So I have been pretty happy with my truck and it's never let me down.. until last saturday.
I did notice that the 4x4 light sometimes didn't light up on the dash, however I always assumed it was still locking in becuse I never had any traction issues.

Anyway on saturday I did find some traction issues and found that the front isn't locking. This doesn't have locking hubs (which I am used to and I still think I prefer but that's another story for another day) and it's supposed to engage when you throw it into 4H or 4L.

Anyway I had to get pulled out and look like a moron and I'm not gonna have that happen again so I need to get this fixed. What should I start with checking and looking at?

I can see there is some deal with two vacuum lines going to the DS 1/2 shaft in the front and the vacuum lines appear to be OK, but can someone explain in laymans terms how the system works and what I need to be checking.

Is there a switch on the 4wd shifter that could be out of adjustment?

Anyway to easily test the front vacuum unit I mentioned above?

All help is greatly appreciated! I can't let this thing stay 2wd or I'll never hear the end from the Dodge diesel crews..

 

Check all the vacuum lines running down to the differential, to make sure their still in good conditon and not broken/cracked/disconnected. Then, look in the FSM for the procedure for checking the 4wd VSS switches mounted to the fender. I'm not sure on the procedure myself, but I know it isn't that hard.

-Edit-Here's a link for a little more help.

http://www.off-road.com/trucks-4x4/t...tem-19259.html

 

IIRC, the front axles are always spinning, even when in 2 wheel drive, thats why most replace the hubs with manual ones (asin or warn)

 

yes, the front axle's are always spinning, but I believe the issue he's having is that either that the ADD system isn't working. The actuator probably isn't moving, for one reason or another. When I worked at the dealership, we recommended that people engage 4wd at least once a month, to make sure the actuator's didnt freeze up. I've replaced quite a few on newer tacoma's and tundra's because of this.

 

X2

My 95 T did the same thing. Remove the wrapping on the lines and check em. When it happened to me, one of the lines melted on the exhaust manifold.

 

Interesting, my T sat for over two years (one year outside) while I put it back together after the roll over and I took it out two weeks ago, shifted into 4 wheel drive and it worked right away. Then I did some vigorous wheeling this past weekend with no problems at all!

 

Congrat's on gettin your truck back up and movin!

Ya, I've replaced many many actuators. Mostly on Tundra's, Tacoma's and 4Runners, but I have seen them freeze on the older ADD diff's like in our T's.

 

Hey, my 4wd does not engage from time to time in my 96 also. seems something heats up after a long drive, and the tranny/t-case/ whatever needs to cool down before it will. Had to pull mine off the beach once with a 4cyl nissan. embarassing. I'll leave it to better wrenches than I to decide what actually heats up, but if i let it sit for a while. or try the next day, it works fine. Good luck!

 

Not to Hi-jack this thread, but I have searched everywhere on a ton of forums and haven't found anybody that is describing the issue that I'm having. The issue: Just bought a 1997 T100 4x4, and the 4x4 doesn't engage. What happens when I shift into 4hi or 4lo: Light on the dashboard immediately lights up, I hear a clicking in the dash from the relay, and I hear a sort of wirring/rubbing sound coming from the tcase/diff area. I have checked all the vacuum lines, solenoids, etc. Vacuum is applied to the right lines at the right time, so I have ruled out the solenoids and possible vacuum issues.
With the front wheels jacked up in 2wd both wheels spin freely (not moving the others, like a 2wd truck.) When I shift into 4wd the wheels slightly turn each other but not locked in like they should be. I thought the ADD in these trucks meant the front axle was always locked, even in 2wd. But obviously I'm misinformed. Plz halp.

 

Probably because your post contains spam....

 

My 95 t100 has that same issue. My vacuum lines are good 👍 had them replaced. My 4wd light does not appear on the dash and my 4H and 4L don’t engage. Idk what to do 🤷🏻‍♂️