Help with diagnosing 4X4 problems '97 K2500 Suburban

[Roberth1970]

Hi, I was wondering if anyone can help me with diagnosing my 4X4 problem?



Symptom: No power/torque to front wheels when 4X4 is activated. This has worked in the last month, but as I discovered in a snowy parking lot, it's not now (chains to the rescue).



Vehicle: 1997 Suburban k2500 - 454 vortec, 4L80E, NP243c Transfer case (push button, 2HI,4HI,4LO). 130k miles.



Indicator lights: all the lights work as expected, pressing into 4HI the light comes on, same as into 4LO.



Stepper motors: noises can be heard from the front diff and the transfer case.



Tests so far: I have raised the truck off the ground (securely onto axle stands).



1) 2HI - rear wheels drive

2) 4HI - front wheels drive but can be easily stopped by a gloved hand.

3) Removed and checked that the diff actuator motor is working

4) With the engine off, and in neutral 4HI the two front wheels seem to be diff locked (rotating one counter rotates the other). I have not been able to test this with any force. In 2HI the wheels are unlocked.



Things I have not tested yet but will tonight:



1) I didn't notice if in 4HI driving if both wheels stopped when I manually stopped one wheel - I'm thinking that if only one wheel stops then the front diff is at fault.

2) I haven't checked what the front input shaft is doing when I stop the front wheels - if the input shaft stops turning then it's probably a problem at the transfer case?



Can anyone give me any more tests to help diagnose the problem?



I was really hoping it was the front actuator motor - but it looks like it's not. If it's the transfer case then replacement looks 'interesting' as one of the cross members in the way has the torsion bar socket/mounting.



Thanks all.

 

[rcb1]

I would suspect the t case. The chain may be jumping or the sprocket to shaft is severely worn.

 

[clubber]

I just broke the case of my NP243 case a couple of days ago because the chain was worn out. I thought I had a while to repair it because it didn't appear to be too bad yet. I got a very mild scraping noise under acceleration for about a week of short commuting before it blowed up really good. I was going to change it in another week but it didn't make it that long. I'm just telling you so if it's T-case, you get it fixed before it gets way more expensive. Good luck and know you may not have very long to fix it.