Engine/Transmission (1998.5 - 2002) Front axle will not go into 4 wheel drive

[Big John]

I have a '99 3500 4x4 that the front axle will not go into 4-wheel drive. The transfer case shifts fine, but I cannot get a 4x4 light and the axle is not pulling. Anyone have a similar problem/solution? I think it might be the vacuum module on top of the transfer case. I am ignorant of how these fail, as I have had 3 Dodges since '94 and all have gone over 200,000 miles with no shifting problems. This current truck has 199,000 plus miles.



Looking forward to some help.



Big John

 

[RRees]

I had a 99 V10 4x4 before I purchased my 06 Diesel.



In my case, it wouldn't shift because of a leak in the vacuum line near the frame rail. I found the leak by taking the hose ends off of the shift motor on the front axle and used compressed air to find the leak.



If that doesn't work for you. That is, find a leak. Remove the front shift motor and check to see if it works. Sometimes the shiftfork will break. Not likely, but it can happen.



Good luck.

 

[DFerverda]

Big John, if the cad doesn't hookup check the vacuum line. Does the air cond blow out the dash vents? If not it is disconnected by the vacuum pump or beside the brake booster, look at those 2 locations first. The vacuum pump is just in front of the power steering unit.
If you have vacuum there, crawl under the truck and unhook the cad (center axle disconnect) on the passenger side of the front axle and see if it is pulling there.
Dirk

 

[y-knot]

The most usual place to have a vacuum leek is the supply lines the go down to the transfer case and the control line which go from the transfer case to the axle, they run along the passenger side. You can also UN-plug the CAD vacuum connection and use a vacuum pump to see weather the CAD system is engaging and dis-engaging.

 

[Big John]

Thanks everyone for the replies. I had previously checked for leaks and found none. I took the time to remove the vacuum motor at the front axle. It has good vacuum going to it and will slide the fork when off. I did find some slight burrs on the axle end on the driver side, but nothing that should stop the slide. Even when off and actuated, I still do not get a 4x4 light!? I also think that the diaphram has a crack or hole in it because it pulls a suction on the downstream side when connected to the vacuum line on the other side of the diaphram.



Still puzzled. Still looking. Will have some time to check out more this weekend.



Is it possible to rebuild this or is it strickly a swap?



Big John

 

[Big John]

Update: Vacuum motor was bad. Leak in diaphram. Replaced and shifts fine. Total cost $231. 00. Took about 30 minutes.



thanks again for replies.



Big John