Factory trailing arm shimming

[Graeme B.]

I'm wondering how the factory set up the trailing arms alignment without the weight of the body on.
Did they have special measurements for this?
Thanks for any thoughts, Graeme.

[John H.]

Re: Factory trailing arm shimming

I'm wondering how the factory set up the trailing arms alignment without the weight of the body on.
Did they have special measurements for this?
Thanks for any thoughts, Graeme.

Graeme -

The rear alignment was done with the frame upside-down, clamped in a precision fixture, with the rear suspension located at design ride height (the rear spring ends were connected later). A sensing head slid inboard against the rear hub, and a central locator pin engaged the machined center of the hub. Two pairs of plungers with linear transducers measured the camber and toe-in angularity of the hub surface, and showed green lights on the operator's panel when the toe-in shim packs were correct, and when the cam bolts on the camber strut rods were set correctly. When the panel was green, the attachments were torqued and the frame moved to the next station. See photo below.

[Graeme B.]

Re: Factory trailing arm shimming

John,that was way beyond the answer I expected.You do know your stuff! How are we poor souls supposed to set alignment on a body off?
Toe-in, toe-out,straight ahead?
Cheers, Graeme.

[Jack H.]

Re: Factory trailing arm shimming

Now you know about the factory's 'Geo' machine! It's why there are no pix of BANKS of Bear alignment machines in the various St. Louis factory photos. Almost all of the suspension alignment was done by simulation...

How do you duplicate? Well, you don't...

Build the car up FULLY and 'grossly' align things by eyeball and/or string + inclinometer. Then, take the car to a professional alignment shop.

[Duke W.]

Re: Factory trailing arm shimming

John,that was way beyond the answer I expected.You do know your stuff! How are we poor souls supposed to set alignment on a body off?
Toe-in, toe-out,straight ahead?
Cheers, Graeme.

It's pretty easy with the body off.

1. With the frame on jackstands on a level surface and the spring not connected, block up the rear suspension to the ride height measurement specified in the AIM and CSM.

2. Measure and mark the true centerline of the frame.

3. Run a string along this centerline with bobs installed so the string is as high as possible to measure toe without interference from any chassis/suspension components.

4. Shim as required to achieve 1/32" toe-in for each rear wheel measured from the string to the center of the tire.

Set the camber before toe. Recheck/adjust camber as necessary after toe is set, then do a final toe check. This method can also be used with the car on a drive-on hoist, but it's a lot easier to do with the body off.

Duke

[Terry M.]

Re: Factory trailing arm shimming

Now you know about the factory's 'Geo' machine! It's why there are no pix of BANKS of Bear alignment machines in the various St. Louis factory photos. Almost all of the suspension alignment was done by simulation...

[John H.]

Re: Factory trailing arm shimming

Terry -

In the 60's, St. Louis had one "Visualiner" alignment rack in Final Process; it was used as part of the daily random audit process, and was also used to re-align cars that had undergone suspension repairs. "Visualiners" were the Chevrolet assembly plant standard in those days.

[Terry M.]

Re: Factory trailing arm shimming

Terry -

In the 60's, St. Louis had one "Visualiner" alignment rack in Final Process; it was used as part of the daily random audit process, and was also used to re-align cars that had undergone suspension repairs. "Visualiners" were the Chevrolet assembly plant standard in those days.

Boy there is a "blast from the past." State of the art in those days was light beams and mirrors. In the field that lasted into the early 1980s as I recall. I know it dates me, but I learned alignment on one of those (light and mirror) machines, but a different brand.

[Graeme B.]

Re: Factory trailing arm shimming

Thanks Duke, that's the way I'll do it .
Cheers, Graeme.

[Wayne W.]

Re: Factory trailing arm shimming

Terry -

In the 60's, St. Louis had one "Visualiner" alignment rack in Final Process; it was used as part of the daily random audit process, and was also used to re-align cars that had undergone suspension repairs. "Visualiners" were the Chevrolet assembly plant standard in those days.

Still is the standard for me. That's what I have in the shop. You wouldnt believe the cars brought in from the fancy stores that pull one way or the other, and the old lite-align gets um straight.

[Steve L.]

Re: Factory trailing arm shimming

This is also they way I'm doing it while the body is off. But I've added two 2x6 x 8ft pieces of wood that run laterally to the frame that I've used to transfer the centerline fishline to 2 other fishlines that run parallel and exactly 3 ft away from the centerline. These wood pieces are butted up and marked to the frame rails so that I can later reset them with the body on and still have a reference to the centerline without having to depend on anything else.

The question I have is when setting the rear camber with the body off, will the camber be changed once all the body weight is back?

[Duke W.]

Re: Factory trailing arm shimming

If you set camber and toe with the suspension blocked up to normal ride height, they should be very close to your settings when the restoration is finished and the car is on the ground at normal ride height.

I hope you are using the OE rear spring as some aftermarket springs don't comply with OE ride height.

Of course, once the car is completed and on the road it would be a good idea to have the alignment checked on a modern four wheel alignment machine.

Duke

[Steve L.]

Re: Factory trailing arm shimming

Thanks Duke,
I mixed original and repo spring leaves so hopefully the ride height will be somewhere near where it should be.

I'll take it in for a real alignment when I'm done.

But I find trying to measure 1/32" toe-in at the tread, not that easy. I had to be absolutely meticulous in every measurement. It took me an entire wknd.

I used the 1 inch holes on #1 and #4 x members as the centerline. I zerod out the camber, leveled off the halfshafts and loaded up the half shafts to take out the approx 0.020" yoke play and measured from the top of each disk to centerline and found that the running gear was off laterally until I loosened the diff mounting bolts and moved the diff to the other side of the bolt to hole clearance. It looks like the real centerline at the back is the between the yokes centerline of the diff rather than any frame reference.

This was an interesting excersise but I'm glad it's over.

[Duke W.]

Re: Factory trailing arm shimming

Setting alignment is a precision task, which takes care and patience.

Professional alignment equipment is very accurate, but the trouble is finding a guy who understands how to use the equipment, understands alignment, and is willing to set it to my specs within my specified tolerance.

I gave up 25 years ago and do all my own alignment with an inclinometer, tape measure, and string, and I get it "my way", but it does take a lot of time.

I've only had one of my cars I on an aligment rack since then, and it was well within acceptable tolerance for the settings I dialed in.

Duke

[Steve L.]

Re: Factory trailing arm shimming

Duke,
Do you know what the professional alignment equipment use as a reference to determine the car centerline?

I'am guessing that it is the wheel hubs front and back.