th400 output shaft swap ???s

[lojones]

UPDATE: I found someone to help me with the swap

I havent had any luck finding any write-ups or online service manuals for a th400 so I took mine out and popped the cover off to have a look. It looks like you would pretty much have to disassemble the whole thing and pull it out the front

I have never been in to a automatic before, looks kinda scary. ive built an engine, setup my own gears and am pretty mechanically inclined so a few questions:

Is it advisable for me to start ripping it apart? does it take special tools? are there lots of little things i can fawk up? If i bought a book and said special tools how bout then?

If the answers are no, yes, yes, no then any suggestions? i called a couple shops and they want $400 to do the swap which would hurt my winter build budget too much.

I'd like to get this short output in there and get the Atlas hooked up.

 

[TreeClimber]

You have to disassemble completely to swap outputs on a TH400.

Why do you want to swap?

 

[lojones]

have a shiny atlas sitting on the floor that requires a 32 spline shorty output

 

[TreeClimber]

Yeah,

But what's in it now?

And the only reason I ask, is that TH400 mostly had the 32 spline shorty shaft to begin with. So why switch shafts when you should be switching the entire transmission?

I have two rigs. Both with TH400s & Atlas's. One's a AMC TH400, so I had to switch the output to a chevy short shaft. The other was a GM (out of a Suburban) and it had a short shaft from the factory.

GM trannys are relatively easy to find on Craigslists (search for "parting out" in the cars & trucks -or- in auto parts) and also at wrecking yards.

I'm thinkin' you've got a car tranny and it's way too long???

T

 

[lojones]

It's an AMC th400 so i have to swap the shafts. Yeah if i had a gm 400 i would just grab another trans that was in front of an np203.

 

[TreeClimber]

You're doing the exact same swap as I did. Yup, find a tranny guy. I had help from Jeeptech1 (he's a GM trained transmission specialist). Be aware that the AMC case and the Atlas tranny-to-transfercase do NOT line up the same as the Chevy case's do. There is a few degrees difference in the rotation of the bolt holes. AMC did this so that the quadratrac transfer case could clear the pan on the TH400. What this means to you is that once it's all installed, the rear transmission support will be off a few degrees from sitting flat. I used an axle/spring shim to level mine. Worked great. Also, use the poly rear bushing. I tried rubber first, but it collapsed in no time.

Good luck.

BTW, which Atlas you get? Mine's the 4.3 and it's a little too low. Wished I had the 3.8. And for references, it's an AMC 401 / TH400 / Atlas 4.3 / D60 with 4.56 gears and 37s.

T

 

[lojones]

Thanks for the info TC. I guess i posted too soon, a friend just called wanting to copy my EFI harness and hooked me up with their friend that will do the swap for me

I ran amc401 / th400 / d20 3.15 /44 w/ 5.38s and 35's which was just right for me.

I plan to move up to 60s w/ 410s or 456s and up to a 37 or 38.5 which will be close to where i was before.