th400 with 208 adapter?

[down4thakrown]

I just picked this th400 with what I think is a 208 adapter for 50$ am I correct? Could I use this adapter on my 208 that was behind a 700r4 with the right input swapped in? How are 208's towing? I'm goin to use this tranny in my tow truck. Or could I use this tranny/shaft with my 203 dbler if I got a th400/203 adapter.

 

[down4thakrown]

Pics

 

[big dan]

np208s from th400s have a 32 spline input. so you would either need a np208 from a th400 or sm465 or swap the inputs like you said.

you can also find a late model 32 spline np205 with the round bolt pattern and it will bolt up to you're th400 with the adapter you have.

for the np203 you would need an np203 with a 32 spline input and the correct adapter.

As for the strength of the np208, there are lots of different opinions about them. Ive never had anything in my trucks but 208s. I have 205s and 203s laying around but never saw any point in swapping. Currently I have one in my trail rig that's clocked flat and Im working on a slip yoke eliminator for it. My dd also has one with a sm465 and an ls motor and Im real hard on it. Even towed a load to the scrapper that weighed 14000 (that's truck and trailer included) and regularly tow lighter loads and never had trouble. I think as long as you don't smack the case on something you'll be fine.

 

[down4thakrown]

I got the 32spline 203. I just wasn't sure if the tranny shaft is too long. Found this on Ord after I posted

GM TH400 Automatic Transmission:
If you have a TH400, there are three options for mating the 203 to your trans.

1: Use a factory configuration. The TH400 was available with the NP203 in heavier duty trucks (3/4 and 1-ton generally) in approximately '78-'79. The factory configuration uses a 1 3/8" stickout 32 spline shaft in the TH400, a 32 spline input gear in the NP203 and a 1.1" adapter plate between the two, somewhat similar to the TH350 adapter plate. This is the shortest way to mate the TH400 and NP203.

2: Use a TH400 that originally had an NP208 mated to it. This TH400 uses a 32 spline shaft that sticks out of the case about 2.5" and has an adapter housing that's about 2.5" thick. You'll use a TH400 version 32 spline input gear in the NP203 and re-drill and tap the face of the NP203 with the round bolt pattern to match up to the NP208 adapter housing. Benefits of this kit are the parts are quite common since the NP208 was very widely used with TH400 trannies. The drawback is the adapter is about 1.5" longer than the shorter factory configuration.

3: Use a TH400 that originally had a NP205 behind it. This TH400 uses a 32 spline shaft that sticks out about 4.5". You'll need to use a factory TH400 to round pattern NP205 adapter housing that is 4" thick and once again, re-drill the front face of the NP203 to match the round pattern. The input gear will be the TH400 version NP203 32 spline input. Drawbacks to this system are the overall length with the 4" housing between the two and the expense of buying the factory housing. They're not common as used parts and typically must be purchased new. ORD can supply this adapter.

 

[big dan]

I was under the impression that the outputs were the same length but Ive never messed with a th400. Just learned something new.

 

[diesel4me]

I bought a spare NP208 with what I was told is a TH400 adapter (round with 6 bolts)..someone told me it'll also bolt right up to a SM465 with the 32 spline output shaft from about 82 -87 too?...

One of these days I'm going to pull the short tailshaft housing off the 74 monte-carlo TH400 I have in my shed,and see if it'll couple up to the NP208,with no spacers or cutting the shaft shorter..looks like it might fit ,going by a tape measure,but I wont know for sure till I try mating them up I guess..