Posted by Dimsdale on February 24, 03 at 11:12:48:
In Reply to: THANKS! posted by Dan on February 20, 03 at 11:48:56:
Traveler hit all the notes in his responses. The input the computer receives for "slippage" comes from a comparison of the front and rear output shaft speed sensors on the transfer case (or wherever they are), so a tight turn will give enough of a difference to make the computer think you are slipping and not simply turning. Running with AUTO on will only decrease your mileage by an mpg or so, and increase front end wear to a degree. It is no different than running with an older four wheeler with the hubs locked and the transfer case in 2HI, which is what we did when it looked like the weather was going to turn. AUTO simply selects 4HI temporarily for you so you don't have to pull the lever. If you activate it a lot, it will shift into 4HI by itself to minimize wear on the transfer case clutches. I believe it will still disengage from this setting by itself, but don't quote me on that.
When I first got my '99 Sub with Auto4WD, it would snap and bang on sharp corners. It was much more alarming than taking the same turn in 4HI. There is a recall for a different type of Autotrac fluid. It is a blue fluid obtainable at the dealership. Do not use ATF (unless they have modified the transfer case to accept it without trouble. There is another modification that involves a nickel plated output slip shaft that is supposed to alleviate the banging. Banging, snapping, bucking etc., is NOT normal!
The Autotrak II blue fluid did the trick for me. While I can feel it engage on a really tight turn in AUTO, there is no banging or anything weird. The front axle engages nicely when the rear wheels spin.
As an aside, the AUTO setting gives you the opportunity to run with the axle and front driveshaft engaged during the summer if you normally only use the 4WD in winter. This is like running with the hub "in" in an older four wheeler periodically to distribute the lube in the front end and keep seals from sticking. You can't do this easily with a non-AUTO equipped truck. Maybe the newer trucks don't really need it, but I have always done it with my old Scouts and Blazers, and it definitely never hurt anything. The owner's manuals used to recommend it, saying to run about 12 miles with the hubs locked and in 2HI.
: Tony, Thanks a ton for the info. Think I will drive another one with the sales guy and listen to see if I'm just hearing normal 4WD noises.