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New modified cut/welded tranny X-member brace

Posted By: hemienvy

New modified cut/welded tranny X-member brace - 12/16/23 12:59 AM

I've seen pictures where guys have cut out the crossmember arch that goes over and across the tranny,
then they tied the two cut "ends" together with a reinforced straight piece, under the tranny.

Does anyone make a bolt-on piece that does this ? I'm talking B and E body. A-body I don't know.

You would need to do this if your putting in a physically bigger tranny and need to cut out the tranny tunnel.
Posted By: jcc

Re: New modified cut/welded tranny X-member brace - 12/16/23 04:07 AM

Understand the forces induced here if OEM TB's are still in play, plus the weight the trans mount carries.
If it is a converted coil IFS, the forces are much reduced on this crossmember.
Crash worthiness is another discussion, a cage with a dash bar kinda also needs a lower member to keep the cage in place in that area.
Posted By: AndyF

Re: New modified cut/welded tranny X-member brace - 12/16/23 04:48 AM

Yeah I did that about 30 years ago on my Coronet when I switched over to a Doug Nash 5 speed. It has worked okay over the years. I have a picture of the crossmember that I built back then. I've replaced it with a better design but I don't think I have a picture of the new design.

Attached picture DSC_3232 (Large).JPG
Posted By: Jeremiah

Re: New modified cut/welded tranny X-member brace - 12/16/23 05:41 PM

I cut the floor brace out as needed and on the passenger side splice in a 180°bend of 1-5/8 or 1-3/4 tubing to the oem bracing. On the driver side you can land the tubing perpendicular to the boxed section of the brace. I holesaw through the bottom for weld access.
Posted By: hemienvy

Re: New modified cut/welded tranny X-member brace - 12/16/23 06:57 PM

Thanks guys, I could probably practice my butchering techniques,
but I could have sworn I saw somebody that made one.
Can't remember what I put in the search engine.
Posted By: topside

Re: New modified cut/welded tranny X-member brace - 12/16/23 07:31 PM

I would think that someone could map out the floor contour.
Then fab tooling (maybe using CAD or whatever) to make a shallower but thicker replacement piece.
Or maybe make a 1/4" plate, formed to match the floor contour, for welding in.
There would seem to be a market for such a thing.
Posted By: fourgearsavoy

Re: New modified cut/welded tranny X-member brace - 12/17/23 08:46 PM

Originally Posted by hemienvy
Thanks guys, I could probably practice my butchering techniques,
but I could have sworn I saw somebody that made one.
Can't remember what I put in the search engine.


BigDad made a really nice crossmember for his silver 64 Plymouth with pics posted many years ago.

Gus beer
Posted By: AndyF

Re: New modified cut/welded tranny X-member brace - 12/17/23 09:38 PM

US Car Tool sells a variety of Mopar transmembers for different swaps and such.
https://store.uscartool.com/
Posted By: hemienvy

Re: New modified cut/welded tranny X-member brace - 12/18/23 12:29 AM

Thanks Andy, I guess those will all work with the OE top connector hoop cut out.
Possibly I'm trying to remember something that I never actually saw.

If I used one of those crossmembers, I would increase the size of the bolts holding it in.
The forces from the T-bars cannot be allowed to flex the floor area.
Posted By: mrob

Re: New modified cut/welded tranny X-member brace - 12/18/23 02:56 PM

Here's an option for a 66-70 B-body. It looks beefy enough to withstand the forces of the torsion bar suspension.

Hope this helps.

https://www.holley.com/products/engine_swap_parts/mounts_and_crossmembers/crossmembers/parts/BHS539
Posted By: topside

Re: New modified cut/welded tranny X-member brace - 12/18/23 03:59 PM

That Holley design looks a lot like what I was thinking, but it seems to capture the trans crossmember.
Not the end of the world, though, I suppose.
But I'd prefer a welded upper arch; maybe a short sleeve at each side for the T-bar member.
Posted By: hemienvy

Re: New modified cut/welded tranny X-member brace - 12/18/23 05:02 PM

That Holley thing looks interesting.
Posted By: jcc

Re: New modified cut/welded tranny X-member brace - 12/18/23 07:45 PM

1/2" steel strap? eek
Posted By: jbc426

Re: New modified cut/welded tranny X-member brace - 12/19/23 08:58 PM

Originally Posted by topside
I would think that someone could map out the floor contour.
Then fab tooling (maybe using CAD or whatever) to make a shallower but thicker replacement piece.
Or maybe make a 1/4" plate, formed to match the floor contour, for welding in.
There would seem to be a market for such a thing.


I used a 1/4" steel plate about 4 inches wide and just over 2 feet long welded through the floor pan to the top on the remaining cross member. I had to heat the steel band red hot to bend it and spent time getting it to match the original floor's contour.

I also welded most of the original torsion cross member solidly to the floor pan when I installed the full US Cartool Chassis Stiffening kit. I cut the actual tunnel portion of the cross member down flush, but left the factory flanges and boxed the bottom of the trimmed crossover back in with like-sized steel. I did this fab work with the torsion bars out.

In my case, this was done to fit an overdrive automatic. I may soon be doing further modification, as I'm putting in an even larger automatic to accommodate a more powerful engine.

These are the only pictures that I currently have of the lower modified crossover. I was able to retain the factory cross member bolt locations.

Attached picture 200R4 4.jpg
Attached picture 200R4 5.jpg
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