Trailing Arm Shims Total thickness

[Patrick N.]

I am shimming my trailing arms (C3) to get the initial alignment prior to having the alignment done professionally. TA are new, I am planning to add equal shims on both side of the arms for now to get it clsoe. (Leaf spring is not installed yet).

My Question: Is there a maximum combined thickness that the shims should not exceed? I thought I read something about at one point but not certain.

Thanks
Pat

[Gene M.]

Re: Trailing Arm Shims Total thickness

Pat,
I don't think the total thickness is a requirement. The fact that what ever number and thickness you use that it must be tight "stack up" to fill out the spacing on each side of the trail arms.

I insure it is snug by tapping in the last shims with a small hammer. Be sure to have a good assortment of thicknesses to achieve a good alignment at the alignment shop. "Split" size shims may be required from what you initially installed so bring extras.

[Terry M.]

Re: Trailing Arm Shims Total thickness

There may be a maximum thickness called out in the AIM -- I know there is for the front shims, but with rebuilt arms I am not so sure the maximum Chevrolet used for new parts is applicable now forty years on.

[Patrick N.]

Re: Trailing Arm Shims Total thickness

Thanks Gene,
This is my second attempt at this, I initially shimmed it on my last go around and I raised the TA so the wheel is ride hide following the dimensions in the AIM. After stuffing the inner pocket, then outer (tapping last shim in with hammer). I lowered the TA and the wheel was toe-out by greater than 1/8".
I am curious if that is expected with no body or leaf spring installed or did i simply do it wrong? (I assume the latter) any thoughts?
I searched other past threads on this and plan to follow suggestions to shim equally and let the alignment shop get it dialed in correctly.

Thanks Again
Pat

[Gene M.]

Re: Trailing Arm Shims Total thickness

Thanks Gene,
This is my second attempt at this, I initially shimmed it on my last go around and I raised the TA so the wheel is ride hide following the dimensions in the AIM. After stuffing the inner pocket, then outer (tapping last shim in with hammer). I lowered the TA and the wheel was toe-out by greater than 1/8".
I am curious if that is expected with no body or leaf spring installed or did i simply do it wrong? (I assume the latter) any thoughts?
I searched other past threads on this and plan to follow suggestions to shim equally and let the alignment shop get it dialed in correctly.

Thanks Again
Pat

At this point it sounds close enough to get to alignment shop. There is no easy way to know if all toe is on one wheel or a split until its on the machine. If the body was off and you did this you could set it (toe) relative to centering of the frame. It sounds like you know what you're doing and making it easier for the guy aligning your car.

[Larry M.]

Re: Trailing Arm Shims Total thickness

I am shimming my trailing arms (C3) to get the initial alignment prior to having the alignment done professionally. TA are new, I am planning to add equal shims on both side of the arms for now to get it clsoe. (Leaf spring is not installed yet).

My Question: Is there a maximum combined thickness that the shims should not exceed? I thought I read something about at one point but not certain.

Thanks
Pat

Pat:

When rebuilding the trailing arms on my 1967 car, I found that the (likely) original shims were 13/16 inch total. After rebuilding by Bair's, I found that only 3/4 inch of total shims were required. This is a difference of 1/16 inch......I think Joe L indicated awhile back that the newer trailing arm rubber bushings were a bit thicker than the originals.

I my case, I was able to count the old shims that I took out, and I replaced with a similar amount (less 1/16 inch) when installing.

I still have to do my final rear alignment. Meanwhile the shims that I installed and the alignment are close enough for short driving trips.

Larry

[Patrick N.]

Re: Trailing Arm Shims Total thickness

Thanks everyone,

I hear what you are all saying with the rebuilt TA and new rubber effecting total shim sizes.

I will do the re-shim again and if no real change, it will be good enough to get to the shop.

BTW, I did go with the slotted stainless shims per Joe L and a few others comments. Sure it may take a point deduction or two, but it sure is easy to set up and will look good down the road.

Thanks again guys,
Pat

[Patrick H.]

Re: Trailing Arm Shims Total thickness

Have extras of the thinnest shims, if possible.

When I brought the orange car in for alignment I had all the factory shims back in place. I also brought all the stainless spares I had. The alignment guy used all my spares + got a few from another alignment guy at their other store to correctly align the car as he best saw fit. So, a few more brought with the car can be very useful.

Patrick

[Ken P.]

