1994 GMC Sierra 2500

[Egglebl]

I have made a little progress on understanding the 4WD on my GMC2500. The Transfer Case seems to be functioning as I can feel the bite when I select 4WD from the cab.

The shaft leading to the front end is turning. I hae discovered there are what appear to be a couple of selenoides on the front pumpkin. I purchased a Haynes manual. It is not very helpful but it does identify these selenoid looking objects as thermal activator? There is an electrical connector leading to each one. When I have 4WD selected there is 12VDC at one of the connectors.

I feel the hubs are not engaging. Does anyone have any insight on this?

Thanks

[amac209]

power goes from the ignition switch to the fuse box to a switch in the transfercase to the front diff actuator(thing with 2 wires on the side) when the diff is actuated it closes another switch on top of the diff which turns on the 4wd light down by the shifter. it is common for the diff actuator to fail, i know mine did. lift both front wheels off the ground and put it in 4wd while the ignition is on, when you turn one wheel the other one will rotate the oposite direction if everythings working. if it isn't try removing the actuator(it unscrews) and check to see if it moves when shifting in and out of 4wd. if you have power and ground at the connector and the actuator doesn't move replace it. you can get an updated kit to install the new gm actuator used in the newer trucks. if the actuator works but the diff doesn't engage one of the shafts inside the diff is probably sheared off. hopefully this will help