V-Twin

The frame is identical to the earlier frame apart from the omission of the crossmember and the addition of the batwing bracket. Te frame flexes like mad in the rear without the batwing and even with the batwing it's nowhere near as sturdy as the earlier solution. The suspension pickup points however are all forward of the batwing and as such with the later low performance engines the difference would have most likely been negligible.

turtlevette

His rollbar provides more structural rigidity than that crosmember. There won't be much if any loss of rigidity taking that heavy crosmember out.

The point where things are going to flex are at the kickup point. That's the weak link. That's why i installed a rollbar that attaches the main hoop to the lower frame providing some structural link between the lower frame and the rear of the frame well past the kickup point.

RippoDippo

Eh turtlevette can ya still get the rear window out!

turtlevette

non removable one. It was tricky getting it back in after the welding.

Bee Jay

That is what I suspected. The batwing serves as a better stressed crossmember than the old crossmember (even with strengthening discs), and so GM eliminated the now redundant crossmember. After all of this, I think I will just leave it in for now. Replacing it with a smaller tube will not save that much weight. The only significant weight savings will come from removing it entirely. Maybe after I finish this project, I'll remove it. But for now it will just stay in. I will regret this I know, because it would be really easy to remove now with all of the rear end and suspension out of the car.
Bee Jay

birdsmith

I knew if enough of us piled on we could eventually bash you into submission!!

Bee Jay

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I took it out! I was trying to measure accurately to help make templates for the batwing mounts, and the crossmember was all in the way. I couldn't help thinking how much it would be in the way when it was time for welding. I had some spare time this morning, and using a air chissel and sawsall, I took this useless crossmember out. The weight of the crossmember and the corner brackets that the old differential crossmember mounted to came to a grand total of................drum roll here................

20lbs.

So if I save 15lbs going to the aluminum batwing, and 20 lbs removing this crossmember, I should realize a total savings of 35lbs. Someone check my math. I'll take that, plus my rear end will be 3/4" higher. I'll post when I'm all done.
Bee Jay

birdsmith

35 lbs., eh? That would have been about 35,000 cheeseburgers ago for me!!

Bee Jay

I just re-read my "Corvette From the Inside" book by Dave Mclellan. In 1981, they not only eliminated this cross member that supported the pre-80 differential carrier, but they also eliminated the crossmember that supports the trans tailshaft and gives the dual exhaust a place to go as a chassis structure. I guess what they replaced it with is there just to hold the tranny up, and not as a stuctural part of the frame. My car is an auto, so I replaced the bolt in crossmember with a B&O aftermarket bolt in tubular crossmember. I guess when they designed the C2-C3 frame back in '62, they didn't have computers to simulate and test the chassis. I guess GM was really hot to lose weight back then, and they were really excited about the fiberglass leaf spring. I bought the book back in 2002 at the Monterey Historics when the Corvette was the featured mark. I even had Dave Mclellan sign it, and there is a picture of me and my wife and Dave folded and inserted where he signed the book. I had forgotten all about that. Great book and a good read for us Vette freaks. Like Spock always said, "facinating".

Bee Jay