Author Topic: Seeking assistance on NP203 problem  (Read 4700 times)

Offline 1976er

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Seeking assistance on NP203 problem
« 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?

Offline Irish_Alley

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Re: Seeking assistance on NP203 problem
« Reply #1 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
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Offline Jason S

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Re: Seeking assistance on NP203 problem
« Reply #2 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?
1973 GMC K2500, Super Custom, Camper Special, 350, TH350, NP203, 4.10's
1974 Chevrolet K10, Custom Deluxe, 350, SM465, NP203, 3.73's

"1) Peace through strength; 2) Trust but verify; 3) Beware of evil in the modern world"

Offline 1976er

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Re: Seeking assistance on NP203 problem
« Reply #3 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.

Offline bake74

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Re: Seeking assistance on NP203 problem
« Reply #4 on: March 08, 2012, 05:58:43 AM »
  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.
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Offline Member161

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Re: Seeking assistance on NP203 problem
« Reply #5 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).

Offline Member161

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Re: Seeking assistance on NP203 problem
« Reply #6 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

Offline 1976er

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Re: Seeking assistance on NP203 problem
« Reply #7 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.

Offline Jason S

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Re: Seeking assistance on NP203 problem
« Reply #8 on: March 12, 2012, 11:27:11 PM »
Glad to hear it wasn't something catastrophic.
1973 GMC K2500, Super Custom, Camper Special, 350, TH350, NP203, 4.10's
1974 Chevrolet K10, Custom Deluxe, 350, SM465, NP203, 3.73's

"1) Peace through strength; 2) Trust but verify; 3) Beware of evil in the modern world"