So, here's a little background information. I bought this truck about 6 wks ago, and at that time I had wild vents, weak cruise control, and the 4WD light took forever to turn off. After much searching, sweating and swearing, I found a damaged section of the metal line that feeds the red line that goes into the axle.

I repaired it by cutting out the damaged section with a dremel and patching it with some rubber tubing. All of those problems went away.

Today I was going down a gravel road, and put it in 4WD just for ****s. When I pulled it out again, the 4wd light turned off after about a mile... then came back on again. It won't turn off.

I went over all of the vacuum lines underneath a little while ago when I was changing the xfer case oil (very messy), found no new damage. I replaced the patch job with some heavier duty line but it made no difference.

I noticed that the black line has strong vacuum while the red has little to none. It was this way when the shift lever was in 4wd and 2wd. Is this normal? Is one a feed line and the other essentially a return line?

Also, there is an electrical connection onto a "bolt" on the axle. Is this just a sensor or is this the solenoid that controls the vacuum/axle? Is it possible that this is bad and, if it's a sensor, the axle is actually unlocking? Is there any point in pulling it out, and will oil come out if I try to pull it to inspect it?

Thanks for reading.

 

put it in reverse, drive backwards 10-20 feet, problem solved

 

I already tried that. It didn't work :P

Damn thing.

 

ok, here's how its all supposed to work.
http://www.dodgeram.org/tech/repair/..._engagment.htm
http://www.4x4wire.com/dodge/tech/solid_axle_cad/

to sum it up, you should have vac on one line in 2wd (to disengage the cad by moving shift fork to passenger side) and vac on the other in 4wd (to engage cad by moving shift fork towards drivers side). the vac switch is on top of the t-case. there is not a "return". it should be a vac on one or the other.

the wire and bolt looking thing is a switch that controls the 4wd indicator light on the dash. its easily replaceable from autozone for about $20 if necessary. its just a simple contact switch.

for testing and repairs, don't trust the light until you know for sure that its telling you the truth. its just as failure prone as the shift fork itself. put it up on 4 jack stands so you can crank the truck and shift and test.

after you fix it a couple of times, and get tired of screwing around with it, check out posi-lok. its a manual cable thats foolproof. about $200 or less. don't spend a lot of money replacing the cad. it can usually be repaired by cleaning it. and if you do decide to replace it, consider the posi-lok as a better alternative.
https://dodgeforum.com/forum/2nd-gen-ram-tech/95395-posi-lok-installed.html

 

Here's what I just did:

I pumped up the red line with a miti-vac and it holds vacuum. I then turned the key on and the 4wd light wasn't on... cool! I started the truck and I heard it click into place and the 4wd light came back on. I pulled the switch and tested it and it's fine.

I pulled the big rubber connector from the top of the xfer case and inspected all the lines-- they appear to be good. I checked the vacuum line on it (grey) and it was about 40lbs. I put the plug back on and pulled the black line from it and checked the spot on the plug where it connects-- vacuum from the switch. THis was in 2wd. It was the same in 4wd. THe red line never has vacuum to it.

So to me it seems to be the vacuum switch unless someone can think of another explanation.

What's involved in replacing it? Is it just threaded in and easily changeable, or does it involve dropping the xfer case?

At least it happened BEFORE I changed the fluid so I know it's not my fault :P

Thanks
Chris

 

Ah, I see in one of your links that I can just unscrew it and clean it. Cool. You've helped me a great deal, thanks a lot.

Chris

 

i don't see that t-case vac switch listed on autozone.
here's a site with some t-case info, but its a real pita site.
seach on this part number. it might/might not be right. idk. ALT15832 for NP-231
http://drivetrain.com/

 

Yeah, I broke one of the nipples off trying to break it loose. God dammit. I think I'll call around Monday to see about getting it replaced since I'm obviously incapable of doing it myself. :/

 

Does anyone know what size wrench I need for the vacuum switch? The largest I have is 22mm and that didn't cut it. I'd like to see if I can get the old one out (since I already broke it as it is), then put it back in to plug the hole, so I can just swap it quick when the new one shows up.

 

aw, that sucks. don't give up. how about a big pair of channel-locks ?
here's an old post with the same problem. like most, no wrapup post saying that it did/didn't fix it and no pics.
https://dodgeforum.com/forum/2nd-gen-ram-tech/157690-4wd-vacuum-problem-help.html