Help needed cross member mod 350/700R4
Thread Starter
Burning Brakes
Joined: Feb 2009
Posts: 780
Likes: 1
From: Shelby NC
Help needed cross member mod 350/700R4
I've searched and found info but not specific on x-member mod for 350 to 700r4 using original x-member. Lots have used bowtie x-members but no one said this is what I had to do to use the original x-member. I need someone to say this is what I had to do--any pics? Issues are mount holes, emergency brake cable mount, exhaust (I'm using true duals not y-pipe on a 77 model car). Someone had shown a comparison diagram on mount location on different trans and the difference on a 350 to 700R4 is not much. Looks as if holes could be modified to fit that but I have not done this yet. Just don't want any surprises!
Thanks for any help!!
Thanks for any help!!
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
i am not sure why you would want to use the original crosmember its big and really heavy, i used the BTO one just for simplicity sake. i suppose you could make one out of tube steel easy enough though. if you do this you will need to move the brake cable pulley. i would be more inclined to make one then try to use the original one. let me see if i have any side by side comparison photos.
Last edited by bobs77vet; Jan 5, 2010 at 04:22 PM.
Melting Slicks
Joined: Aug 2004
Posts: 2,914
Likes: 229
From: Oakbank Manitoba
You can buy a bolt on perch for the original cross member. Here are a couple of pictures of the one "Bowtie Overdrive" used to sell. I sold mine recently. There is still a company selling one....I'll see if I can find out who it was.
Melting Slicks
Joined: Aug 2004
Posts: 2,914
Likes: 229
From: Oakbank Manitoba
Here is a link to a perch that is made for your conversion with the stock crossmember.
http://www.fourthgearinc.com/Corvette_Conversions.htm
http://www.fourthgearinc.com/Corvette_Conversions.htm
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
That is the exact perch that is used for the TKO conversions using the stock cross member. I just removed mine. I'm going to have to mod my cross member for the T56 now. It moves it back another 5.5 inches or so.
Thread Starter
Burning Brakes
Joined: Feb 2009
Posts: 780
Likes: 1
From: Shelby NC
Will you use the part for yours--just moving it back on your x-member?
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Burning Brakes
Joined: Feb 2009
Posts: 780
Likes: 1
From: Shelby NC
That's one of my issues also--what about the exhaust pipe. I have true duals and they are chambered pipes and that square corner on the 700R4 on the rh rear corner is not like the 350. I guess something will have to be re-bent or slight curve put in it.
Melting Slicks
Joined: Dec 2009
Posts: 3,233
Likes: 657
From: Thunder Bay
I don't remember the exact measurements of the modification I made when I put a 700R4 in my 79, but I cut a couple of inches out of the crossmember outboard of the exhaust hole on the passenger side, and welded it in inboard. This moved the exhaust hole out without changing the length of the crossmember. This allows the exhaust on the passenger side to clear the transmission. You will also have to cut the emergency brake pulley bracket off the crossmember and reposition it. Not a big deal. just grind off the weld, trial assemble everything to figure out where it has to go and weld it back on. You can get all the brackets you need to mount the trans to the stock crossmember by getting the parts from an 82. The General used the 700R4 in these.
Thread Starter
Burning Brakes
Joined: Feb 2009
Posts: 780
Likes: 1
From: Shelby NC
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
My Muncie car had a very similar mounting plate/extension on it too, I got it welded up/modified for the 700 I had in there....later went to a 200 so still have the plate....some time ago, I got tired of fighting the exhaust when doing anything with the tranny, so I cut/removed the welded in cross support, fixed it with L channel stock on each end, and a fore/aft 1/2" bolt to secure it in place, in the exhaust loops/holes, I cut them back really good, keyhole shaped, and formed some bridge work across the open channel and a support to the top of the old loop steel....
put that back in with the pipes now free to drop out from the bottom for all the clearance necessary to get that support and tranny outta there, just like a NORMAL car....
put that back in with the pipes now free to drop out from the bottom for all the clearance necessary to get that support and tranny outta there, just like a NORMAL car....
Thread Starter
Burning Brakes
Joined: Feb 2009
Posts: 780
Likes: 1
From: Shelby NC
Thanks guys- I guess the original idea was the best. Get an older xmember used with the TH400 and use the 200 4R????? I've got the 700R4 and I guess I'm committed to it.
Anyone know if you use the Bowtie type xmember does the exhaust fit OK? That xmember is open under it so the pipes would have nothing to interfear with?????
Anyone know if you use the Bowtie type xmember does the exhaust fit OK? That xmember is open under it so the pipes would have nothing to interfear with?????
Melting Slicks
Joined: Dec 2009
Posts: 3,233
Likes: 657
From: Thunder Bay
I don't remember exactly, but it was only about an inch or two. If you move it too far the exhaust pipe will interfere with the trans tunnel, as I recall. Once you have the trans bolted to the crossmember, get under the car and have a look. It will be pretty obvious where you have to position the crossmember exhaust hole to get the exhaust to clear the trans and tunnel.
