Checking a Frame

[Patrick B.]

I am measuring a friend's 65 frame to determine the right number of shims for the various body mounts. My first step was to try to level what I think are the primary gaging points. I have drawn arrows on the attached frame drawing from the chassis manual to show what I mean. I have leveled the frame laterally so that the two holes in the frame below the motor mounts (the 16" dimension in the drawing) are level. My next step was to level the frame longitudinally so that the rear gaging holes (which are the trailing are attachment holes) were 1" below the forward gaging holes.

The problem is that the trailing arm attachment holes are not level. One is about 1/4" below the other. Is this within the ordinary tolerances of the frame? When I measured my own 67 frame years ago I thought that all four gaging holes were very close to level. Hopefully this amount of frame twist is inconsequential, and I am hoping to get some informed opinions on the matter.

[Gene M.]

Re: Checking a Frame

Pat
I would be more concerned if the 70 1/8" dimension were out.

Determining the shimming will be determined when you put the body back on the frame and attempt to set door gaps. It is always a try and see type of assembly. Start with what the shimming was when the frame was removed.

[Patrick B.]

Re: Checking a Frame

Thanks Gene ---- We will check the 70 1/2 dimension. I'm glad the 1/4" warp does not strike you as too bad in itself. In this case, the original shims were pretty degraded and just a mess on the floor after the body lift. We are going to replace one door and part of the rear door jam panel and we need a place to start when we place the body on the frame temporarily.

I believe the body was bonded together on a jig that followed the dimensions of the frame as represented in the drawing. However, the elements of the frame tend to distort with the heat of the welding process and the shims are required to restore the relative positions of the body mounts. I think an accurate measurement of the body mount heights with a surveying transit or laser device can predict the correct shim configurations to at least a very good starting position for fine tuning by a skilled body shop.

I had an opportunity to test this theory last week. A very perfectionistic restoration shop did a beautiful job making the body of my 67 convertible much better than original with perfect gaps and fits of the doors, hood ect and a great paint job. When I brought the chassis to the shop last week, I told them I had measurements of my frame to compare to the frame drawing to guide the shiming. As you would expect, they said they did not care about the measurements or the what the factory shim counts were. They would determine by trial fitting the body what shims were required to maintain the excellent panel fit they had achieved with the body on their body buck. They asked did I want them to do it my way or their way? Not being a complete fool, I certainly agreed that they should do it their way. But, I said I wanted to mark 2 body mounts where the measurements predicted they would subtract shims and 2 body mounts where the measurements predicted they would add shims. They performed the body drop expertly while I tried to stay out of the way. In the end, they had removed the shims from the mounts I measured as high and added several shims to the mounts I had marked as low. I do believe the measurements are at least as accurate as counting the factory shims which is not always possible.

[Timothy B.]

Re: Checking a Frame

Pat,

IMO, bottom line is you want to body to sit on the frame like it sat on the body truck when it was assembled. The four cage mounts (firewall and in front of rear tire are supposed to be on the same plane so put three or four shims on each of them and sit the body down.

Make sure the suspension is normalized, fill the gaps in the rearmost mount (behind tires) with shims then with the car on a fairly level floor stand back 20' +- and look at the rear. If the body is not flat (left to right) put shims in the rear mounts to make it flat and make it high enough above the #4 frame cross member. If it's a coupe these rear shims will require you to check the shim count on the mount in front of the rear tire because the coupe body is rigid and it may lift some, if it's a convertible I don't think it will change much.

You then need to hang the doors for best fit and work on getting a straight style line front to rear. You can add/remove shims to achieve this style line.

[Gene M.]

Re: Checking a Frame

Pat
Keep in mind the body fixture used to do the body and set gaps is most likely slightly different dimensionally from from your cars frame. And typically the shimming is not the same yield as the original in order to maintain those gaps. So original shim counts typically do not yield the best body fit.

[Patrick B.]

Re: Checking a Frame

Gene -- the 70 7/8" measurements you suggested were both right on, and the diagonal measurements we made convinced us that the frame was not parellelogramed. The height variations between the frame and the drawing were fairly small and random so the warp at the rear trailing arm holes is probably within normal tolerance. Although the body had damage front and rear, the frame appears to be ok.