I have a 96' 2500 - 4wd. You might know it snows once a year and the 4wd won't engage. The drive shaft to the transfer case turns when you put it in 4wd but the it won't engage - front wheels won't turn - the indicator light does not come on. In 2wd the shaft to the TC does not turn. I believe the 4wd is vacuum actuated but I don't know where to look for a vacuum line problem and could a vacuum line that works the 4wd have been accidently pulled loose while changing the a fuel filter or something like that...? Thanks for any advice.....

 

If I remember right, under the hood, just above the rear of the enginethere are two vaccum lines. They are the only two going down. The one on the left finds it's way to the front axle. Sounds like your axle isn't engaging.

Try that.

..Preston..

 

i would first check all vacuum lines going to the front axle passenger side actuator and also to the vacuum switch on the top left side of the transfer case. these can sometimes come loose. check the vacuum lines from the pump also to make sure they are not pinched anywhere. if all the lines seem to be ok then the actuator or the switch on the transfer case could be the problem...

 

Dustoff:

If the vacuum line to the transfer case was not on, how could the front drive shaft turn? How would it engage? Please explain. You have me cornfused.

..Preston..

 

Preston, actually when you pull the shifter the transfer case locks in. Therefore, the front shaft will turn. The vacuum to the rear slides a collar across the two piece axle, thus engaging the front axle. Cummins 96, start the truck, put it in 4x4, crawl under and where the shift rod connects to the transfer there are foour vacuum lines, pull the lines off (they can only go on one way,the plug is keyed), see if you have vacuum there, if you do, pull the two lines off the rear and see if you have vac. there. Process of elimination.

Hope this helps

Rick

 

check your vacuum lines on the frame comeing up from the axle disconnect when I put mine on the lift and the axle drops down it will come unplugged right there and if I don't remember to plug them in it does exactly as you say yours does.

 

I didn't get in last night until right at dark so I didn't have time to check all the vacuum lines out. I did notice one ( looked like 1\2" od ) line coming off the transfer case and dead ending right under and behind the air filter - it had what looked like a plastic one way valve attached to the end of it. Dust Off, Junk Yard and Bought a - I'm going to check and do all what you said. I'm pretty sure the problem is simple I just have to locate it. Thanks for all the advice and help. Does anyone know where there's a diagram of the transfer case that shows the vacuum lines, pumps, actuators and switches. It would help to see what I'm looking for.

 

I agree w/ Dustoff - It should just me the vacuum lines or the the front axle actuator. My Haynes actually has a decent breakdown on the transfer case - vacuum - front axle path. The front axle is not bad to work on, except to change the seals - kinda a pain, but your problem should be quick and easy.

 

4wd lives again.....!

I found the problem. It was an air line pinched from a recent trip to the shop to have some work done. I traced all the vacuum lines back from the transfer case - it was pinched right at the fire wall behind the wiring harness that go the fuel shutoff valve.

Thanks for the help and advice - it made the hunt alot easier.

Cummins

 

I found that my diaphram on the axel to engage the collar had filled up with gear oil and would not allw it to engage.