Grinding T-Case Shift

[DDiesel]

I changed the oil in my 2001 Chevy T-Case last spring. I refilled the case with ATF. This Winter I've had problems with it grinding when I shift into 4x4 on the go. (Push button case) No grinding when truck is stopped. I haven't ruled out front axle actuator but pretty sure it's coming from T case. Did ATF damage something? Planning to change to Autotrac oil. If that doesn't help then should I swap out shift motor with another truck before dropping the T-case out for repair?

[DmaxMaverick]

I would not recommend changing the fluid to Autotrac. Not only will it do nothing to help your current condition, it isn't a recommended fluid for your TC. ATF is the recommended fluid, and serves well. Your TC was designed to operate with Dexron III fluid.

The grinding can be caused by several things. Most common on vehicles using the "shift on the fly" option at highway speeds A LOT, is a worn synchro (their usefulness is finite). Changing the fluid type will likely make this worse. Another possibility is a weak motor, delaying engagement (not timing with the synchro and front diff). If front diff engagement is having issues, it can cause the TC to clash on engagement, defeating the synchro function.

[DDiesel]

My understanding of the owner's manual is that ATF was for the manual shift cases & Autotrac was for electronic shift cases. Either way, the oil would not be the issue?

[DmaxMaverick]

My understanding of the owner's manual is that ATF was for the manual shift cases & Autotrac was for electronic shift cases. Either way, the oil would not be the issue?

That statement is correct. If you have a 2500HD or a 3500, you have a MANUAL transfer case, as far as the fluid goes. Push button or not, it is shifted manually, and the only electronics involved is monitoring and range shift prevention (in case all required conditions aren't met). Autotrac II fluid is recommended for those with "Auto 4x4" (and a corresponding button on the dash). Your TC is shifted mechanically, after you manually push the button. Auto 4x4 is a comprehensive system that shifts in/out of 4x4 according to traction conditions, if so selected. Auto 4x4 is only available on 1/2 and 3/4 ton (non-HD) GM trucks.

If you use Dexron III (or later) fluid, it is not the issue. Perhaps if you used a fluid not recommended, like motor or gear oil, or an ATF rating not recommended.

[DDiesel]

Ah, gotcha! A matter of terminology confusion on my part. Thanks for clarifying.

[DDiesel]

Ok. The ATF is not the culprit. What next? Should I swap shift motor with my other truck to see if it behaves correctly? How do I check the front axle actuator? Do I just need to scan for codes?

[DmaxMaverick]

If you have the option to swap motors (most don't without a bunch of cash), I'd start there. The price is right, and they are not difficult.

I don't know about the front axle test, short of actually sitting in your seat and "feeling" the timing and engagement. Difficult to break into words. You can use a scanner to read engagement timing and line voltage values, but most common scanners (non Tech-II or high-end Snap-On) won't be of any help. Ranges have to be pretty far out of range before codes will be present. If you aren't seeing the "Service 4wd" message, it is within the specified ranges. Unfortunately, the monitoring system won't detect gear clash or indicate a possible system failure in this case, that I've seen.

[DDiesel]

Well, this morning I swapped front axle shift motor with another truck. It didn't help anything. The "clunk" and or "grinding" is definetly coming from the Tcase. I was going to persue swapping out the shift motor on the case with the other truck next. I removed the three lower screws around the motor but it still felt firm. Do I need to remove the cover opposite the motor, on the drivers side of the case or am I missing something else?

[DmaxMaverick]

The front shaft should be removed and the TC should be in Neutral during the R/R of the motor assy. I've done it this way every time, so I don't know if it works otherwise (manual recommends it). It should come loose with little force. The gasket may be sticking. It is soft (silicone?), so be careful. I don't know the availability without a new motor assy. You should be able to reuse it if it's clean and undamaged.

The 3 mounting bolts torque at 15 ft/lb.

[JohnC]

Just out of curiosity, if the front axle is engaged, the tires are all the same size, and the truck is going in a straight line and no wheels are spinning, what's to grind?

[DDiesel]

Good question. I've pondered that also. Anyone?

[DmaxMaverick]

Good question. I've pondered that also. Anyone?

The reason I suggested the front diff/motor. In any case, the TC shouldn't grind. The front diff engagement is usually delayed upon selection of 4x4 (and every time with a manual floor shift TC).

[DDiesel]

Forgot to update this post. I swapped the shift motor out and seems to shift better. Thanks.