Gm auto track transfer case question

[Striper80]

It has the motor on the front axle. All lights change on the dash and you hear the encoder motor changing the gears in the t case, It even goes into 4lo, but the front axle only engages in auto. I have no service 4wd message on the dash. Everything that was replaced was ordered directly from gm and is brand new.
The guy that did the work does all the work for the body shop I work at. He looked at it again but now wants to wash his hands of the job. I'm pissed that I painted a bumper for him and didn't half *** it.

[THEFERMANATOR]

Was the tccm programmed by the dealer? Pretty sure they come blank, and require service programming. When you say it goes into 4 low, does it go into low range? Trying to figure out if your issue is at the front axle or the transfer case. If it shifts into 4 low, does the driveshaft lock in and just not the front axle? There was an issue with the autotrac cases internally where the shift fork would wear out from running in auto 4x4. When it's in auto, it actually runs in 2 wheel drive, when the tccm see's a difference between the front and rear driveshaft speed, the tccm tell's the encoder motor to start applying pressure to the shift fork that engages the clutch pack in the transfer case to lock the front and rear shafts together. It's not a simple shift, it actually uses the shift motor to apply and hold pressure to engage the clutch pack via the shift fork, and overtime that fork can wear, and some have failed.

[Striper80]

The tccm was programmed by the guy that installed it. The worn shift fork seems like a real possibility. Once the snow melts a little I'll look into it further.
One thing to note is if I leave it in auto, then shut the truck off, the light on the dash goes to 4wd when I start it up. When left in 4wd, it goes to auto on start up.
If the case needs a rebuild how difficult is it? Any special tools? Seems a little more complicated than a reg t case without clutches.

[THEFERMANATOR]

The light changing on startup would make me think tccm. The tccm reads the position of the transfer case via the encoder motor, then the tccm turns on the appropriate light. If it's changing, that would mean the tccm is either reading the encoder position incorrectly, or the encoder is bad. I seen dorman is now selling a replacement encoder because the whole assembly is so expensive, and the encoder's do fail semi often(the most common failure in that system is the encoder). As to repairing the transfer case, I've never been inside a np246. The only full time cases I rebuilt were the np242 and np249, but they were a much more basic viscous clutch system.

[Striper80]

Was just under there changing my oil so I cycled it through a few times. The front shaft is locking and unlocking. Also didn't change when cycling the key. I couldn't jack it up today since my time was limited.

[THEFERMANATOR]

Originally Posted by Striper80

Was just under there changing my oil so I cycled it through a few times. The front shaft is locking and unlocking. Also didn't change when cycling the key. I couldn't jack it up today since my time was limited.

But that doesn't tell you if it's the front axle locking in, or the transfer case without jacking a tire up and spinning it.

[Striper80]

Originally Posted by THEFERMANATOR

But that doesn't tell you if it's the front axle locking in, or the transfer case without jacking a tire up and spinning it.

I hadn't thought of that. It locked in auto so if I had to guess I'd say the axle locked. I'll get the truck up in the air this week and look further. I think it's going to warm up a little bit.