TXjeepTJ

iTrader: (8)

I fabbed up a transmission crossmember using the stock crossmember mounting holes.

After completing the crossmember, I lowered the jack from holding up the transmission and the transmission sagged about 1/2". I am also able to easily bounce the transmission up and down.

All of this play is coming from the frame rail mounting points - as I can see the bottom of the frame twisting whenever I move the transmission up and down.

I used the stock crossmember to frame mounts (cut them off and welded them to my new crossmember) so it had to have been doing this with the stock crossmember.

Anyone have any ideas? Is this normal?

Toddoky

Can you post up some pics?

1964SS

iTrader: (1)

Pics would greatly help. It sounds like the crossmember itself is not stiff enough causing the frame rails to pull when it flexes.

TXjeepTJ

iTrader: (8)

Thanks guys, I'll have to get pictures when I get off of work.

I used 1/8" thick 1.5" square tubing, welded all over. Seems pretty stiff, but that could be the issue. Wondering if I should just order a G-force crossmember

toytech93

iTrader: (2)

This must be a hardtop with open frame rails. I highly recommend boxing the frame closed especially with any real horsepower. A couple company are making boxing kit now, hellwig and HPI customs. I used a HPI kit, its a great kit but I don't think you can install theirs with the body on.

http://www.hellwigproducts.com/produ...fx-by-hellwig/

TXjeepTJ

iTrader: (8)

Correct, hardtop w/ open frame rails. I was wondering if someone was going to chime in and mention the frame might need to be boxed. I definitely do not want to cover up a major problem though (weak crossmember)

This car has a 6 point roll cage installed by the previous owner who was running it w/ a 650rwhp big block - I'm guessing he didn't box the frame as the roll cage did the job of stiffening. He did run the big block setup with the same crossmember mounting points, I just don't know if it was bending the frame rails or not like I am seeing

chuckd71

iTrader: (23)

If the crossmember is strong enough to flex the frame as it is, what would a stronger crossmember do to fix that? It seems you have identified the weak frame as the source of the troubles, so offhand that would appear to be the place to start, otherwise you're just building a castle on a foundation of sand. But I dunno. Just a thought.

MorePSI

Frame flex is not a sign of a weak crossmember but instead a frame lacking rigidity. A roll cage does not make the open channel rail more torsionally rigid which sounds like the issue you have. The crossmember is applying a moment around the weakest axis of the c-channel , box the rail and the frame is much stiffer.This is a blind, semi-educated guess without any pictures to go off of though for if you have other factors at play.

Edit: .125" wall 1 1/2" steel box tube is plenty strong for a transmission crossmember if the joints were properly angled and welded. It should not sag anywhere close to a noticable amount.

Cyrus Johnson

My first homemade crossmember was as bad or worse at flexing. Got the crossmember kit from Art Morrision and that fixed the problem. However if a crossmember was available for my car at the time, it would have been much faster and easier to just buy one.

TXjeepTJ

iTrader: (8)

I ordered an aftermarket crossmember that was supposed to get in today, but of course anytime I order something there is a snow storm going on..

To be honest, I really don't want to run the crossmember I made anyways. Ugly welds (but solid welds) - so I figure I would just buy one now and mark that off if it doesn't fix the problem.

Project GatTagO

iTrader: (7)

These cars weren't exactly rock solid, even when they were new. Add to that 45 years of use, abuse, and neglect, and it only gets worse. Honestly, I wouldn't worry about 1/2" of sag, whether it be at the crossmember or at the rails. I don't notice any sag on mine, but then again I have a relatively light trans (90 pounds), and it's shorter then a T56 or an automatic. All those things play a factor.

Andrew

Bowtie316

iTrader: (1)

If a crossmember triangulated the top of the frame rail, the bottom of the frame rail to the transmission mount, and was rigid across it would be pretty strong.