Swapping from a 3-speed to an OD

[SStephen]

I recently bought a '85 GMC 2500 from a friend of mine. He bought it with a bad transmission and never got around to fixing it. It runs great and I want to use it for a work truck. I need to stop putting all those "towing" miles on my Suburban and stop using it as my work truck. Amazingly, it's still in great shape!

My question is that I have a recently rebuilt 700-R4 from a '85 Camaro that I was going to install in my '87 Monte Carlo. If I can use it for the 2500, I will. What are the problems I will be running into if I do the swap? My first guess is that the crossmember and tailhousing are different, the speedo will be off, and possibly a different driveshaft? I'm up for the task but I just want to hear from somebody who has done the swap or just knows whats involved. I will be doing some towing and possibly some heavy loads every once in awhile. I don't see having the TH-400 rebuilt if I already have an OD sitting in the garage. Also, any downfalls from having the OD? I just like the idea of lower RPM = better gas mileage. Thanks in advance.

[Jonboy]

you will need a TV cable bracket, and a TV cable, if the trans is out of a TPI car. You may also need to swap out the tailshaft housing. The Camaro housing has the pattern for a torque arm, and the mount provision is different, I think. I know it needs to be swapped on the Vette trans for sure. Also look into getting something to work teh TCC. I used the painless kit in my Blazer. Seems to work OK. I think there is some more info to do it cheaper in Jeff's site-www.73-87.com . You will need to move the crossmember back also, and have a new driveshaft biult.

On my 77 Blazer, I swapped out the TH350 for a 700R4. I had an 82 Blazer with everything, so I swapped it straight over. I used the column, so you can pull it down into 1st, the trans (duh), and the driveshaft. My truck has headers, and I couldn't get teh 700 trans crossmember to cooperate, so I used the one from the TH350. It wasn't really too bad. Keep in mind that you would have to make the same modifications to your Monte, so it really is no big deal.

[SanitysBane]

i've used camero and truck transmissions, theres really no difference between them besides the extra holes, either can be used, i have never seen a corvette 700R4 but i am pretty shure that they are differnt.