Binding when turning in Auto 4wd and noises

Discussion in 'General Chevy & GM Tech Questions' started by TJbear, Feb 19, 2013.

  1. TJbear

    TJbear New Member 100 Posts

    The other day, I had my truck in auto 4wd mode. The roads were mostly snow covered but there were some areas that were just wet. I rolled up to a 4 way stop sign where the road was just wet. I made a right hand turn after stopping and the drive-line binded up so bad, it was almost enough to stop the truck mid-turn!. It felt more like it was in 4wd high rather than auto mode. Made wierd rubbing/groaning noises. It made noise on turns before but never actually binded like that.

    I bought the truck with about 70k miles and it now has 104K. The drive-line has always been sorta "rough" and noisy but never binded up like that in auto. A couple years ago, I changed the diff and tcase fluids and replaced all the u-joints. Never noticed any excessive amount of metal "paste" on the drain plugs (none in the tcase). Truck "hums" even in 2wd when it's cold outside. Barely hear it in the summer. Auto makes more noise and 4wd high is very noisy in any temperature, especially when accelerating. I had thought the "hum", which seems like its coming from the front, was the wheel bearings, but I replaced both of those when the ABS sensors started acting up, and the sound was unchanged.

    I'm trying to narrow this down. I think the problem is all in the tcase BUT the humming sound at speed sounds like it's coming from the front. However, I know sounds/vibrations can sorta transmit along one part of the drive-line to another. One thing I do know is coming from the tcase is a ton of play/slop when shifting into reverse. When i put it in 4wd and shift to reverse, the slop is gone.

    Any tips on narrowing this down is appreciated.

  2. RayVoy

    RayVoy Active Member 1000 Posts 100 Posts

    When you select Auto4x4, the t-case clutches start to engage and a small amount of torque is sent forward (maybe 5%). When rear wheel slippage is detected, the clutches fully engage, splitting the torque font and rear.

    Sounds like you have more than "stand by" clutch engagement. One of the internal bearings has been know to fail, perhaps that is your problem.

    If the noise is coming from the front, perhaps a bad bearing in the front diff.
  3. TJbear

    TJbear New Member 100 Posts

    Interesting. The noise in 2wd from the front (or seemingly from the front) is mostly noticeable at around 50 mph+. If I'm cruising along at a steady 50-55 mph and hit the auto button, the noise goes away. :eyes:
  4. Pikey

    Pikey Moderator Staff Member 1000 Posts 100 Posts

    does the sound come from the drivers side?
  5. TJbear

    TJbear New Member 100 Posts

    Seems to be. Can sorta feel it through the floorboards when it's being really loud.
  6. Pikey

    Pikey Moderator Staff Member 1000 Posts 100 Posts

    I would take it to a ring and pinion shop.Most will check it out for free. I had a bad driverside bearing in my front diff. it made the same noise.
  7. MrShorty

    MrShorty Moderator 1000 Posts 100 Posts

    Check the t-case fluid. I had similar symptoms when I first bought my '98. Checked the fluid and it was pink, indicating someone had used Dex III rather than the blue AT2 fluid that it is supposed to use. Drain and refill with the correct fluid and it stopped binding up.

    I don't know if it stayed the same, but the fill plug on my tcase is a square 5/16" drive plug. I ended up buying a 3/8 socket adapter and grinding it down to 5/16 so it would fit.
  8. TJbear

    TJbear New Member 100 Posts

    Yeah, it may come to that. Just afraid its going to turn into an endless (and expensive) quest to fix the problem and still not succeed. I've read enough stories online of that happening to people with similar problems, which is why I've delayed fixing it for so long. Sorta testing the waters on getting a 2013 right now. It has some other issues, including totally rotted out rocker panels, and I'm not sure I want to dump thousands into a 13 year old truck. Stay tuned.

    I changed it a couple years ago and the proper stuff was in there. Checked it awhile ago and its still full.
  9. a.graham52

    a.graham52 New Member 100 Posts

    i thought auto 4x4 worked by leaving the front diff engauged (right axle shaft locked together) and then the trasfcase was 4x4/4x2 engaged as nessary? i belive if your front diff is engauged rather its 4x4 or 4x2 you will get the binding action.
  10. RayVoy

    RayVoy Active Member 1000 Posts 100 Posts

    I think I follow what your saying, and yes, in any of the 4WD positions, the front axle is engaged. Maybe using the AWD only trucks may be easier to follow.

    The trucks that only have AWD, do not have the passenger axle disconnect, both axles are connected to the front diff at all times.

    Although the front diff is an open diff, both axles connected to the diff will cause the front driveshaft to turn. As the front wheels turn in two different radius, which is also different than the rear turning radius, the front and rear driveshafts will turn at different rpms; therefore, internal t-case slippage is necessary to prevent binding.

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