C3'rs,
Due to problems with my Achilles' Tendon I can no longer operate the manual clutch in my 75 Convertible. Somewhere along the way I acquired a frame from a C3 automatic. Based on pictures from the 1971 corvette registry - specifications I believe it's from a 1978 automatic car.

What modifications must be done either to the 78 frame and/or the 75 body to drop the 75 Convertible on the 1978 automatic frame?

Appreciate any help before I get in too deep.

Thanks
MarkV

 

MarkV, I`m not an expert on frames, but have worked on many. I think you have the option of using the frame you have and swap transmissions, if the original frame is good. I did find an article on frames, I will post it.

 

Thomas77,
Thanks for the reply.
I've been told I can't put an automatic transmission in a manual transmission frame because the crossmembers are different. Don't know if it's true though.
Thanks for the picture. I've seen it. I hope it's correct.
MarkV

 

The difference in the cross members is the auto will unbolt,the stick is welded in. The swap in tranny's should work but it would be easier to install engine and transmission together.

 

74Harley,
Have you installed an automatic in a manual C3 car? The experts at one of the online aftermarket Corvette distributors said it can't be done. I don't recall why other than that's not now the factory built them.
Thanks
MarkV

 

Yes that is true, the automatic cars had boltt in crossmembers, I have a 77 automatic now, it has been awhile since i was under a 4 speed car, Hopefully you will use a 4 speed automatic, you won`t regret it. Shorten the drive shaft a few inches. Swapping the frames would I think would be your best bet,I read the 78 frame is slightly lighter not sure that is true. Back in the late 60`s brother bought a new 68 roadster, 327 4 speed nice car.few years later it became a 427 L88 4 speed, (Very fun street car) then later race track only. We built a trans crossmember for that, for quick trans removal. It was 4" steel channel iron with one bolt on both ends, with side exhaust, It would not allow you to use under car exhaust. Someone built trans crossmembers for 60`s, 70`s cars, not sure I saw one for corvettes, It might have been Summit, not sure. good project car.

 

Thomas77,
Great. The die is cast.
Thanks
MarkV

 

I believe the convertible frame had a few extra gussets welded in for stiffening because of the lack of the T-tops.

 

While I personally have not done it I have seen the results. There's a 68 convertible I am looking at and it was a BB 4sp. car. The last time it was running it had a SB auto.

 

personally its easier to modify the frame you already have and also convert the peddles and install the trans mount for a auto..... than trade the whole frame....