The fourwheel drive " on the fly" system will engage, via a clutch pack, when the computer system senses one output shaft is turning faster than the other. This engagement will only last a few seconds and drops out automatically. Fourwheel drive "lock" is an actual gear to gear engagement that is controlled by 2 motors, one for 4wheel in/out-one for high/low. The "lock" position should not engage or be engaged above 4 mph ie. Almost stopped. If it does try to engage above 4 mph, the gears in the transfer case will not have sufficient time to fully engage and they will grind or not mesh at all. If this has been allowed to happen continuosly, the mesh side of the gears may have become worn or chewed up which further restricts their ability to mesh. Bottom line, assuming the shift module has already been replaced, I would look at the internals of the TCase or consider replacing it.
The pump lubricates all of the components on the TC main shaft. If this pump is restricted or has failed, it could cause the problems you have described. But, usually by the time you find this out, the internal damage has already been done. In these TC's the pickup tube for the pump has been known to split, causing little or no fluid supply to the main shaft.
Friday, October 10th, 2008 AT 3:07 PM