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73-87 Chevy _ GMC Trucks => 4 Wheel Drives => Topic started by: 1976er on March 06, 2012, 09:53:14 pm

Title: Seeking assistance on NP203 problem
Post by: 1976er on March 06, 2012, 09:53:14 pm

Still looking for clues.  76 Chev 3/4 ton, full time 4X4, NP203 transfer case.  Transfer case will jump out of HiLoc at the slightest jolt or bump, even going from reverse to drive.  Linkage is correctly adjusted, I went so far as to unhook linkage at the case housing and shifted to HiLoc manually at the case and it still jumps out of Loc upon going in reverse and back to drive.  Any ideas before I tear into the case?

Title: Re: Seeking assistance on NP203 problem
Post by: Irish_Alley on March 07, 2012, 02:21:57 am

thinking its not going to be a simple fix, and you will have to tear into her

Title: Re: Seeking assistance on NP203 problem
Post by: Jason S on March 07, 2012, 08:06:10 pm

What happens if you try Lo-Loc? 

When you manually move the lever on the T-case, does it feel like it's positively locking in or does it just freely go into position?

Title: Re: Seeking assistance on NP203 problem
Post by: 1976er on March 07, 2012, 08:21:05 pm

Actually I have not tried the LoLock position as I seldom use it and I figure if there is a problem with HiLock I am going to have to open the case anyway to see what the problem might be.  My local parts dealer used to work for GM and thinks the problem might be a worn or bent shift fork.  Yes, does feel to positively engage when I shifted to HiLock by hand at the case.

Title: Re: Seeking assistance on NP203 problem
Post by: bake74 on March 08, 2012, 05:58:43 am

Quote from: 1976er on March 07, 2012, 08:21:05 pm

  My local parts dealer used to work for GM and thinks the problem might be a worn or bent shift fork. 

      After reading about the adjustments and linkage steps you took, my first guess would have been the shift fork also.  It looks like you are going to have to tear into the case, make sure you inspect all the shift forks carefully, if one is bent the possibility of more being bent is very high.

Title: Re: Seeking assistance on NP203 problem
Post by: Member161 on March 12, 2012, 07:36:46 pm

Ball-spring detent, spring is weak(best case) or shifter rail
detent is worn out(worst case).

Title: Re: Seeking assistance on NP203 problem
Post by: Member161 on March 12, 2012, 07:52:54 pm

Sorry, never used this before. I put a stiffer spring in my
203 & it helped a ton. If it pops out of Hi-Loc, cheat the
adjustment to engage Hi-Loc sooner.

1976 GMC K25, purchased 1999, 350 crate motor, TH400,
NP203, no lockouts

Title: Re: Seeking assistance on NP203 problem
Post by: 1976er on March 12, 2012, 10:58:48 pm

Opened her up and found the problem.  One of the smaller bearings (pinion?) and adjustment shim were disentergrated and lodged in the gears.  Now just need to get her back together.  Appreciate all the input from everyone.

Title: Re: Seeking assistance on NP203 problem
Post by: Jason S on March 12, 2012, 11:27:11 pm

Glad to hear it wasn't something catastrophic.