TH400 Identification - 2WD vs 4WD...

[Greg72]

I feel like I should have learned this by now, but I guess it wasn't "personal" enough to me yet!

Now it is.....


I've got a TH400 sitting in my garage, all built and ready to install. I "assumed" it was a 4WD version, but now I'm not so sure. What are the differences between the 2WD and 4WD TH400s? Is it the bolt pattern on the trailhousing? Overall length? Output shaft stickout?

I put a straightedge across the case and carefully measured the stickout of the output shaft (32-spline) and I got 4-5/8" (4.625"). I'm not sure if this clarifies anything....

 

[83ZZ502_Jimmy]

Could be 2 possiblilities.

1. - It could be a 2wd case. I have one behind my ZZ502 without issue.

2. - It could be a 4wd case that mates to a 205.

The 4.5" (4.625) is the giveaway here for these two options. Also, do you have a large/cast bolt on bottom bellhousing, or just a stamped steel one? The larger, cast one is 4wd.

At any rate, I would not hesitate to run a 2wd case in my rig.

Hope it helps,
John

 

[Greg72]

I have a cast cover for the bottom bellhousing, but it might not have been from this specific tranny.

Ultimately, I'm just trying to understand how 2WD or 4WD makes any difference when it comes to buying an adapter?? If the hole patterns were different somehow, I could understand.

I'm ultimately trying to connect this to the new Atlas4, but I need to specify the correct adapter......and don't know the answer yet.

 

[83ZZ502_Jimmy]

The output bolt pattern of all the TH400's I've seen is the same. This should not create any adapter issues.

 

[muddybuddy]

i know the difference between the 700r4's is output length, maybe the 400 is the same, not sure

 

[HarryH3]

All Turbo 400's have the 6-bolt hex pattern on the back. They just have a tailshaft bolted on in 2WD applications. The main difference is in the tailshaft length. You'll need to talk with the adapter folks to determine if they have something that will work with your output shaft.

 

[Jimbo*]

Never fear Greg, the cases are fundamentally the same for 2wd or 4wd. In fact, the "K" case (with the cast flywheel cover) wasn't dreamed up 'till about 1980 or so--which is to say the early K30 Th400/NP205 setups were "car" trannies. Your output shaft length dictates you use a cast tall adapter, and a 205 with a short 32 spline input gear.
Hope this helps, Jimbo

 

[mikey_d05]

There's no difference between the bolt patterns of the tail housings. I'm running an NP241 behind a 2wd BOP TH400 in my rig. All the 4wd stuff just dropped in.

 

[Greg72]

Well OK......I guess I'm confused as to why Jesse is asking about 2WD vs 4WD versions??? The only thing that seems to matter is the stickout measurement.

 

[mikey_d05]

AFAIK, 2wd 32 spline is the same as 4wd 32 spline. Both of the 2wd output shafts I had fit snugly into the 32 spline t-case input.

 

[fireplug]

Subscribing...

 

[johnnychimpo]

Here's a pic of the output shafts, hope it helps.

 

[folkenheath]

About the rear adaptor, don't worry about it, all TH400s have the 6 bolt circular rear adaptor like others mentioned. The only thing you need to worry about is how much the the tailshaft sticks out of the housing. 4 1/2" is correct for a 2WD short tailshaft, or a 4WD with the "early" NP205 adaptor. Around 1985 they switched to the shorter version (2 1/2") to match with the new manual trans output shafts, which I believe is the same for the NP208 t-case. The NP203 version only sticks out around 1 3/8". So you either have a 2WD short tailshaft, or a 4WD early NP205 version. The tailshafts are the same. The only difference in the actual trans case is where the torque converter cover bolts on. Look at the front of the trans case on the bottom, if it only has 2 bolts per side, 1/4" I believe, it is a 2WD case, if it has 3 bolts per side (3/8" or 7/16" bolts), then it is a 4WD case.
With that said, you can still run a 2WD case in a 4WD truck without any issues.

 

[Greg72]

Here's a pic of the output shafts, hope it helps.

Thanks, that document helps a LOT!

The TH400 in my garage has the TWO sets of helical cut gears at the base (only some of the shafts in the pics have two, so that narrows it down!) and based on the total stickout, and the position of the rubber o-ring near the splines, I'd say that mine must be the one in the upper left of that photo.

In any case (no pun intended), Jesse at High Angle seems to have found the correct adapter for me, so things are one step closer.

Thanks to everyone for the help on this one.