Engine/Transmission (1998.5 - 2002) 4wd lo but no 4wd hi?

[esommer2500]

My 4wd quit working in hi-range a couple months ago, but still works in lo. Did some searches and figured it was either a vacuum problem or the switch on top of the trans case. Bought a new switch from dealer ($35) and put the truck up on stands to change it out and test - still no 4wd in hi-range, but the front driveshaft is spinning. 4wd lo works like it always has. Took CAD off (broke three of the four bolts) and tested for vacuum leak and movement of the shift fork, which seemed to be fine - free movement of the shift collar when vacuum is applied to the lines. Cleaned up the CAD and reinstalled, thinking at this point it would have to be a problem with the shift linkage, like it is moving the arm on the t-case far enough to engage the gears for the driveshaft to spin, but not far enough to detent the ball on the bottom of the new switch to engage the vacuum and operate the CAD. Adjusted the linkage four different times in both directions in 1/4" increments to no avail. Even took the boot off around the shift lever in the cab to make sure there wasn't something there obstructing the movement when pulled to 4wd hi-range, which there wasn't.



Any thoughts?



Only other option I see at this point is going to a posi-lock system if I can't get this figured out.



TIA



Eric

 

[NIsaacs]

Is it possible you just think it is in working in 4/lo? That the transfercase is shifting down but still not engaging the axle. If that is the case, you might have a broken axle.



Nick

 

[esommer2500]

I don't think so, mostly due to the fact that I was testing while the truck was on jack stands in the shop. Drop it in 4lo and all four wheels spin. 4hi spins the rear wheels and the front driveshaft, but not the front tires.



Eric

 

[cerberusiam]

From your description, the CAD is simply not engaging in 4Hi for whatever reason. If the front drive shaft is spinning and a wheel isn't the axle shaft is disconnected.