Shops, Barns, Varmints, and Trucks - NP 246 transfer case on GMC

Print Page | Close Window

NP 246 transfer case on GMC

Printed From: Unofficial Allis
Category: Other Topics
Forum Name: Shops, Barns, Varmints, and Trucks
Forum Description: anything you want to talk about except politics
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=166673
Printed Date: 09 Sep 2025 at 5:39am
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: NP 246 transfer case on GMC

Posted By: Coke-in-MN
Subject: NP 246 transfer case on GMC
Date Posted: 15 Dec 2019 at 9:06pm

Had the input bearing on front differential go bad and just rebuilt that but after installing it - 4 WD transfer case will not go into 4 wheel mode
The unit is the NP 246 unit with 4 button electric dash switches -
It's not showing any service 4 Wheel unit light and the lights on dash buttons do flash when shifting - indexing motor seems to run on the transfer case but no 4 wheel high or low - in auto mode still now 4 wheel - just 2 wheel drive
Odd thing is when that front bearing went bad it locked up truck so it would not move in 4 wheel but shifting out to 2 wheel and truck moved fine - now in any mode the buttons are set to it only has 2 wheel drive - no low range or anything putting power to front differential

Unit is on my 2000 GMC 2500 HD with the 6.0 engine and HD transmission -
When I first got the truck new the transfer case did this under warranty and the unit was replaced as they said clutch pack was set up wrong from factory -
This time it makes me wonder if clutch pack went bad again but somehow changing front differential bearings should not affect transfer case - yes the front motor on transfer case is engaging front axle -
Is there a way to test or reset the logic program in the controller or a code that shows what is wrong .

-------------
Life lesson: If you’re being chased by a lion, you’re on a horse, to the left of you is a giraffe and on the right is a unicorn, what do you do? You stop drinking and get off the carousel.

Replies:

Posted By: HD6GTOM
Date Posted: 15 Dec 2019 at 11:36pm

I am not personally familular with them. I do know the guys in the shop at the car dealership replaced a lot of the push button units. Good luck with yours.

Posted By: shameless dude
Date Posted: 16 Dec 2019 at 3:04am

check the thingy up under the front of the bumper, it's the thing that slams a shaft back and forth to put it in and out of 4x4, don't put your fingers up in there cuz if it happens to engage you won't have them any more. dang...I wish I could remember what it's called! simple to replace, also check your push button switch.

Posted By: Coke-in-MN
Date Posted: 16 Dec 2019 at 9:25am

actuator motor on front axle is working as when 4 wheel is pushed on switch motor advances axle lock ring and then when you turn one wheel by hand the opposite side turns other direaction - so spider gears are engaged as is axle .
Can feel the motor on the transfer case run - but to which position it engages the shift forks or applies pressure to the clutch pack - unsure .
Replaced the switch group a few years back -
Is there a way to reflash the module that controls the 4 wheel - or find any codes

Posted By: shameless dude
Date Posted: 17 Dec 2019 at 12:06am

actuator is what I was trying to think of! to late now tho...actuator=thingy! lol I hear a lot of folks say they had to replace the push buttons switch on the dash, I've never had to yet, so I don't know how it would act.

Posted By: Coke-in-MN
Date Posted: 18 Dec 2019 at 3:01pm

Picked up another NP246 unit last night from guy a couple miles from here - he had a 4L80e transmission and t case he wanted to sell as a unit, said he would not split it - someone offered him a good price for trany so he split it and called me if i wanted the case - so now to put it in and hope it works -
Seems used units from junk yard are around $600 and rebuilt units around $1400 - called one place said he had rebuilt for $650 - plus core .
So now figure out if the unit is good as he said he got it from friend and it all worked good when he bought it .
I replaced the buttons a few years back on the truck - just hope when i get done they were not the problem as no one seems to be able to diagnose why a unit isnt working