4x4 not engaging

[terryjsmith]

Hi all,

 

I have a 2000 Chevy Silverado Extended Cab with a 4.8L engine. I recently noticed the 4x4 wasn't working; I can hear some stuff working but the front wheels are never engaged. I have had the truck for a couple months and haven't tested it extensively before this. It has an automatic shifter.

 

I've done some quick testing and when I lift the front of the truck, I can spin front tires manually when 4x4 is engaged. In 4LO there is certainly more resistance and I can hear/feel the gears switching and in both 4HI and 4LO I can see the drive train turning but not in 2HI (which I think is what I expect wrt to the drive train). I assume the front tires should not be manually turnable in 4WD.

 

In my testing, the pin on the axel actuator does come out and I can hear the shift motor working on the transfer case. I wasn't sure what it was (I'm still not), but I replaced the shift motor just in case and the result is the same.

 

So I've checked: the fuses, the axel actuator and the shift motor and now I am out of ideas an open to any last minute suggestions before bringing it to the dealer to diagnose. I understand there is also a control motor I can replace for another $100 or so in the dash but would like to know if that's likely to be the issue before taking any more guesses.

 

Thanks!

 

Terry

[LongrangeLauber]

If you here the motors working then its probably something to do with either the actuator motor on the front diff. or maybe the little fork assembly that locks in the passenger side tire is shot. I'm no expert so I'm sure someone will chime in here soon. I actually need to pull my front diff. so I can get it rebuilt. Damn shop ripped me off

[dodge123]

I had a bent mainshaft in the transfer case. I forget how much out of tolerance it was but on a lathe it was visibly "messed up". It caused the actuator motor to make noises but not change into any gear. The cause of that was the driveshaft yoke in the case had worn the tail bushing out enough to bend the mainshaft. I self diagnosed and replaced all parts though. Hopefully your issue isnt that serious.

 

A quick check just for the heck of it would be to get under the truck and try to push up and down, vertically or side to side on the rear driveshaft just where it meets the transfer case. There should be no movement in any direction. This may indicate the bushing just behind the black oil seal is worn.

[gmtech4]

I had a bent mainshaft in the transfer case. I forget how much out of tolerance it was but on a lathe it was visibly "messed up". It caused the actuator motor to make noises but not change into any gear. The cause of that was the driveshaft yoke in the case had worn the tail bushing out enough to bend the mainshaft. I self diagnosed and replaced all parts though. Hopefully your issue isnt that serious.

 

A quick check just for the heck of it would be to get under the truck and try to push up and down, vertically or side to side on the rear driveshaft just where it meets the transfer case. There should be no movement in any direction. This may indicate the bushing just behind the black oil seal is worn.

sorry ,wrong info sir ,,,,you can move the rear output driveshaft of the tcase

[dodge123]

Your right. The driveshaft slides in and out as it should. I was just saying other than that, I dont believe there should be any slop where the yoke spins around the bushing inside.