S.O.S. Rear wheel alignment kicking my a$$
 

I'm attempting to set the rear wheel alignment on my car using the Duntov Motors method outlined here:

http://www.duntovmotors.com/tech-alignment.php

The camber on both rear wheels is set to -1 degree.

https://cimg7.ibsrv.net/gimg/www.cor...f5d965902f.jpg
https://cimg3.ibsrv.net/gimg/www.cor...bd37fb5814.jpg

Using the string method outlined in the procedure where you run a string around the back of the rear tire, forward to where its just touching the front of the rear tire, and then measuring the distance from that extended string to the center of the front hub, I have exactly 3 and 6/32 inches on both sides....telling me that the track is even.

https://cimg0.ibsrv.net/gimg/www.cor...3e398e30fa.jpg

My problem comes in as I'm attempting to set the toe in the rear. Using my toe plates, I'm showing 66 and 15/16 inches side to side on the front of the tires and 66 and 6/16 at the rear, giving me 11/16 toe out where I'm looking for 1/16 - 2/16 toe in. I'm at the point on the drivers side where the entire stack of shims is on the outboard side of the trailing arm, so I have no further toe in adjustment that I can make on that side. Further adjustment on the passenger side could bring total toe in closer, but the track would then be off in the rear.

https://cimg0.ibsrv.net/gimg/www.cor...05e2b67357.jpg


Any assistance would be hugely appreciated!!

Thanks
-Greg

Greg:

Not certain I can help you solve this problem this afternoon, but I have a few comments:

1. If you cannot make the rear toe adjustment by adding and subtracting shims, you may have a bent frame or trailing arm. On my lo-mile 67 car, my shim pack is about even on both sides of the trailing arm for both arms.

2. Rear toe is not measured like front toe. Front toe is simply front of tires to rear of tires difference. Then you set the steering wheel position to be correct with the tires pointing directly forward. You adjust the tie-rod adjusting sleeves evenly to get the steering wheel into the correct position and still maintain the correct toe number. The rear toe is measured for each tire and is referenced from the chassis exact centerline. You can use your front to rear strings to establish this chassis centerline and then measure and adjust each side independently.

3. A commercial 4 wheel alignment machine will find this chassis centerline and then provide the toe reading based on that. Doing it in your garage, that is your mission to find this center point. I have read a lot about how to do this, but have not done it myself. I took the easy way and paid a good local guy with a new modern Hunter machine to do it for me. I told him I would make the corrections in my own garage, since I have the two-hole shims. Passenger side was right on, but I have a 1/8 inch correction to make on the Driver side..........it is about 1/8" toed-in more than the spec. This is actually visible to me from looking at the rear and driver side rear positions. So I still have my own work to do.

4. Suggest you read up on establishing the frame centerline so you can then use this reference. Alignment on one side of your car rear may be fine and the other may be an issue due to mechanical damage. But then you will know which is which.

Best I can do right now.

Larry

Wow - 11/16 total toe out. You should be able to see one or the other wheels looks wonky when sighting down the side of the car I would think. What I do is get a good 4 or 5 ft. straight edge and lay against the sidewall of the tire and extending forward along the string line. Pick a distance off of the center of the tire and get a measurement to the string line on both sides at equal distance. Be sure the front wheels are pointing straight ahead. You can probably check this by also laying the straightedge against the front tires and checking it to the string line. But if the rear tires are turned in or out much, it can throw this off a little and you may have to check and make small corrections in a multiple step process.

Stock - track is about .8" wider in the rear on a Corvette so you will probably be shooting for about 1/8 to 1/4" on both sides to the string to get the wheels pointing straight ahead. You have custom wheels so offset and track could be a bit different on your car. The straightedge will be on the outside of the string. As far out as yours appears to be right now you may have one side where the straight edge runs way outside the string line. Shim to try to get it equal on both sides.

Then use your plates to measure your toe in/out. Make equal adjustments in shims on both sides until the toe in is where your want it and the distance from the string line to the straight edge is equal on both sides. Should be good then but I've found the key to a garage alignment success is to double check and repeat everything. When it check out the same twice then it should be solid.

If you are running out of shim room then something would appear wrong or bent.

Good luck

Thanks guys. I'll have to reexamine. I seriously doubt anything is bent as the trailing arms are brand new Global West trailing arms, and this car had a frame off restoration done between 1978 and 1982...and has been driven 578 miles since then. Thats not to say that they didn't start with a bent frame, but I don't think thats likely.

Alignment
 

Another way to find the center line of chassis is to take a string with a key ring on one end. Loop it around lower ball joint in front. Extend string forward about 3 feet and mark arc on garage floor. Then extend back behind front suspension and mark floor. You now have 2 reference points. Tape down a string , lay out flat. That will give you the center line.

I find it hard to believe the shims are all stacked one one side. Eyeballing it will show you are off if its that much.

So just to verify I'm not losing my mind, I went back out to the garage...

Assuming that the metal trim that runs the length of the rocker is (relatively) parallel to the center line of the car, if the tires were tracking straight, that line of string running around the rear of the rear tires, and just touching the front of the tires would be parallel(ish) to that rocker if the tires were pointed straight.

Not surprising, that string on both sides of the car is 2 and 3/32nds from the rocker trim just in front of the rear wheels, and 3 inches from the trim just behind the front wheels. This at least confirms that both wheels are currently toed out pretty much evenly.

