Hey everyone - new user here -
I have a '99 Silverado with the NP246 (NVG 246) transfer case. It is sometimes called Auto-Trac and I believe GM has used it since about that time. It has 2HI / 4Hi / 4Lo / Auto Mode. There are no error codes from the TC / No "Service 4WD" messages and the front actuator seems to be working fine. The problem I'm having is that when 4Hi or 4Lo is selected the front wheels will turn if it's on a lift but not when there is a real load on them - seems an awful lot like the clutch pack is slipping. I saw the TSB about that problem a while back which stated the clutch pack had worn out prematurely due to cold weather and said to rebuild it. Being in MN I figured that may be it.

Here's what gets me - when I use Auto Mode the encoder motor will engage the clutches just fine and I've just used that for the last year. Pulls through snow - up hills - everything just fine. I know that the encoder motor will put a specific torque on the clutch pack in 4 Hi / Lo so as to lock the pack together and will vary it as necessary in Auto mode. So my question is - could the clutch pack be worn even though Auto mode works perfectly? Or could it be a sensor or something else that doesn't let the encoder fully engage the clutches when in 4Hi/Lo? I've had 2 shops look at it and they don't really know - just suggest replacing with rebuilt. I know some of you work on these and know their ins and outs. I searched hundreds of articles and posts and haven't found this specific condition. I would greatly appreciate any insight someone may have who is familiar with the inner workings of this transfer case.

Thanks
Chad

 

I am having the same problem with my 05 np246 not pulling in 4low. it works fine in auto and 4high. did you find a solution to your problem?

 

The OP Madchad's last login was November of 2008....... Good luck getting an answer from him. Private message him and see if his account still has an email attached that he still uses.