Transfer case issues

Dragnduster

Original poster
Member
Oct 27, 2012
2
First post for a newbie so here it goes. Hopefully Roadie will see this or anyone else with ideas or thoughts please reply. Just bought an 03 TB a couple months ago for a commuter ride to work, I work at a mine at 8600' elev and definitely need 4WD in the winter. Here is what it does, it will shift into all the different positions of the transfer case properly without any troubles, in A4WD the fronts kick in when sensing rear slip properly and seems to work correctly. When I put it in 4HI or 4LO on slick conditions it will spin the rear tires and not seem to have any pulling from the front tires. If I put it on jack stands and put in 4HI or 4LO the fronts will spin when in gear(at idle) but I can physically stop the fronts by wedging a block under the one side to stop it and grabbing the other front spinning tire with my hands and stop it(just like the wet clutch in the transfer case is now slipping). Should the TCCM adjust for wet clutch wear in 4HI and 4LO like it does on A4WD? If not is there anyway to adjust the engagement pressure on the wet clutch when in 4HI or 4LO so that it locks in solidly like I think it should? I hate to replace a transfer case if it is not needed, but I would prefer to use 4HI on the snowy mountain roads I travel over using A4WD. Thank you Roadie for all your help to this point getting things figured out. Thanks for any help all of you can give me with this.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I remain stumped why A4WD can clutch up, but 4HI and 4LO fail to. I got home after the hurricane, and just checked the shop manual in more detail.

It says:

"The NVG226 requires no clutch shimming. The TCCM controls for the wear of the clutch and different clutch torque levels. The software learns adapt ready positions, which are for the correct clutch torque. The learned adapt ready positions vary as the unit wears over its life."

Not enough details to understand the algorithms, and GM neglected to send me the code for review when they were designing it. :wink:

A GM Tech II tool could command the encoder motor to go to specific positions, and read back the position feedback sensor to see if there were problems. There's a slight chance that the encoder motor sensor is dirty or has a damages spot, and reports to the TCCM when it's in the desired 4HI position when it's not, but that's not consistent with a dead 4LO mode as well, since the encoder motor is in widely different positions for those two modes. If only you had a buddy to swap encoder motors with for an experiment.
 

Dragnduster

Original poster
Member
Oct 27, 2012
2
Thanks roadie for the help, I do wish there was someone nearby I could swap encoders with and see for sure. I pulled my encoder off, left the wires hooked up, and could watch it turn when activated with the dash switch. I am just having a hard time understanding that the TCCM will adjust for clutch wear when in A4WD but not in 4HI or 4LO. Wouldn't the adjustment that the TCCM makes for wear in A4WD be where it would be set for 4HI and 4LO, or is there a default setting that the wet clutch returns to each time? If I could only figure out how to get the wet clutch to have the same pressure on it when in 4HI and 4LO as it does in A4WD then I would be a happy man. Any chance that the TCCM is having issues and causing me the problems? Just not looking forward to changing out a transfer case.
 

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