Worried about transfer case.

[2001 yukon 2500]

I have a 2001 gmc yukon 2500 with the 8.1 and am worried about my transfer case a np 246. When I have been backing uphills recently it seams like my 4 hi will not engage. To test I did the standerd put truck into 4 hi and shut the truck off the lift one wheel to see if it spins. I did this and was then unable to spin the front tire by hand. But when I went to break the lugs lose with a bar I was able to spin the wheel with the truck off but still in 4 hi. I then put the truck into 4 lo and could not spin the tire. I was wondering if this was normal for the np 246 as I have seen in some spots online or if this means my transfer case is shot. It is also worth noting that after testing the 4 wheel drive I took it for a drive and in 4 hi I could feel the front end bind up as it should.

 

[strutaeng]

I have a 2001 gmc yukon 2500 with the 8.1 and am worried about my transfer case a np 246. When I have been backing uphills recently it seams like my 4 hi will not engage. To test I did the standerd put truck into 4 hi and shut the truck off the lift one wheel to see if it spins. I did this and was then unable to spin the front tire by hand. But when I went to break the lugs lose with a bar I was able to spin the wheel with the truck off but still in 4 hi. I then put the truck into 4 lo and could not spin the tire. I was wondering if this was normal for the np 246 as I have seen in some spots online or if this means my transfer case is shot. It is also worth noting that after testing the 4 wheel drive I took it for a drive and in 4 hi I could feel the front end bind up as it should.

Welcome to the gang.

I'm not familiar with that test procedure you are describing. Can you post a link to it or reference?

Does your truck do the same if you engage 4LO?

I'm by no means a transfer case expert, but this power transmission of this transfer case is both a chain and a clutchpack (actually a shared clutchpack from a different transmission.) I believe unless it's in AutoTrac mode, the clutchpack should be fully engaged and there shouldn't be any slippage. The chain is either a: it's there, or it's broken. It can't really slip.

I think the right way to test is by monitoring the speed sensors on the transfer case and compare them to the transmission output speed sensor. You will need an advanced scanner for that.

Have you checked that the blue transfer case fluid is at correct level?

 

[2001 yukon 2500]

I cannot remember were I saw the testing procedure but it helped me previously diagnose a bad front differential in the same truck. Also The chain in the transfer case is good as my 4 lo still works and I can feel the transfer case and front axle work and bind up as they should. I forgot to check the fluid level but will when the auto parts store opens. My thinking was that maybe the clutch pack in the transfer case went bad and is preventing the 4 hi from fully engaging as a I believe the clutch pack is part of the 4 hi but not 4 low in the transfer case.

 

[strutaeng]

I cannot remember were I saw the testing procedure but it helped me previously diagnose a bad front differential in the same truck. Also The chain in the transfer case is good as my 4 lo still works and I can feel the transfer case and front axle work and bind up as they should. I forgot to check the fluid level but will when the auto parts store opens. My thinking was that maybe the clutch pack in the transfer case went bad and is preventing the 4 hi from fully engaging as a I believe the clutch pack is part of the 4 hi but not 4 low in the transfer case.

Ah, ok. Have your ever serviced the transfer case fluid before? Maybe just drain the fluid and closely inspect the old fluid to see if you have any clutch material. Basically, threat it like a transmission.

Unless the fluid level is low. Look for that pump rub area (unless that has been previously addressed.)

 

[noodlesandsam2]

read this thread.

4 Wheel Hi In Reverse ?

Hey all. Quick question. I had had my truck in 4 wheel hi yesterday. I noticed the when I back up and cut the wheel the front diff. acts like a locker. It only does it in reverse. If I back up and cut the wheel to the right the right front tire will accutually completely lock up and slide then wi...

www.gm-trucks.com

As a follow up - I have had one of these trucks since 2002, and I use 4WD Hi infrequently - 2 or 3 times a year in deep snow.

I don't think I ever have used it in reverse - maybe straight out of a deep snow condition. Auto Trak would be my choice, not as extreme as 4Hi, but some safety net if you have slippage. With the 8.1, that guy produces a lot of down low torque. I've only had the 5.3, and now 6.0. My last big block motor was a 1979 Mercedes 6.9, and before that a 1970 Ford 429 FE. Maybe other 8.1 guys can add their experience.