Woodie

I'm sure one or more of you guys know.
Why were body shims used?
Was it because the frame were off - twisted from welding or because the bodies were off? Or both?
And how much off could the frames be and still be used?
I'm sure they were not all perfect. Say up to 1/2 inch? Or more?

John McGraw

The shims were used to adjust for the frame twisting and warping during welding. The jig that determined the shim count was lowered over the frame, and then the shims were selected. The same jig was used for all cars, so it could not have adjusted for body problems. The shims were selected and taped in place on the chassis long before the body was lowered on to it. I have seen factory stacks of shims (with the masking tape still in place), that exceeded 1/2".


Regards, John McGraw

JohnZ

Frame fabrication tolerances were +/- 3/8" from nominal datums; the shim packs compensated for those dimensional variations. The body was bolted to a machined steel build truck while it was assembled, and was considered as being "to design".

Harps

John & John, that's great info on this! It's great to hear about the old process on this.

We have two original Survivor cars (a 72 LS5 with 1,700 original miles, and a 67 427/390 car with 30k orig miles). You wouldn't believe how nice the old masking tape is on the 72, its aged in appearance but looks perfect still at each body mount. The 67 has its tape in some places still too, just not as perfect as the 72. It's always great to see original masking tape on a Survivor car.

MasterDave

And here all this time I thought it was due to the variations of fiberglas thickness on the undercarriage. Bodys were set on the frame, leveled, gaps measured and shims taped on. Go figure....

JohnZ

Nope. A master gage fixture measured the gaps from each body mount bracket on the frame to the gage while the frame was upside-down in the first station on the Frame Line, and the operators marked the number of shims required at each mount location on the frame. The chassis arrived at Body Drop about two hours later, and the operators there installed the upper body mount cushions and the corresponding shim pack on each body mount bracket and taped them in place just prior to dropping the body on the frame.

OC-1

original front shim on my 61 with tape

hokie04

I presently have my body off of the frame. So are you saying I can calulate the number of shims I need at each mount before I drop the body? If so is the factory mount heights in the AIM manual or where could I get these measurements? My shims were basically gone when I removed the body so I am just guessing at this point. This sure would be a lot easier than dropping the body on the frame and then trying to fill the gaps with shims.

MasterDave

So you're saying it was all frame? Why the big difference in shim thickness? Were they that bad at holding specific tolererances?

John McGraw

Yep, it was all frame! As John said, the spec. was +- 3/8" at each location. with this type of spec, it is possible to have 3/4" difference between any two mounts. Not very likely, but possible!

Trying to calculate the shim stack from the frame in a current restoration by using the frame only, would take a lot of fancy measuring equipment and a surface table to mount the frame to. High end frame and fabrication shops would have such datum measuring equipment, but not your average restorer. Setting the shims with the body is not that tough to do, and will give better results on a body which has not been bolted to an assembly plate for over 40 years.


Regards, John McGraw

zim64

Ditto John, I rebuilt all the suspension and drivetrain components, then I set my body, then inserted shims to take up the gap, let it set a couple weeks readjusted the shims if needed, and bolted and torqued them in place, all this before doing any body work, as I replaced all 4 wheel openings (flared). I wanted to be sure that the body was settled to the frame before disturbing any panels.

al329

Have yet to put my body back on but I will be using this paper as a guide.

http://www.lbfun.com/warehouse/tech_...0C2%20Body.pdf

Vogie

You might be able to use a water level - a container with small tubes long enough to reach points to be referenced. The water would be at exactly the same height in the container and each of the tubes no matter what position you were measuring and no matter what the condition of the surface on which you were working. Just a thought.