[95 S_Trucker]

Out of curiosity, do you have a 3 button 4wd switch(NP243) or a 4 button 4wd switch(NP246)?

The NP246 is more problematic. When you shift into 4wd, do the yellow lights on the switch light up solid, or do they flash?


You can check to see if the problem is in the front diff or the transfer case

Chock the rear wheels
Jack up the front of the truck and put it on jack stands.
Turn the ignition on but do not start it.
Leave it in park, and shift to 4wd High
Can you spin the front drive shaft? if you can't, your transfer case/shift motor is working.

If you can, you have a problem in your transfer case/shift motor


While its up in the air and in 4wd, try and spin the front wheels at the same time. If they don't move(or they move only when the driveshaft turns) the axle is engaging.

If it doesn't engage, you may have an actuator problem(pretty common) or the shift fork/bushings are worn out in the differential(not super common, but it still happens)

The actuator can be replaced without removing the differential.

The shift fork/bushings require the differential to be removed.



***The Np246 transfer case has clutches in it, If they are partially worn, everything will test ok when trying to turn stuff by hand, but it will slip when trying to push a big suburban.***