Frame Shims

[Michael H.]

Ever wonder how the frame shim count was determined in production? There were actually two different methods used from 63 to 81 at the St. Louis plant. The first system, in the 60's, measured the frames body mount pads at the first station while the frame was still inverted and before anything was attached. Later, this system was moved to a point further down the chassis line, just prior to body drop. The following pictures are of the later system.

Michael

[Michael H.]

Frame Shim Checking Fixture

Fixture being lowered into frame.

[Michael H.]

Fixture In Position *NM*

[Michael H.]

Frame Shim Tool

This tool was slid into the frame/body mount gap which automatically measured for the correct number of shims. The entire operation took just about two minutes.

[Terry F.]

Re: Frame Shim Tool

So, basicly they are assuming the body is true and the frame is slightly irregular. I think a person could level there bear frame on a solid floor and then use a laser level to find the lowest points. You could look at the assembly manual for the height of each mount. Actually, the laser could shoot level under the frame and then you could take a tape measure and let the laser hit it under each mount location. A little math and you could figure how many shims should go in each location. Trouble is that many bodies settle to the frames they are originally on.

A person might do better putting the body on the frame and measuring wheel clearances, etc. Just a thought, Terry

[Michael H.]

Re: Frame Shim Tool

Yes, that's exactly right Terry. Bodies are built to zero, or design specs, and must be assembled to a fixture (the frame) which is also at design spec. As John Hinckley explained in an earlier post, the frames are never at this exact dimension so they must be shimmed to come up to design spec. The body is much more flexible than the frame so even if the body warps slightly after being assembled, it will pull back down to the correct dimensions when bolted to the frame.

I suppose there are several different ways of selecting shims for a chassis when the originals have been lost and I suspect the laser method would be the most accurate but I have no experience with this so I leave that to those who have.

[Terry F.]

Re: Frame Shim Tool

I have never delt with it either. But I always wondered which was being shimed to....the frame to the body or the body to the frame. Thanks for the pictures. That machine is crazy looking and heavy looking. Looks like they sat it in place and stuck the tool in to measure the gap. I could use a job like that guys in the picture. Terry

[Bill W.]

Re: Frame Shim Tool

We had a few of the old St Louis plant assembly line workers at our Corvette club meetings. They told us they only gauged 1 or 2 out of every 10 frames.

[Tom R.]

Shim Indicator

Engineer at the plant I've gotten to know called this the shim indicator, describing this as wedge shaped.

[Tom R.]

Shim Predictor

Same engineer called this this geometrical fixture a shim predictor...these are plant names for these tools.

[John L.]

Re: "2" in the picture

Anybody know what the 2 was for just infront of the rear kickup in the second picture ???

[Michael H.]

Shim Pattern Chart

Bill,

The only shim count that I can think of from that area that was random checked was the front end alignment shims at the upper control arms. There was a chart on the wall that listed the current shim count for all four locations and this setting was checked about one out of ten or twenty jobs. (I still have a few of these charts) I would have to guess that this was what the workers were describing to you instead of the frame shim check. I've watched, for hours, one frame after another come through and the shim check process was done to each and every one.

In the 60's (and possibly early 70's) this was one of the very first things that was done as the frame was placed on the frame buck at the beginning of the chassis line. It was upside down on the buck and no additional fixture was required so there would be no reason to skip the shim check process.

There would be no logical reason why 80% of the frames were not checked. It was a critical part of the build and adding a random number of shims could be disaster on some bodies. Checking shim stack dim on every tenth frame wouldn't even have been a time saving step as the frame had to be on that buck anyway and the entire check procedure only took about thirty seconds.

Michael

[John H.]

Re: Shim Predictor

That's what it said on the Tool Drawing, but the guys on the line called it "The Spider"

[Michael H.]

Re: "2" in the picture

John,

The "2" in the pic was the shim count. If you look at the 1st pic you will see that the "2" isn't there but after the fixture was in place in the 2nd pic, the "2" had been written.

The hash marks used for shim count in the 60's and 70's were eventually replaced with the actual number of shims required.

Michael

[Kevin M.]

Re: Frame Shim Checking Fixture

What model or year car is in the pictures? It has blue paint?

Kevin