GMC Transfer Case

Discussion in 'GM Powertrain' started by Diesel6_2, Apr 10, 2014.

  1. Diesel6_2

    Diesel6_2 New Member

    Hi! New to the forum and need information regards 1999 GMC Yukon transfer case. I've had the dealer read the code and they indicated the dash switch was bad. I'm certain that code was set when I pulled the switch assembly and took it to them to see if they could test or had a new one. Neither option could be covered. Bought new switch from Amazon and installed. No change. Ordered new shifter motor. Installed. Installation instructions indicate to install with transfer case in neutral. With old motor removed, you can shift the case to the various modes you want. After installation of new motor and vehicle on stands, started engine with AT in PARK. All OK. Shifted AT to neutral and pressed 4 LO switch. Shifted to 4 LO with no problem. Pressed 4HI; shifted, no problem. Pressed 2WH, shifted to two wheel. Tested wheels after each shift; proper wheels and drive shafts rotated when they were supposed to. Needed to
    clear the garage and go to bed. Next day fired it up, pressed 4HI, nothing happened. It will not shift again. My question is - has any one gone through the various shift points using a wrench? How many detent positions are there? How much torque do you think it should take to shift between the various positions. I expected 4 detent positions being 2WH, 4HI, 4L, N. I only found 3. Hope someone has been there, done that. Thanks in advance!
  2. Chesters

    Chesters Well-Known Member 2 Years ROTM Winner Gold Member 1000 Posts

    I cant be leave no one has gotten back to you on this. I really cant help much, just wondering why you installed it in neutral then when you started it put it into park. Can you hear the motor turning when in neutral engine off, and you hit the button?
  3. Diesel6_2

    Diesel6_2 New Member

  4. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    I also can not help you on this one. But, maybe [MENTION=54249]RayVoy[/MENTION] or @Jcat can. They seem pretty knowledgeable in this area.
  5. Diesel6_2

    Diesel6_2 New Member

    Thanks for looking! Hope one them looks and responds.
  6. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    @Pikey, thanks for the vote of confidenance; I know how they work (theory), but other than having to repair the front axle actuator in my previous truck, I have not had to tackle a repair on the transfer case.

    The theory part of me suggests that the problem may be in the transfer case control module (TCCM), these modules fail a lot more often than anything else (other than maybe the switch, depending upon model and year). In some trucks, it is in the passenger foot well, behind the trim panel.

    One other known problem area is the electrical connector at the transfer case, if water gets into the connector, the pins will corrode.
  7. Diesel6_2

    Diesel6_2 New Member

    Thanks RayVoy! Situation has changed a bit - after having driven it maybe 50 miles since last shift test, decided to try the buttons again. Lo an behold, it shifted! 2wh, 4wh, 4wl, N, & AWD. Backed out of the garage to test Hi & Lo range.
    I can hear the motor shifting each range and the proper lights come on. Only problem is the transfer case stays in Hi range. I'm convinced it's time to pull it out and check the innards. Any comments welcome before I do that! Follow-up dis-assembly of the old motor I found the brushes were running in an oil bath from grease that is in the planetary gear reduction assembly that the motor drives. Neat assembly! Three sets of planetary gears. Did not figure the ratio, but it's very high.

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