Transfer Case Skipping? 09 Tahoe LTZ

[PatDTN]

So the neighbors are sure I'm crazy but low range works. Hopefully it's back in normal mode now.

Maybe I'll luck out and having shifted into low range and back it'll be cured. I'll know that tomorrow.

 

[02Lightning]

I think I would suspect the actuator on the transfer case not fully engaging, maybe change the fluid in the transfer case and see if you can find any metal.

 

[sprinter]

So when in 4x low and you drive around a bit (I mean even 20 feet forward and back) do you notice the same type of condition as in regular 2x mode? Does it appear to be skipping? When you shift between modes, do you get any errors on the display or does a "service engine soon" come on? If your light is already on, check the codes for direction. Failing that, try to differentiate if it's coming from the back or front. It's important as it starts narrowing down your problem. But check both differentials for fluid. It's a relatively easy step and good preventative maintenance if all is well.

 

[PatDTN]

Okay, some more information.

This morning I left home with the selector in auto. Just climbing out my driveway it thumped some.

I drove a couple of miles and it was the same problem. Then I twisted the selector over to 2wd and drove. Problem gone. I did some backroads driving at both ends of my trip and a bunch of interstate and no problem.

Almost home I twisted it back over to auto. The problem is there.

So. Is something making it think I have a rear wheel slipping and it's dialing in 4wd for me? Is there no hysteresis to keep it from jumping in and out? I know my right rear axle leaks oil. Can that cause a bad sensor reading? I had a BMW that would collect metal shavings on the wheel speed sensor and mess up. Anything like that on these?

I'm getting closer. At least now when I put it in 2wd it doesn't do it. Note that I tried that before and had the problem still. Shifting down to 4wd low and around seems to have changed things. I watched a YouTube video about changing a control box under the dash. Maybe mine is bad?

Thanks again for the thoughtful help on this.

 

[Christoph559]

I think I would suspect the actuator on the transfer case not fully engaging, maybe change the fluid in the transfer case and see if you can find any metal.

This. I just changed my fluid yesterday bought two quarts from local gm shop 22$, make sure it has the correct fluid

 

[Jason_S]

Depending on how much use your transfer case has seen, it is possible for the chain to "stretch" some and allow skipping. Changing the fluid wouldn't hurt, and would allow you to see how much, if any, metal is in the fluid. The correct fluid for your transfer case is a dealer only item and is a blue/turquoise color. On some transfer cases, you can also check you chain slack through the fill hole. I just do not remember off the top of my head if that is possible with this transfer case.

The rear seal is not a hard job and could be done in the drive way in an afternoon (probably 2 or 3 hr for the first time). No 'special' tools required. It is also a relatively inexpensive repair. The cost of changing the fluid in your rear differential plus the cost of a seal (~$10-15). The LTZ comes with the limited slip rear differential, but it does not require a friction modifier. I tend to just use a good GL-5 gear oil.

EDIT: if you find chunks or slivers of plastic in the transfer case fluid, that is from the chain guides.

 

[PatDTN]

Haven't changed my fluid but did get some more data.

First I drove on a relatively smooth gravel road in auto mode. I think I can still feel the skipping. Unfortunately 4x4 also feels the same, maybe it's skipping maybe it's bumps.

I had another thought. If it's sensing wheel speeds and comparing front to rear to decide I may have caused this by rotating my tires. I bought this with nearly worn out Wranglers on the front and some other brand of newer tires on the rear. The Wranglers would tramline on spray painted lines in the road and are noisy. So I rotated my tires to get the newer tires on the front.

Given the wear plus the difference in brands I wonder if the rolling diameter is off enough to make it think the littler rears are spinning and it needs to shift into 4x4? I don't remember feeling this when I test drove it and I can't recall feeling it before I rotated. Thoughts? Obviously I could swap the tires back but I don't want to.

 

[PatDTN]

I finally bought a full set of new Michelins and at least for the moment the problem is gone. I'm sticking with the theory of different diameter fron and rear tires making the transfer case keep shifting in and out of 4wd.

 

[Brian Wilson]

Any new info on this?

 

[PatDTN]

The skipping feeling is definitely gone. I've been able to use my auto 4wd setting any time I want. I used it on I81 tonight running 75 to ..uh.. 90 with no problem. That was in heavy rain. Ive used it in the dry as well. I'm calling it a tire diameter problem.