KLUTZ

First question.. Are all C3 frames supposed to measure up exactly like they are supposed to in this diagram?



I'm having an issue right now regarding the body mount brackets. I measured, marked, measured, marked and scribed again the EXACT location of the passenger side bracket. I cut the old one off and tack welded first to make sure all lined up correctly and when I was assured it was the exact spot of the old one, I finished the welding job.



So on to the driver side. Well the entire section where the bracket was was rotted out so I had removed and replaced that section. For this reason I had on previous position to go by. So I went by the diagram up top, did my measurements, (I also measured from the two small indents at the side of the brackets) and tacked the bracket on the exact spot I want it.



So.. I get my measuring set up again and the one I just tacked on is exactly 17 1/8" from the 3/4" gauge hole to the centre of the bracket hole. Just as the diagram shows on the driver side. But.. I then go and measure the passenger side bracket and it is 17 5/8" from the gauge hole. That's a half inch further to the back of the frame. I don't see a measurement for the passenger side but one would assume they would be in the exact spot wouldn't one??? As I said though, I put the bracket in the exact same spot as the one I took off.

Here is how it's looking though. Still have to repair the box section and rear frame on the driver side but I really hope I don't have to remove the bracket I have fully welded on... Is it possible both sides aren't the same? Thanks for any advice or opinions...

Tbone39772

I checked my 77-78 frame manual and you are correct in the 17 1/8 from the 3/4 gauge hole (centered). Make sure that you are measuring correctly from station to station, not point to point. Also would suggest that you measure from the most aft body point and go forward to gauge hole and then subtract the 17 1/8. A half inch deviation is not too bad for a frame because you can shift some for alignment. Your frame is wide open at this point so you should be able to find problem easily (hope the frame isn't tweaked). Hope this helps. Also remember your datum line. Use that for all measurements.

KLUTZ

Thanks.
When I'm off later this week I think I'll flip the frame upright and try to do some more measuring that way. I'll get a couple helpers on the other end of the tape as well. I'm hoping it isn't "tweaked" either. If I don't figure it out I do have a friend with a rack who could check it for trueness (is that a word?)

CTVETTE78

I did exactly what you have done here on my 78 when I restored the frame; I was very careful to re-weld the #1 body mount using the same diagram you show above. All of my measurements were right on. When I dropped the body back on, that #1 mount was ½” off of where the mounting hole on the rocker channel wanted it to be. The other 7 mounting points were spot on, and I had steel rods on the jig holes along the rocker channels on both sides.

I ended up cutting the mount back off and re-welding it where it needed to be.

Tbone39772

That is interesting but not uncommon. Most, and I do mean most, full frames have some deviations from specs. (factory) Especially in the earlier years. It may be possible to measure the body and get those dimensions from that. It would clarify a correct dimension. My 78 manual (same vendor as yours) has the fwd width a little different but everything else the same. To check the tweaked dimensions just X out the diagonals and divide by 2. That would give you the frame (ladder type) from being out of square, which I doubt if your other measurements check out. Good luck!!

Procrastination Racing

A Corvette frame has five mounting points on each side.
1. Radiator
2. Front cowl
3. Door sill
4. Trailing arm pocket
5. Real luggage bulkhead

#3 is used on 1963 coupes and all convertibles only. As such, your 1979 has mounts 1, 2, 4, and 5.

Cross measure and check the same from each side.

For example, 2Driver to 4Passenger should equal 2P to 4D. Also check 4D to 5P and 4P to 5D. Check each set that way to see if the frame is tweaked.

With it bare, it is easy to get to a frame shop, although rolling makes it easier.

It is a good idea to bolt a block to the motor mounts and set a bellhousing and transmission in to ensure that the mounts stay true if they do straighten it.


Just thought, 1979 frames were thinner, and easier to twist, as they were into saving weight for economy then, and there was no need for heavier frames (no big blocks). It is very possible to have the frame twisted slightly.