TH400 SWAP HELP

[fast_n_low86]

Ok, so I just recently put a 7.4L in my truck and withing the same day cooked the 700r4 I was running behind it (knew it was going to happen). I just went and picked up a th400 to replace the pile of s#!* 700r4. I've never had one in this truck and it's a 1976 rv th400 behind a 1975 454.

What am I going to need to do to hook this up in er and get it running well. I'm already aware of torque converter change. I'm seeing the 400 is shorter then the th350 and 700r4. So driveshaft seems imminent.

I'm not sure what the linkage on the gear selector is for and if I need it. If I do how would I connect that.

 

[NickTransmissions]

No clue if you need the linkage either but you will know one way or another once you install it. I'd start by swapping the U-shaped braket from your 700R4 to your TH400. You'll need to run a wire and connector for the TH400's detent solenoid, otherwise you may have upshifting or downshifting issues. The TH400 should not be shorter than a TH350; its roughly the same length as a 700R4, not counting the extension housings (no idea if you have a 2WD or 4WD since you left that out).

Beyond that, hope you wont be trying to drive this thing on the hwy too much as your RPMs in third gear are going to likely be 3k or more at 65 mph, depending on final drive (no idea what that is either since you didn't mention it).

Lastly, if the TH400 is from an RV origionally, it may actually be a TH475, which had straight cut plantetaries and a different output shaft than any other TH400 which allowed for the attachment of a large drum-style parking brake.

What are the letters and numbers on the metal ID tag?

 

[fast_n_low86]

Will send pics of the metal tag and what not shortly

 

[fast_n_low86]

So it's on a rwd 1986 c1500 gmc, running with 3.42 gears in my rear-end with limited slip.

 

[NickTransmissions]

Yep that is a TH400, not a Th475...That said, it may have 6 clutches in the direct drum and 5 in the forward, which was pretty standard fare for Motor Home/Box Truck/School Bus applications. You likely have helical gears, not the straight cut but that's not a big deal.

Good luck with the project.