I tried to pull my boat out yesterday and my truck wouldn't shift into 4 wheel drive. Shift lever operates but light on dash does not come on and truck is not in 4wd. Had to start truck up the boat ramp with the boat pushing to get me off the slick stuff.

 

Check to see if any of your vacuum lines have come off.

 

More info, looks like all of the lines are connected but they don't have the best connections as they are stretched somewhat. Checked the vacuum at the diaphragm at the axle and have vacuum on one side. Shifted the lever inside the cab and lost vacuum on that side but did not get vacuum to oposite side as I expected. Took the shift fork off and applied vacuum to diaphram with a vacuum pump and it holds vacuum on both sides of the diaphram but the fork does not move. I thought it would when I applied vacuum to the oposite side. Any suggestions where to look next. I also turned the hoses around and expected the fork to move and it stays in the same position. The sliding coupler on the axel is free and can be moved with my fingers. I don't understand why I can't move the fork when it is removed. I have not taken the shift fork, and diaphram mechanism apart.

 

The fork may not shift unless the tire is spinning.

 

I expected the shift fork to move with the engine running and the fork mechanism removed from the axel. I know the ends of the axel need to line up for the sliding colar to align with both ends of the axel, but with nothing in the way and no axels involved the shift motor or diaphram does not move the fork, but the diaphram does not leak.

 

Took the fork/shifting mechanism to the bench and gave the fork a couple of raps with a wooden dowel. Got the fork to move towards the switch which shows the 4 wheel drive is engaged. It seemed to be stuck and after it moved I had to give it a couple of raps to get it to move back. After exercising it a couple of times I was able to get the fork to move with vacuum applied with my vacuum pump. It will now pull it both ways. Installed shift fork and motor back on axel and drove truck around my cul-de-sac in both directions to get it to shift. Still no luck, as mentioned earlier one side had vacuum the side to take it out of 4 wd but the other side gets no vacuum when moving the shift lever in the cab. I will trace this back to the top of the tranny where the valve is that shifts the vacuum from one tube to the other. Anyone know where that is located or how you get to it?

 

Does anyone have the diagrahm of the control valve for the 4 wheel drive shift control at the tranny

 

I don't have the diagram, but the vacuum router is threaded into the top of the transfer case with 4 vacuum lines going to it, at least that's how it is on first gens. It was a bear to get at on my ram. Dodge has them pretty cheap-maybe 20 bucks. I actually saw one in the 'HELP' section at advance auto yesterday for fifteen. There's a steel check ball of sorts in there that gets stuck causing the vacuum not to change when you engage the x-fer case lever. Hope this helps.
greg

 

I had a leak at the switch on top of the transfure case. there is a molded plug that was cracked cut the vac lines off and pluged them into switch was not easy to find leak.

 

OK guys, I had the truck in some deep salt water and the molded connectors at the front axel were loose enough to suck some salt water into the system. It corroded the fork vacuum motor housing freezing the fork and also formed a salt plug in the formed tubing which goes across the frame to the opposite side of the transmission. Got rid of the sticky fork and removed the salt plug with some salt remover I use on my fishing reels and everything works again. Thanks for the help. I am replacing the molded tubing at the axel end of the system. I will just use vacuum hose at this time and see how much Dodge wants for the plastic and neophrene casted piece.

 

I replaced the switch and the plug and lines at the same time. I think the total was around $65. At first I just replaced the switch, but the old plug didn't want to seal to the new switch so I got a new plug, the lines come with it. It was well worth it. Works great all the time.

 

How do you get to the switch if you want to replace it? It appears to be on top of the transmission. Did you go through the floor around the shift levers?

 

You can unscrew the switch from under the truck without any major problems. Make sure your vacuum lines are clean - don't have oil in them from the vac pump. After having the unreliable 4X4 vac motor (CAD) fail on me and destroy the transfer case, I went with a Posi-Lok 4X4 system.

 

The switch is located on the T case, in the area of the front output shaft. It's a little awkward getting a wrench in there but it can be done. My switch had seized up on me because I somehow got moisture in the lines.

 

I can attest to the 4x4 posi-loks greatness as well. I went through 2 Vac CADs and 1 t-case switch before I went with the posi-lok...one of the Vac CADs that failed caused me to have to replace the inner passenger axle shaft and shift collar because it boogered the splines up. but hey, the vac CAD system works for some people, just not for me b/c my truck spent almost every weekend all weekend in 4wd.