TH400 Questions - Whats the deal with NP205/NP203 versions?

[Mudzer]

I am installing a dual transfer case setup and have a TH400 with NP205 mated to it. I plan to install a NP203 range box on this tranny. What is involved in mating a NP203 TH400 version to a TH400 that was originally equipped with a NP205?

I read Watson's site and feel I understand, but just cant fathom why GM would offer two different versions of the TH400 for 4x4 Applications. Has anybody modified a TH400 originally equipped with an NP205 to accept an NP203? I realize I would have to drill and tap the face of the NP203 if I go this route. What about clocking the NP203 range box totally upside down for clearance, do I just drill the bolt pattern in how it will be clocked?

Thanks in advance.

 

[thatK30guy]

The output shafts on the 400's are both different lengths when mated to the 203 and 205.

RGF (Ralph) has pics of the 400 trannies on his webshots.com site. <a target="_blank" href=http://community.webshots.com/album/25992506ttLImcStQL>Pics from RGF's webshots.com site.</a> /forums/images/icons/wink.gif

 

[Mudzer]

Is the bolt pattern on a TH400 version NP203 the same as a TH400 version NP205? The pics help to understand this very well. Thanks Wes. Does anyone have a picture of a NP203 range box (the front mounting flange face) and the front face of a NP205 both for TH400 trannies? Just want to compare bolt patterns. If anyone has both adaptors, could you compare for me?

Thanks,

Neil

 

[thatK30guy]

If you mean the 400-bolt pattern, yes, they are a 6-bolt pattern.

It's just the shaft stickout on both that make them different.

 

[m j]

delete

 

[thatK30guy]

Plus...
the 400/203 adaptor is about an inch thick, while the 400/205 adaptor is about 4 1/2" thick.

 

[Mudzer]

Wes,

Im clear on the stick-out for the shaft, and am clear on the fact that all TH400 Trannies have the same bolt pattern on the back of the tranny. What I am not sure of is - Does the NP203 have a different bolt pattern than the NP205 (both being TH400 versions)? In viewing the Doubler setup you showed me pics of, I think they have different bolt patterns. Look at the Doubler adaptor, it has the round TH400 bolt pattern on it, and the NP203 stock adaptor seems to have a large shaped adaptor with fewer bolts.

I guess my only options are either drill and tap my NP203 box and live with the 4" extra length. This still should be less total length than a Gen1 Doubler. I am installing a CV rear shaft so driveshaft angles should not be a problem. With clocking the NP203 - 180 and Leveling the NP205, I should be able to get my skid plate as flat as Watson's.

Thanks for all the great info.

TheBigdaddyof2 is asking another question on the ORD board. What is involved in changing out any version NP203 range box to fit a TH400 tranny? Do you change the input gear only? Is it worth doing this swap? Is the TH400/NP203 range box a gold plated item (worth a lot of money)? I need to get other things started on this project and the info is great to have.

 

[thatK30guy]

Yes, the bolt patterns on the t-case side of 203 and 205 are both different.

I have a 400/203 adaptor laying in the garage. If you want to see a pic of it, let me know and I will e-mail it to you.

I used to have the 400/205 adaptor but sold it.

I wouldn't drill and tap the case to fit the adaptor. I would try to find the correct shaft and adaptor to mate everything correctly.

As far as BigDaddy goes, that's a very simple swap on the 203 input shaft to change from 27 to 32 spline. Just need to find the correct shaft though. I think ORD sells them.

Yeah, I guess you could say the 400/203 is a "gold plated item." /forums/images/icons/laugh.gif They were only available for three years. '77-'79, but the '77 models are even more rarer to find. '78 and '79 are pretty more common years, if you can find them. /forums/images/icons/wink.gif

I have a complete 400/203 combo sitting on the shed floor. /forums/images/icons/shocked.gif /forums/images/icons/wink.gif Interested in this?

 

[Mudzer]

Wes,

Thanks for the info, sounds good. You have a PM...

Neil