Rear Toe-in alignment with the body off the frame HELP!

[Louis C.]

I'm doing a body off restoration on a 66 and have replaced the trailing arms (USA made supplied by Ikert's years ago). I initially set the shims up identical to original but found the tow-in was way off. Nearly an inch towed in. To get a measurement I flipped the rotors and measured from the front to rear of the rotor. The frame was first leveled, followed by setting the camber at zero, ride height set, no spring.

To get it close to where it needs to be I had to remove all outboard shims on both sides (can't be right). and still have a total of 3/16" and that is still too much. Tried to verify to the front so I set the front at zero-toe in and matched the front width to the rear of the rear rotor width, strung a string to verify what I was measuring.. Still seeing same thing. 3/16" total (1/16" left and 1/8" right)

I'm trying to get the rear toe-in close enough so that when I finish the restoration and take the car to an alignment shop they won't have to mess with the shims. For no other reason other than they won't want to swap shims and honestly, if it was doing the alignment I wouldn't want to do it either.

[Steve G.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Do you have the outboard strut bolt/shock mount all the way in? I ask that because the problem could be that they put the arms together with the bearing supports on the wrong side. You would be able to tell that by the flat in the one side of the through holes for the strut in the support being on the wrong side when the shock mount bolt is on the correct side.

I have a 67 in my shop now where it was assembled like that. They also couldn't bolt wheels with tires on because the tires hit the trailing arm.
Steve

[Duke W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

You need to measure the toe of each wheel relative to the frame centerline.

Place a piece of masking tape in the vicinity of the cross member centers, Use a good carpenter's tape to measure the centerline of all the cross members and a fine point pencil to mark them on the masking tape. Then check that all the centerline marks are along the same straight line, which they should be.

With the wheels/tires installed, block up the rear ride height to the "D" dimension described in the CSM and AIM.

Run a string along the centerline you measured. Use plumbobs to establish the height of the string across the OD of the tires at the axle centerline or as high as you can get it without interfering with anything.

Mark the rear tread face of the tire with a good reference point from which you will measure at the axle centerline height or the height of the string.

Measure the distance from the centerline string to the tire reference point.

Now rotate the tire 180 degrees so the tire reference mark faces forward and take another measurement. Shim so that this measurement is 1/32" less than the first. That is 1/32" toe-in on that side.

Do the other side the same way.

This should get it pretty close. Use at least a couple of 1/32" shims at each of the four locations. Since the trailing arm radius is about double the tire radius (13.5-13.7" for OE equivalent tires), swapping a 1/32" shim from the inside to the outside will change toe by about 1/64".

Install a thick shim last and it should be snug enough that it takes light tapping with a hammer to get it in.

If the above doesn't work then there is either something wrong with your measuring techinque, something wrong with the trailing arm bushing/installation, or the frame is out of square beyond OE tolerance.

You can't be too careful doing this, so for a first timer, double or even triple check all your measurements before proceeding to the next step.

[Michael W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

To get a measurement I flipped the rotors and measured from the front to rear of the rotor.

This might be part of the problem. The rotor mounting surface of the spindle is not usually perpendicular to the bearing surfaces. GM machined the rotor faces after installation on the spindle to eliminate runout- meaning that the rotor surfaces would no longer be parallel to the wheel mounting flange.

By flipping the rotor over, the rotor surfaces might be way off what you're expecting them to represent.

[Joe R.]

Re: Rear Toe-in alignment with the body off the frame HELP!

First, Pat Ikerd has done more trailing arms successfully than the entire population of the NCRS so don't go down that road! Pointing fingers in the dark will not get your trailing arms aligned! That is just wasting time getting at the real problem.
Try Duke's method and see what you find.

JR

[Michael W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

I have no doubt but note that the OP's rotors are not riveted to the spindles as per normal practice. Perhaps the OP has sourced his own?

[Michael W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

I'm trying to get the rear toe-in close enough so that when I finish the restoration and take the car to an alignment shop they won't have to mess with the shims. For no other reason other than they won't want to swap shims and honestly, if it was doing the alignment I wouldn't want to do it either.

Are you using the two hole shims or the later slotted type? I'd suggest the latter for ease of present and future alignments.

[Louis C.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Yes, it is in all the way and the shocks are mounted.

[Duke W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

What's all this talk about rotors? Toe, in inches, has to be measured from the OD of the tires.

Duke

[Dan B.]

Re: Rear Toe-in alignment with the body off the frame HELP!

It's a waste of time trying to do this without the tires or rear spring in place and the vehicle at proper curb weight. With new bolts, T-arms already serviced, and new shims, it should be pretty easy to do at the end. Dan

[Duke W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

It certainly is NOT a waste of time to set the toe as I described in post #3. If fact it's the easiest way to set it up with simple tools prior to putting the body back on the frame.

The reward is when the car is finished, you put it on an alignment rack, and find that it needs no adjustment.

Duke

[Mike E.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Plus installing non-slotted shims in a midyear can be a total pain when the body is back on. Most alignment shops won't want to mess with the correct type of shims.

Mike

[Dan B.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Not disputing your method, but without the rear spring installed how do you accurately measure the final correct position of the back of the T-Arm which will effect toe?

[Michael W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

The presumption is that the frame is positioned at normal ride height.

[Louis C.]

Re: Rear Toe-in alignment with the body off the frame HELP!

For Argument sake I should see a total of one eighth of an inch difference measuring the OD of the back to the front of the tire when done correctly?