Racers, chassis experts, is this frame crossmember needed anymore?

Yellow73SB said:

My new harness mount is lower than the seat holes

I'll take some pics

Click to expand...

20 degrees downward is acceptable according to GCR.

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

What do you mean? The ony change is that they went from a dual opening crossmember to one that has a kickup on the passenger side for 1 pipe to pass under, since the cars used a 2-1-2 cat system them. The beam is still a bolt in to the frame, just like all the ealier years 9except early manual weld in ones) and as such provides the same function as the earlier ones.

This is what the later crossmember looks like (although it's a little modified on the dr. side so the other pipe can pass under there).



Where is the weight savings? How is this not a structural member like the other one? The crossmembers are a tight fit in the U shaped frame brackets where the through bolt passes through and the 2 bolts that go up into the frame are identical.

Twin_Turbo said:

What do you mean? The ony change is that they went from a dual opening crossmember to one that has a kickup on the passenger side for 1 pipe to pass under, since the cars used a 2-1-2 cat system them. The beam is still a bolt in to the frame, just like all the ealier years 9except early manual weld in ones) and as such provides the same function as the earlier ones.

This is what the later crossmember looks like (although it's a little modified on the dr. side so the other pipe can pass under there).



Where is the weight savings? How is this not a structural member like the other one? The crossmembers are a tight fit in the U shaped frame brackets where the through bolt passes through and the 2 bolts that go up into the frame are identical.

Click to expand...

Looks like you are right TT. I wonder if he was refering to the 4spd crossmember. Didn't the four speed disappear somewhere in that time frame? Is the bolt in just as structurally strong as the weld in?
Bee Jay

No, the weld in will be stronger but yours wasn't welded in originally either. I think that was only the case on the frames that still used the aluminum body mounts (up to 72???)

Twin Turbo was right, and I was wrong. The only crossmember deleted with the addition of the aluminum rear end is the crossmember that had supported the rear end. The tranny support cross member was deleted for the C4. But now I am wondering how they hold the tranny up. The rear mounted tranny and torque tube didn't come out untill the C5 right? I wish this book had more pictures and drawings. After all, we are knuckle dragging Corvette owners, right?
Bee Jay

The C4 has a large c beam that connects the trans to the diff. It's sort of a backbone but them not tying into the frame makes the C4 notoriously weak and flexy:

You can see it here

Yellow73SB said:

My new harness mount is lower than the seat holes

I'll take some pics

Click to expand...

I just checked again and it's not

I don't why I thought it was lower, I knew I didn't put it lower

It does look like it's lower at first glance though