Re: Trailing Arm Shims Total thickness

I got really lucky when I did my 72's trailing arm bushings. I just shoved every shim that I could get back in and took it for an alignment. Tech said and printout showed that it was right on the money. They only added one small shim to the front right and I was good. Should have plaid the lottery on the way home.

[Timothy B.]

Re: Trailing Arm Shims Total thickness

When I have done this I always stringline the outside of the car. Just wrap a piece of fishing line around to the outside of the rear tire and carry it to the front past the tire and pull it snug on something like the stablizer link. Roll the car so each tire is on two pieces of floor tile as this acts like a bearing and adjustments can be made with the suspension normalized.

Make sure the line is in the center of the tire/rim in both front and back then move (steer) the front tire to where there is no gap between fishing line and tire in front or rear of the front tire (front tire exactly straight ahead).

Go to rear and with fishing line touching the rear of the rear tire shim inside stack so front of tire is 1/32+- from touching line. You will be surprised how good you can do. In some cases it may be better than a $100. alignment. Make sure the front tire is straight ahead, very important..

After you finish rear, set front toe with steering wheel in straight ahead position and the front tires with 1/8" toe in. Go for a ride and when driving straight on a LEVEL road see if the steering wheel is straight. If it's not make a correction to BOTH front adjustment sleeves in the correct direction to get it perfect.

Very easy to do and lots of info in archives. Take the $100. and treat wife to dinner, cheap insurance for the next time she gets mad at you.

[Patrick H.]

Re: Trailing Arm Shims Total thickness

When I have done this I always stringline the outside of the car. Just wrap a piece of fishing line around to the outside of the rear tire and carry it to the front past the tire and pull it snug on something like the stablizer link. Roll the car so each tire is on two pieces of floor tile as this acts like a bearing and adjustments can be made with the suspension normalized.

Make sure the line is in the center of the tire/rim in both front and back then move (steer) the front tire to where there is no gap between fishing line and tire in front or rear of the front tire (front tire exactly straight ahead).

Go to rear and with fishing line touching the rear of the rear tire shim inside stack so front of tire is 1/32+- from touching line. You will be surprised how good you can do. In some cases it may be better than a $100. alignment. Make sure the front tire is straight ahead, very important..

After you finish rear, set front toe with steering wheel in straight ahead position and the front tires with 1/8" toe in. Go for a ride and when driving straight on a LEVEL road see if the steering wheel is straight. If it's not make a correction to BOTH front adjustment sleeves in the correct direction to get it perfect.

Very easy to do and lots of info in archives. Take the $100. and treat wife to dinner, cheap insurance for the next time she gets mad at you.

I just pay the guy to do it while I take the kids fishing.

[Tom L.]

Re: Trailing Arm Shims Total thickness

Tim, glad to hear you have success with this. I raced late models years ago and re-aligned the car weekly including camber, caster and bumpsteer (a real PITA and hope I never have to do it again!). Still have the tools or access to them.

We always found a centerline on the car, for older ones that were banged around, or strung the car using the frame rail as a refrence similar to the way that you describe. Doing this reduced problems with the front and rear tires not tracking perfectly.

Being straight axle cars we didn't need to worry about camber and castor, except when using a cambered rear, we simply put it where it needed to be. Clearly these cars have been around and often banged around.

My question is are there known refrence points on the rear of the chassis that can be used to find a centerline? I'd like to use the front trailing arm mount but plumb-bobs can't be dropped straight down from them. Thanks!!

[Timothy B.]

Re: Trailing Arm Shims Total thickness

Lynn,

I too have used the frame side rails to stringline the car to eliminate the tires rubbing the stringline etc. Then I measure to the rims forward and back on front/rear to measure. I have found this method a little more time consuming and the results are pretty much the same as the method above. It's probably the better way to string the outside if the rocker panels are off and you can get to the frame side rails.

As far as finding the centerline of the frame and measuring, that is the best way to do the alignment but good luck trying to do this with everything attached on a completed car. It's possible I guess but the chances of getting something wrong IMO out way the other method.

I enjoy doing this myself because you learn and in many ways your work is better than a shops work.

[Tom L.]

Re: Trailing Arm Shims Total thickness

Doing it yourself does add to the fun. For myself, I haven't done an alignment in a while but I'm fortunate enough to have all the tools like the camber/caster gauge, good straight edges, and digital turn plates to allow the suspension to move after making adjustments. If you don't have turn plates grease between floor tiles or glossy papered magazines work. That's what we used before we could get out sponsors to buy us all the goodies. Thanks!!