Like I said before, the driver side has the entire shim pack on the outboard side of the trailing arm, and the passenger side is similar, with the only inboard shim being a single medium shim.

I'm really at a loss as to how I can be maxed out on adjustment with this much toe out :banghead:

C2 rear alignment woes
 

Greg, I feel your pain as I'm experiencing similar problems.
I tried finding centerline, strings, laser and gave up and took to an alignment shop, told him what I wanted and he came back that I had 3/4" toe-out and he couldn't get it any better. After more measurement with strings I determined that it was really 3/16" out. He didn't know how to set his machine up for inches instead of degrees. :( BTW, the guy had to call a service rep to find out how to set machine for inches instead of degrees. It was a simple set up screen.

In comparing my new trailing arms and bushings to my originals I found that the new bushings are thicker/wider than the old ones. I suppose there could be some differences between the actual trailing arms too. After having them shaved down I'm still at 1/16" toe-out on drivers side. I can get correct toe-in on the passenger side though. I haven't done any corrective measures yet though.
Gary
PS As original owner I know the car has not had frame damage.

Doing an alignment in your garage can be a pain without the tools like an alignment shop has. As stated above the best way to set toe is with a laser system or a string system that is set off the centerline of the car. This ensures your thrust is correct and that toe is set relative to the centerline of the car. We make a set of tools that makes this process much easier with built-in turnplates, toe bars, etc... You can check us out at: www.CSMPerformance.com . We'd be happy to help with any alignment questions/challenges!

Thanks!
Colton

Well, the other equation in this is the half shaft length. Since you have a custom frame and so forth that I no nothing about - is it set up to run with standard C2/C3 length half shafts? Or is it set up to run with a slightly longerr, custom half shafts and strut rods to bring the outboard hub outward and allow wider track?

No custom anything here....all stock suspension with the exception of Global West control arms.

Yup, this is exactly what I'm trying to avoid by dialing the rear in myself. I don't trust most alignment shops to know what they're doing when it comes to these cars. I did notice that the Global West bushings are slightly thicker than the factory bushings, but not to the point where you don't have enough real-estate in the pockets to at least get the tires pointed straight ahead.

C2 original trailing arm bushings vs aftermarket.
 

Greg
I just went out to the garage and measured my original trailing arm/bushings to an Ikerd trailing arms (from original GM dies) with bushings installed. With a digital caliper the originals measured 2.107 inches and the Ikerd's were 2.308 inches. The ones on my car are still on and I haven't measured them at this time.
Gary

OK - skimmed over your build thread and see I was mistaken in assuming you were using an aftermarket chassis. Very nice car you started with by the way. I assume the car had a good alignment when it was still stock and it appears the main thing that has changed that would affect the alignment in any way are the trailing arms. So I would say there almost has to be something wrong with their fabrication or they are intended for use with an aftermarket frame or something. I think I would contact the supplier and see what they have to offer on the subject.

Thanks. Yes the car is very nice, I have however found that it clearly was not used much after being restored back in the day....many things are not tight, adjusted, etc. I plan on calling Global West on Monday to get their thoughts. They make a quality product, and I know others have used GW products without issue.

The rear toe-in set up used on my car after trailing arm bushing replacement was slightly different than the Duntov method.
A 10 foot string line was set up at mid wheel height a few inches away from the wheel rims. The idea was to parallel the front and rear wheel rim edges to the same dimension, say 3 inches. The steering wheel was adjusted so the front wheel rim edges and the rear wheel back edge read the same dimension. The front edge of the rear wheel dimension from the string line was measured for toe, in or out.

Starter shims on both sides of the trailing arm bushings were installed as a set point. Reading the dimension directly from the string line to the front of the rear wheel rim edge, already installed trailing arm shims were were adjusted from one side of the bushing to the other, accordingly. Using 2 hole shims, double checks, etc., the best end result that was achieved came in at 1/16 toe-in on both sides.

John

One thing that may be causing problems is differential yoke wear. As the yoke ends wear internally against the pin, this effectively shortens the track at the rear wheels and increases toe-out. To check, pull the top of the tire in and out while someone watches the inner yoke move. Only 1/8" of wear on each side will change rear toe by ~1 degree!

hmmm....Ill have to look into that one. Thanks.

Verify the offset of each control arm.
https://cimg7.ibsrv.net/gimg/www.cor...b736cccdee.jpg+

See this thread - in particular post #3, 10, 11 and 19
https://www.corvetteforum.com/forums...t-at-home.html

""The camber on both rear wheels is set to -1 degree.""???

Why do you need so much negative camber??? Are you running bias ply tires??? I am adjusting for 0 deg on R66 with radials.

I am in the middle of aligning R66. I had too much camber and couldn't adjust it out. I installed new spring bushings and about 1/2" spacers. Guess the spring is weak. I also found the weight of a full tank of fuel affects the camber and toe. This gives me enough adjustment that I can now achieve the 0 deg camber I am trying to get. I am still working on the camber and have not yet gone after the toe. I found that you must have the camber set before you try to set toe.

Ron

I had the same question - I usually shoot for 1/2 deg. But I figured it was possibly an alignment setting for track use or something. But I don't think it's a factor in getting the toe dialed in as long as he working at loaded suspension, static vehicle height.