71 Shim Marking Color?

[Sheldon S.]

My car is a 71 with a April 29 Build date, I am trying to figure out what color the shim markings would be. All the markings on the body for the options and job # are in white crayon. There was only one shim marking that was slightly visible and it appeared to be white but it had overspray on it. Would white be correct or should it be green? What was the most likely color for that period?
Thanks
Sheldon

[Bob D.]

Re: 71 Shim Marking Color?

If I recall correctly the body shim markings on a '71 were done in green crayon. The number of shims was written in arabic numerals as opposed to roman numerals seen on earlier Corvettes.

[Michael G.]

Re: 71 Shim Marking Color?

I too have uncovered green crayon on the chassis of my 71.

[Paul O.]

Re: 71 Shim Marking Color?

I would expect to see Green shim marks when judging the Chassis on a 1971 and at least 1 position with zero shims. The reason I say this is when the frame was checked for the number of shims each mount would need. The tooling used would have to make contact at at least 1 mount point and possible more. The line worker would then use a stepped gauge depending on how many steps the tool went in was the amount of shims that position needed. He then would write the number next to the mount position. He could write zero but would expect nothing to be written.

Paul 18046

[John H.]

Re: 71 Shim Marking Color?

The tooling used would have to make contact at at least 1 mount point and possible more.
Paul 18046

Paul -

The frame shim gauge fixture located to the master datum holes in the frame, not to any mount; all of the mounts were subject to the +/- 3/8" location tolerance, so referencing the fixture to any mount would automatically induce initial variation into the shim determination process. This was true of the '63-'68 fixture used with the frame upside-down in the first station on the Frame Line, and with the later C3 overhead-hung "spider" fixture located just prior to Body Drop.

Although you may find one or more mounts indicating zero shims, it would not be correct to assume that every car must have one location marked for zero shims.

The primary gage datum hole is shown on the side view of the frame diagram in Section 2 of the Chassis Service Manual, adjacent to the steering gear mounting holes, and the other two vertical gage datums are called out on the master frame assembly drawing.

[Paul O.]

Re: 71 Shim Marking Color?

John thank you for your insight you are always a great help in understanding the assembly line process. So John you are saying that the fixture was suspended above the frame on 69 and on frames till it hit all the datum points then the line worker used the shim tool to determine the amount of shims needed. On earlier frames the process was similar but the frame was inverted and earlier on the frame line.

Paul 18046

[John H.]

Re: 71 Shim Marking Color?

John thank you for your insight you are always a great help in understanding the assembly line process. So John you are saying that the fixture was suspended above the frame on 69 and on frames till it hit all the datum points then the line worker used the shim tool to determine the amount of shims needed. On earlier frames the process was similar but the frame was inverted and earlier on the frame line.

Paul 18046

Paul -

Yes, that's exactly how it was done. Photo below shows the later "spider" shim determination fixture, courtesy of member Michael Hanson.

[Paul O.]

Re: 71 Shim Marking Color?

Thank you John.

Paul 18046

[Steve L.]

Re: 71 Shim Marking Color?

John,
Any chance of getting a copy of your frame drawing?

Also, where are the other two vertical references- are they at the TA pivot points?

[John H.]

Re: 71 Shim Marking Color?

John,
Any chance of getting a copy of your frame drawing?

Also, where are the other two vertical references- are they at the TA pivot points?

Steve -

I don't have that drawing - I photographed it at Vette Products of Michigan while doing an article on Neal's frame operation. I don't recall the other two datum points - it was a long time ago.

[Chuck S.]

Re: 71 Shim Marking Color?

Thank you John.

Paul 18046

Paul, I thought exactly the same as you did. The interesting thing I learn from John's/Michael's photo is that not only is the frame right side up, but it's virtually a complete rolling chassis without wheels...the drivetrain and suspensions are already installed.

[John H.]

Re: 71 Shim Marking Color?

Paul, I thought exactly the same as you did. The interesting thing I learn from John's/Michael's photo is that not only is the frame right side up, but it's virtually a complete rolling chassis without wheels...the drivetrain and suspensions are already installed.

Chuck -

Engineering changed the shim determination process early in the C3 era from upside-down in a fixture on the Frame Line (C1-C2 process) to right-side-up on a fully-assembled chassis just prior to Body Drop to more accurately reflect the influence of installed component stresses on the frame at the point where the shim gaging was done. The underbody was always considered "zero-datum", as it was bolted down solid to machined pedestals on the steel body build truck in the Body Shop while the body was assembled.

[Chuck S.]

Re: 71 Shim Marking Color?

Chuck -

Engineering changed the shim determination process early in the C3 era from upside-down in a fixture on the Frame Line (C1-C2 process) to right-side-up on a fully-assembled chassis just prior to Body Drop to more accurately reflect the influence of installed component stresses on the frame at the point where the shim gaging was done. The underbody was always considered "zero-datum", as it was bolted down solid to machined pedestals on the steel body build truck in the Body Shop while the body was assembled.

Thanks for the knowledge, John.

I was wondering if the change was made to take chassis loads into account.

[Steve L.]

Re: 71 Shim Marking Color?

John,
The shim fixture must have picked up on the two front alignment holes, one on each side. Where would it pick up on at the back. I would have thought it would have been on the TA pivot holes. But by then, the TA would be in place.

You need at least 3 points to define a plane.

[John H.]

Re: 71 Shim Marking Color?

John,
The shim fixture must have picked up on the two front alignment holes, one on each side. Where would it pick up on at the back. I would have thought it would have been on the TA pivot holes. But by then, the TA would be in place.

You need at least 3 points to define a plane.

Steve -

I don't recall offhand where the vertical datum point at the rear was located; it's on the master frame assembly drawing, but I don't have it.