Body shimming poser

[Chuck R.]

In the near future, I'm going to be dropping my Colorado purchased late production 68 body onto my California purchased eary production frame.

As the frame had next to no rust, all shim marks were visable. Can I refer to these shim marks when I mate these two mongrels together, or should I discount them all together?

Just seeing if I can save some time in the trial and error department.

As always, thanks

Chuck 32205

[Chuck S.]

Re: Body shimming poser

Chuck, from my time here sitting at the feet of the old masters, I understand that the frames are where the distortion occurred; the bodies were built to perfection on a jig. I would start with EXACTLY what the marks on the frame say, and then check the body gaps; I bet you will be dead on the first try.

[Wayne W.]

Re: Body shimming poser

I wouldnt count on it.

[Chuck S.]

Re: Body shimming poser

Wayne, since the frame and the body are the same model year, it would seem to be a very good starting place, if not dead on.

If I remember correctly, it was said that the frames were "gaged" with a fixture and "shim-marked" for a "datum", not for any particular body. The frames never saw any particular body until body drop. THEN, as I understand it, there may have been some fine tuning of the shims at body drop depending on how carefully the gaging was done and how true the body was fabricated.

The frequency of these body drop shim corrections would be demonstrated by how often the shim counts don't match the marks; anecdotal reports seem to show that it happened, but not frequently.

[Chuck R.]

Re: That's my take as well Chuck

but I guess I needed to hear it from another with more active nurons than me.

When the time comes, I'll let you know if the original marks were true to form.

Thanks for the responses Gents,

Chuck

[Chuck S.]

P.S. Wayne's Been Doing This Awhile...

Chuck, so he probably knows how things work out in real life.

You can check out the archive below for interesting reading...however, if I was arbitrarily picking a number of shims to try, I would start by picking the marks on your frame.




NCRS Archive November 8, 2002

[Duke W.]

Re: P.S. Wayne's Been Doing This Awhile...

If John H sees this he can weigh in, but I recall he posted some detailed information on this issue. The sill member - bottom U-channel of the birdcage - was considered "flat" and a gage was used on the frame to measure the space between the top of the body mount brackets and gage, and from this the chalk marks were made on the frame to indicate the number of required shims at each bracket. The shims were added further down the line just prior to body drop and "secured" with a loop of masking tape to keep them in place during the body drop operation and torqueing of the body mount fasteners.

Duke

[John H.]

Re: P.S. Wayne's Been Doing This Awhile...

During the original build, the mounting points on the body were controlled to design "net" by the build truck pedestals, and the variable was the frame, whose mounting points were shimmed to match the design datums for the body. After many years on the road, however, it's likely that the body has deflected to whatever extent the frame, mount brackets, and mounting cushions have deteriorated. The markings on the used frame would probably be a better starting point than no reference at all, but I'd expect to make some trial-and-error shim adjustments to get correct gaps and door fits.

[Bill W.]

Re: P.S. Wayne's Been Doing This Awhile...

I would start with about 3or 4 shims on each mount. torque birdcage mounts to correct specks check gaps adjust as needed. if its a conv.expect alot of adjusting . those factory marks dont mean much 35 years and 2 bodys later.you gotta ask yourself if that new frame is so good why dont it have a body? I would do some measuring on the "new" frame before the drop just to be sure. Bill. ps make sure the body is sitting on all 4 wheels before making adjustments.

[Wayne W.]

Re: P.S. Wayne's Been Doing This Awhile...

Exactly, And thats why I say don`t count on it. Thirty five years of who knows what kind of stresses and a 68 to boot. Start there if you want, but dont be surprised at what you find.

[Chuck R.]

Re: Great feed back!

I'll start off with the original shim markings and go from there.

I would have never taken into account the body/frame deflection factors, but it makes sense, My frame seems to look a little more deflected every morning I strike my Arnold pose in the mirror.

Thanks folks,

Chuck

[Chuck R.]

Re: Shim marks

On the #3 driver's side mount, I am having a hard time figuring out if it's a zero or a really fat six.

The passenger's side #3 mount is definately a circle/zero.

Were all shim marks along the lines of roman numerals (straight lines) with circle marks meaning zero?

Just curious as I'm sure I'll find out at body drop.

Thanks,

Chuck

[Chuck S.]

Re: Shim marks

Chuck, it sounds like 68 must have used the 67 (and earlier) "slash" line style marks. Unless there are other clearly discernable Roman numerals like "IV" or "VII" on the frame, I would assume these are actually not Roman numerals but a slash mark for each shim; e.g four in Roman numerals is "IV", but in pre-69 Corvette shim marks (I'm assuming), four shims would be indicated by "////".

Shim marks on 69 and later cars are in Arabic numerals; i.e. four shims equal "4". Zero shims is the same for both pre 69 and later, therefore a "fat six" cannot be an Arabic six (6) in 68...it really has to be a zero (0) in the pre-69 marking system.

[Chuck R.]

Re: Thanks Chuck, I think So too

It must be a fairly straight frame then as the #2 mounts only require // on each side

Thanks again,

Chuck