So I'm out 'wheeling in the desert this weekend and I come up on some rocks. I have the darndest time getting over them. My front wheels don't want to drive. I'm teetering on 2 wheels and my right rear is spinning away (obviously my LS is a little worn and needs some attention) and my fronts are doing nothing. Finally after some rock building and some muscle pushing the bumper I was over and through.

I figured that since I was so cockeyed that I had bound up the front, no biggie I've done that before. Next I'm in the soft stuff and my rear end starts bucking and spinning (wheel hop). Nothing from the front (no spinning). So I put it in 2Hi then back in 4Hi and, viola, my front end started working and made it through no problem.

My question is this: why would my 4wd drop out? My front hubs were locked any my 4x4 light was on. Even when I shifted in and out of 4Lo I could hear (and feel) my transfer case clunk during the shift. But after a period of time my front wheels would stop driving. What gives? Has anybody experienced this before? I had no indications besides my rear wheel hop in the sand.

The weird part was that nothing changed (no noise, my hubs were still locked and my 4x4 light did not go out). I have never had a problem with the transfer case side of the 4x4 so I am not very familiar with it. I will check the connections with the 4x4 module and relay (?). Can anybody tell me where they are?

Any help would be appreciated. I have never heard of this kind of problem before.

 

You might want to service your autolock hubs. Its unlikely its a vacuum issue since it uses vacuum pulses to lock and unlock them and not constant pressure. I would concentrate on the TC. It seems like your locked and in 4x4 and not getting the energy to the front wheels. Servicing the hubs is still a good idea anyways! Takes little time and energy. I dont have experience with the transfer case other than draining and refilling fluid.

 

I believe the PHVS (Pulse Hub Vacuum Solenoid) should send vacuum pulses to the hubs intermittently to keep them locked. How often I do not know.

 

It pulses when you go into 4wd and when you go back into 2wd. My hubs were locked and my 4x4 light was on. I went through a couple of vacuum leaks when I first bought the truck so I know that's okay (new hubs x 2 with new seals, new solenoid and new vacuum lines from the solenoid to the hubs on both sides). I even got out and verified that the hubs were locked (knuckles would not spin). I know my TC has a higher stall speed due to it being a diesel but never had a problem with the wheels not driving on the flats. And when I did have that problem, using 4Lo solved any issues.

I'm going to search and try and find the location of the module and relay but has anybody heard of this particular instance where the front wheels just stopped driving?

 

Take a look on the side of your T case. Check the motor and the connector. There is a possibility that something is loose.

 

References to TC in this thread mean Transfer Case.