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Johhny 09-23-2014 04:24 AM

NP203 input shaft swap?
Hey everyone, hope someone can help me out with this,

I got a '79 4x4 Suburban with a 400ci, th400 and a np203 transfer case. The np203 broke a while ago (worn chain) so I got myself a new one from a '78 Sub.

After removing the old np203 and installing the new one it appears to have a different input shaft. After some online research I discovered that apparently:

np203 for a th400 = 32 spline input
np203 for a th350 = 27 spline input

Since the old one only has a worn chain I was wondering if I can swap the input shaft to the new case? Did anyone did this before? What steps are needed? Will the axles still fit?

Since most Subs here are 2wd it was already hard to get a GM np203, so getting another np203 is kinda hard. If anyone knows any other solutions please let me know.

Old np203:

New np203:

68Timber 09-24-2014 06:54 PM

Re: NP203 input shaft swap?
I would contact Advanced Adapters, they'll know for sure, but I suspect they'll interchange. As for swapping it out, I couldn't help there, I get cross-eyed when someone takes a transfer case apart. But I'm guessing the service manual will walk you through it.

Johhny 09-25-2014 03:30 AM

Re: NP203 input shaft swap?
You were correct, they do interchange. I ran into a new problem tho:

I disassembled the old np203:

took out the input drive gear (32 spline):

and placed it in the new tcase:

Everything fits perfectly but I can't seem to reassemble the range box case...

There's a lever with shaft combined with a lockout shift that's located in the range box case itself:

The lever with shaft goes on 1, the lockout shift goes on 2:

I have no idea how to connected this when putting the case on, it al has to connect when the case is already half on, anyone has any suggestions?

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