to an alignment shop, what is the need??

Larry

[Frank D.]

Re: Initial Trailing Arm shim set up

I didn't have much luck with the DIY alignment, I got the toe in at the rear close because I preserved the shim pack stacks and reinstalled them precisely when I put in the rebuilt trailing arms on the 63. I "settled" the suspension and used the Lars method for camber adjustment in my garage and it was so far off it was pathetic (maybe its just me) - I trailered the car the 12 miles to the only alignment shop I trust.

[Mark S.]

Re: Initial Trailing Arm shim set up

I appreciate everyone's input. All helpful. I did record the chassis tear-down but everything was such a mess I can't really use that for much. All the thin shims were completely rusted out and essentially gone, the strut rods were bent and the strut rod bracket was badly bent. So i now have all clean straight original parts and new trailing arms with a correct build using GM bushings.

Does anyone think that starting with an equal thickness original shim pack and leaving a little space to slide in some slotted ones in between at the alignment shop could work too?

[Larry M.]

Re: Initial Trailing Arm shim set up

If you drive the car, the shim pack needs to be tight.

Larry

[Frank D.]

Re: Initial Trailing Arm shim set up

If you drive the car, the shim pack needs to be tight.

Larry

Yes, the trailing arms are subject to rotational torque and any "slop" will not be good for your front bushings...

[Richard G.]

Re: Initial Trailing Arm shim set up

I am not advocating this system. But I bet you could use it or something like it to rough in your alignment.

https://www.youtube.com/watch?v=unOu31Mz7OA

The QuickTrick Wheel Alignment system is $300 give or take a few $.

This is likely closer to what may be useful information;
How to Set Up Corvette IRS Rear Camber(basic do-at-home version)
http://corvette-restoration.com/wp-content/uploads/technical_papers/Set_Rear_Wheel_Camber.pdf

Rick

[Frank D.]

Re: Initial Trailing Arm shim set up

I am not advocating this system. But I bet you could use it or something like it to rough in your alignment.

https://www.youtube.com/watch?v=unOu31Mz7OA

The QuickTrick Wheel Alignment system is $300 give or take a few $.

This is likely closer to what may be useful information;
How to Set Up Corvette IRS Rear Camber(basic do-at-home version)
http://corvette-restoration.com/wp-content/uploads/technical_papers/Set_Rear_Wheel_Camber.pdf

Rick

That last document is the Lars method using a piece of sheet metal over rods as skid plates along with a straight edge and angle gauge to do the camber adjustment in the rear.
I tried it, it didn't work worth a hoot for me.

[Richard G.]

Re: Initial Trailing Arm shim set up

Frank
That is good to know as I never attempted it myself.

I would recommend a professional 4 wheel alignment with a modern laser alignment equipment after getting it close as you can using what every method you can.

I can attest to how difficult it is just to push a Corvette when it is out of alignment.
Rick