Transfer Case Swap Help

Desertryder · 11-20-2009, 05:28 PM

I'm replacing my broke NP203 in my '76 GMC K15. The broke one is mated to
a TH350 auto trans. The working NP203 I found is mated to a TH400. Will it
be a straight across swap or are the two trannies different in some way? If
they are different, can I use anything from my TH350 to make it work?

hotrodpc · 11-20-2009, 06:27 PM

Quote:

Originally Posted by Desertryder

I'm replacing my broke NP203 in my '76 GMC K15. The broke one is mated to
a TH350 auto trans. The working NP203 I found is mated to a TH400. Will it
be a straight across swap or are the two trannies different in some way? If
they are different, can I use anything from my TH350 to make it work?

Hey DRyder, Welcome to the forum !!! I am not a 4x4 guru, but I can tell you the transmissions are differant. But, you should still be able to use the Tcase. You will have to use the original adapter from the original NP203 is all. Unless there is something else I am missing. I am sure someone more knowledgable will be here shortly to confirm or deny for you.

hotrodpc · 11-20-2009, 06:33 PM

OK, now I am backing up after re-reading the thread. Are you wanting the swap the transmissions too? Or are you taking the NP203 off the T400 and putting it on your T350? I am going to say, that is going to be the easiest solution. Take the NP203 off the T400 and bolt it to your T350, put it back together and you are done. JMO. Although, there is nothing keeping you from using the T400 either if you so choose. The crossmember is likely to have be moved back, but I'd imagine factory holes are there in the truck since GM is good about being universal. You can even use the same torque converter from the NON Lockup T350 to the T400. Cooling lines and shifter linkage will all be in the same spot. Vac line will move from rear of case to passenger side of case. Yokes are differant, but being you are hooking to a Tcase, that is unlikley a factor. Seems the crossmember and mount will be your only differance.

Desertryder · 11-20-2009, 06:47 PM

I am taking the NP203 off the TH400 and putting it on the TH350. Someone other than
from this forum told me the splines are different and would need to be addressed. I'm
confused and hope to find someone that's done this type of swap. Thanks for the info.

hotrodpc · 11-20-2009, 07:00 PM

Ahhhh, yes, that should be true. So what's the condition of the T400? If you are looking for a cheap way out, Install the 400 and NP203 together. But that may not be a cheap way out either if you have to mod the driveshaft to fit the tailshaft of the Tcase.

Desertryder · 11-20-2009, 07:01 PM

Much to my dismay the 400 is in pitiful shape.

bradrhale · 11-20-2009, 07:02 PM

the 350 has a 27 spline output shaft. the 400 has a 32 spline count. but i guess you could swap the 2 out. as stock, they wont switch out.

hotrodpc · 11-20-2009, 07:04 PM

How hard is it crack open the T cases and swap the output shafts?

bradrhale · 11-20-2009, 07:08 PM

how is that going to help?? the output shaft is what is needing changing to accept the 27 spline count of the tcase. question is how hard is it to change the output shaft of the tranny?? but that goes back to having to use the yoke out of the 203 case that he has robbed. either that or rob a tcase from another 350.

mudseeker · 11-20-2009, 07:10 PM

both 203 cases, correct? swap out the input shafts. easy peasy

11-20-2009, 05:28 PM	#1
Desertryder Junior Member Join Date: Nov 2009 Location: Casper, WY. Posts: 12	Transfer Case Swap Help I'm replacing my broke NP203 in my '76 GMC K15. The broke one is mated to a TH350 auto trans. The working NP203 I found is mated to a TH400. Will it be a straight across swap or are the two trannies different in some way? If they are different, can I use anything from my TH350 to make it work?

11-20-2009, 06:33 PM	#3
hotrodpc Senior Member Join Date: Jul 2008 Location: OK Posts: 6,932	OK, now I am backing up after re-reading the thread. Are you wanting the swap the transmissions too? Or are you taking the NP203 off the T400 and putting it on your T350? I am going to say, that is going to be the easiest solution. Take the NP203 off the T400 and bolt it to your T350, put it back together and you are done. JMO. Although, there is nothing keeping you from using the T400 either if you so choose. The crossmember is likely to have be moved back, but I'd imagine factory holes are there in the truck since GM is good about being universal. You can even use the same torque converter from the NON Lockup T350 to the T400. Cooling lines and shifter linkage will all be in the same spot. Vac line will move from rear of case to passenger side of case. Yokes are differant, but being you are hooking to a Tcase, that is unlikley a factor. Seems the crossmember and mount will be your only differance. __________________ *Winners NEVER Quit , Quitters NEVER Win !!!*

11-20-2009, 07:00 PM	#5
hotrodpc Senior Member Join Date: Jul 2008 Location: OK Posts: 6,932	Ahhhh, yes, that should be true. So what's the condition of the T400? If you are looking for a cheap way out, Install the 400 and NP203 together. But that may not be a cheap way out either if you have to mod the driveshaft to fit the tailshaft of the Tcase. __________________ *Winners NEVER Quit , Quitters NEVER Win !!!*

11-20-2009, 07:04 PM	#8
hotrodpc Senior Member Join Date: Jul 2008 Location: OK Posts: 6,932	How hard is it crack open the T cases and swap the output shafts? __________________ *Winners NEVER Quit , Quitters NEVER Win !!!*

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

11-20-2009, 06:47 PM	#4
Desertryder Junior Member Join Date: Nov 2009 Location: Casper, WY. Posts: 12	I am taking the NP203 off the TH400 and putting it on the TH350. Someone other than from this forum told me the splines are different and would need to be addressed. I'm confused and hope to find someone that's done this type of swap. Thanks for the info.

11-20-2009, 07:01 PM	#6
Desertryder Junior Member Join Date: Nov 2009 Location: Casper, WY. Posts: 12	Much to my dismay the 400 is in pitiful shape.

11-20-2009, 07:02 PM	#7
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 9,511	the 350 has a 27 spline output shaft. the 400 has a 32 spline count. but i guess you could swap the 2 out. as stock, they wont switch out.

11-20-2009, 07:08 PM	#9
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 9,511	how is that going to help?? the output shaft is what is needing changing to accept the 27 spline count of the tcase. question is how hard is it to change the output shaft of the tranny?? but that goes back to having to use the yoke out of the 203 case that he has robbed. either that or rob a tcase from another 350.

11-20-2009, 07:10 PM	#10
mudseeker Senior Moderator Join Date: Feb 2006 Location: michigan Posts: 7,155	both 203 cases, correct? swap out the input shafts. easy peasy

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Transfer case?	greasemonkey	Chevy Truck Forum	4	05-24-2009 09:29 PM
Need Transfer Case help,, please	Just 1 More	Chevy Truck Forum	1	05-13-2008 05:30 PM
'98 Transfer case	mont91	Chevy Truck Forum	3	05-22-2007 11:10 AM
Transfer Case	flossy2259	Dodge Truck Forum	0	08-08-2006 04:00 PM
transfer case	guidorr73	Dodge Truck Forum	2	12-12-2005 05:39 AM