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I’m in the process of converting my 72 Vet’s transmission from the stock 400 to a 700R4. My last task is re-hanging my exhaust.
I’m looking for ideals for supporting the exhaust system in the transmission crossmember area. I changed the crossmember to the G-Force bracket, I have stock exhaust manifolds and I’m attempting to re-use me old exhaust system which is 2 ½” pipes.
Not familiar with the "G-Force bracket", but when I did my 700R4 swap, I found I couldn't get the passenger side exhaust pipe to clear the right side of the transmission, and go through the crossmember smoothly. My solution was to cut the crossmember and remake it with the hole for the exhaust farther to the passenger side of the vehicle. I then used a factory exhaust mount, but modified it by lengthening one side so it would support the pipe in the new location. I then reworked the exhaust pipe to go through the new hole in the crossmember. Probably not the simplest solution, but when it was done it was difficult to tell from stock.
On my Richmond 6 speed there is big lump on the passenger side so I could not use the center exhaust support bracket as orginal. After a bunch of experimenting I turned the end to face forward (instead of aft) and then trimmed, bent, and tweaked the bracket to hold the 2.5" pipes.
I do not have a good picture of the bracket, but you can see the way it holds the pipe here:
I don't think it is necessary. They were never attached to the stock crossmember. And it shouldn't be attached rigidly. And that crossmember looks like it doesn't need the bottom closed off. I saw one stock crossmember with the tops cut off the exhaust loops. Back of tranny isn't that heavy but I feel it is a little weak that way. But being able to drop crossmember while leaving exhaust intact would be nice. Your exhaust clamps. The bolts hanging are creating a low spot. Might wanna turn them so bolts are not hanging down.
Can't tell what kind of room you have above the rubber tranny mount. The original support sits on top of that rubber mount so that it can hold the exhaust pipes without having direct metal to metal ratting. Quite witty really.
From the last picture it looks like you have room to fabricate a mount (or modify the stock one) so that you can clamp the exhaust pipes onto it.
Can you get us a snapshot of the rear tranny mount? To see how much room there is towards the exhaust pipes. It took me a few remove&replace times to tweak my modified and NOW forward-facing tranny mount to support the pipes in the correctly centered place in the crossmember exhaust holes. You should have it a bit easier (if there is room) since you're crossmember is a lot better with more room.
I took my center exhaust hanger and made it face forward, then tweaked, and bent, and kept adjusting it until the 2.5" exhaust pipes were centered in the xmember holes. I actually ended up driiling holes in the exhaust hanger and dropped the clamp legs through there.... just to be able to keep the exhaust pipes centered. With you roomier crossmember you should have a bit more flexibility.
And the other option I found was the 1963 super fancy contraption. It also has the isolater between the bracket and the frame so it would work. Look at the drawing towards the bottomm
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
Here is what I did on my 82 four years ago with a Gforce Xmember and 700r4. All stainless 2.5" from collector back. eight bolts total including the collector bolts to drop entire exhaust in one piece. Makes it easiy to drop for the track.
Last edited by Buccaneer; May 4, 2019 at 04:56 PM.
although not the right fit for your TH700, the concept would be similar to fabricate something that attaches to the back of the trans using those bolts. the bracket is steel, long enough, has enough mass for heat dissipation, so that heat transmission to the trans is not an issue (the trans case is already pretty "warm"). the trans is rubber or polymer mounted to the frame, so NVH also isn't transmitted to the cabin.
I did something similar for my TH700 swap, had to do some cutting, sectioning, welding to come up with a bracket. can't take a pic because the car is not on jackstands (being driven).
also, I bought some SS 2.5" very tight bends to pie-section and weld up an S-shaped section of tubing to get around that pass side corner of the trans and still snake it through the stock 2-hole trans crossmember. it's a tight bend, it's a tight fit, wrapped with thermotec, but it fits, it works, no contact anywhere (except the bracket), and it's been on the car for years now. I might've started off with a small radius U-bend. you have to cheat on some of the turns and radius's. but it does make a smooth run around that difficult corner.
Finished up my support bracket; thanks for your info. Everything looks good & old exhaust came back in place; hopefully in the next few days I get to it finish up. Pending TV cable adjustment, converter lock switch wired in; & electric park/neutral switch. Transmission mount area
I did post pix of my install long time ago, so I describe it best I can....I have a welder buddy so that is a HUGE help, of course.....I started out with a 700 install in place of the Muncie 4 speed....'72 vette......so the cross support was cut about 4" from the side/frame rails....the 700 sat on the same forward extension plate the muncie used.....but the exhaust loops were cut open at bottom, and the rail cut back at an angle to open it up fairly wide, and capped off with steel, which is part of the support welded in under the top loops....so it has a vertical piece to top center of loops, and a cross piece from rail to rail just below the rail tops, the exhaust has more room to pass under the new frame arrangement so around the trans was no issue.....I changed over to a 200 4r later on, for other reasons, and so it sets on the rail directly, no forward plate needed......the shifter is a simple Hurst chrome rod mounted to the stock mount, and one of the rods used to go to the trans.....2" angle iron welded to cross support, top rear, similar/smaller to bottom rear, grabs the stubs still on the frame rails....drilled a hole for 1/2 inch bolt/locknut going fore/aft on each side.....about 6-7 bolts and the cross support is outta there......
Why do you think you need to support the exhaust there? (Real question, not a sarcastic one.)
I am using the arched Bowtie Overdrives 700r4 cross member and the exhaust just goes right under it like this. The only place I have the exhaust hung is off the back bumper.
Now I'm wondering whether they SHOULD have more support... I was just assuming that being connected to the heads on one end and the bumper at the other was "good enough"...
The exhaust should really be supported by the transmission side of the mount, not the crossmember side. By attaching the exhaust to the crossmember, the movement of the engine will stress the exhaust. If the exhaust support is attached to the transmission, the exhaust and the engine will move together.
and the way you are set up, it looks like you could run an almost straight steel plate across and bolt it to the clamps on the pipes and trans mount itself.
My first thoughts, I had concerns about stressing the exhaust manifold studs, also the factory exhaust support was in the same area, but attached directly to the transmission (400).
The 700r4 does not have that hold. With the G-Force support & transmission mount area, I just haven’t been able to configure a support bracket that would use the rubber flex of the mount, bracing from the top of the transmission mount.
I attempted not having the middle support, but the rear exhaust hangers allowed the exhaust ends to move side to side, which would claused the factory tips to hit.
700R4 Conversion Exhaust support
