1996 4x4 not engaging(np231)

[old head]

My front axle is not engaging. It is the manual np231 transfer case. There is vacuum at front actuator and cable moves. No fluid in lines. Front actuator cable housing is broken but inner cable is good. Could this be it? Also when transfer case is engaged, the front drive shaft spins by hand, from what I read on here this means transfer case is not engaging either. What could this be? All vacuum lines good and free of leaks. Can someone please help? I can't afford to replace parts intermittently.

[old_master]

The NP231 is a "shift on the fly" transfer case. Meaning that you can shift from 2WD HI to 4WD HI without stopping the vehicle. The vehicle must be stopped to shift into 4WD LO. Whenever the vehicle is in motion, the front driveshaft is turning. In 2WD the shaft is driven by the left front wheel. In 4WD it is powered by the transfer case. When you shift to 4WD, the vacuum actuator pulls the cable in and locks the right front axle to the differential and the axle becomes live. When 4WD is engaged you should not be able to turn the driveshaft by hand. There is something wrong in the transfer case if you can.

[old head]

Old master, I just purchased the truck, so I don't know the history, but I do know the tranny was rebuilt recently(4l60) is there anything you can add as to what could be wrong with the transfer case? The driveshaft spins freely in any 4x4 position so does this mean it must be serviced professionally or are there any quick fixes I could try? You are truly the master! Actually it even free spins just sitting in park, just checked.

[old_master]

Just to clarify, you do have the manual transfer case shift lever on the floor console, correct? If you shift to 4WD LO, does the LO range actually engage? Keep in mind that with the front driveshaft turning freely, only the rear wheels will be powered. This will determine if the transfer case is able to shift the range from HI to LO.

With the engine at idle: If you can apply and release the vacuum at the actuator by moving the shifter from 2WD to 4WD and back to 2WD, it means the linkage inside the transfer case is at least operating the vacuum switch and all of the vacuum lines are good.

[old_master]

This web site has some good information and shows an exploded view of the case along with a parts list and overhaul kit.

http://www.drivetrain.com/parts_cata...rts/np231.html

[old head]

Yes it is the floor shift. The case does go into 4lo no problem or noises, just no front engagement. When I engage the 4x4 the actuator pulls in and holds vacuum. The outer shell of the actuator line is broken, but the inner steel cable is good. When I drive on snow in 4x4 sometimes it feels like the front wheels are actually pulling but it could be my imagination. However at no time that I have checked the front driveshaft it is locked in.(always free spins) If the chain is broke in the case would that cause this? How hard is that to replace? Thanks

[old head]

I just talked to my transmission guy, he says what he has found in 90% of these situations when the front driveshaft isn't engaging it's worn pads on the shift fork or broken fork. Do you think this is true.

[old_master]

If the case is quiet, I doubt if the chain or a sprocket is damaged. You were able to change the range from HI to LO, so that part is working. It's the mode that you are unable to change. In the link that I posted above, part #49 in the exploded view is the mode fork. There is a real possibility that it is worn or broken, or who knows what. It could even be something with the linkage too. What ever the problem is, it will require removing the transfer case, taking it apart and inspecting it. Not difficult, just time consuming. If you're going to try it yourself, I would recommend having a shop manual to guide you through it. An alternative would be a rebuilt case or a used one.