1999 Dodge Ram • 316,000 miles

4wd shifter is fine; fr drive-shaft & diff engage correctly. Serious issues w/ front tires engaging. Problem seems difficult 2 narrow dwn. When 4wd light is on, fr tires biting/turning fine.

Fr axle Actuator solenoid has been replaced 2x (failed 18mo ago; ruptured diaphragm last wk). When pressure-testing vacuum lines, leak found n curator (ruptured diaphragm); hence 2nd replacement.

Upon shift n2 4wd, can sometimes feel fr tires trying 2 bite; but no 4wd light. Other times, fr tires & 4wd light don't engage @ all. After a few minutes r miles, 4wd light sometimes comes on & stays on. Sometimes it flickers back off. When shifting out of 4wd, sometimes light takes far 2 long 2 go out.

After shifting n2 4wd when going straight & slow, sometimes hear a low clunk and feel small pop thru gas pedal like fr axle trying to engage. Usually in this case, 4wd light isn't on. But sometimes, it flickers on/off.

After shifting n2 4wd when going straight & fast, may take 5-30 minutes for 4wd light to come on. Once it comes on, as long as I maintain speed (>45mph), 4wd light usually remains on; but will sometimes flicker off when slowing down (<35mph).

Bottom line, there seem 2b NO consistencies fr which to draw a solid conclusion. PLEASE HELP!
'99 2500 4x4 Sport QCSB loaded: 4.5" BDS Long-Arm kit, 35's, Road Armor bumpers, K&N Gen II FIPK w/ Amsoil filter, FASS Titanium 150, Mercury Marine injectors, TST PowerMax II, ATS Stage II trans, Banks wastegate, Banks turbo-back exhaust, SR removed
September 10, 2013.

I have to ask a couple questions so I know which system we are dealing with. Does the vacuum which goes to the actuator on the front axle first go through a switch on the transfer case? Do you manually shift into 4wd or is it an electric shift system? Have you checked vacuum to the actuator and is it steady? How many lbs of vacuum are you getting there?

Q1: Don't know for sure. Looks like it goes up into engine bay; but I haven't traced its origin. Working on more details for you.
Q2: Manual shift on the floor.
Q3: Vacuum lines checked and solid; will let you know lbs as soon as I get reply from Tech.

Is there any way you can obtain details via VIN or from Dodge OEM database based on my signature above?

Sep 10, 2013.
I don't have access to a database for Chrysler. I wish I did. Lol Let me know about the routing of the vacuum lines. On some transfer cases, the vacuum first goes through a switch which turns on the 4wd light and then the vacuum runs to the actuator on the front axle. I have see that switch go bad and not function properly. Thus, the 4wd would work then not work and the light would do what you described.

Let me know what you find as well as the amount of vacuum present at the actuator,


Thanks very much, Joe. That sounds like exactly what we're going to try & find out Fri morning (to include replacing the 4wd indicator switch on the Actuator itself). I can let you know tomorrow morning what the lbs of vacuum into the Actuator were. I sincerely appreciate your time & expertise.


Sep 10, 2013.
I just hope I can help. I'll look for your reply.


Morning Joe,

Looks like vacuum lines do indeed first go to the T-case. If it's a switch, I can't see it; but another SME thinks that T-case switch might be the problem. Still working on getting exact Actuator vacuum lbs measurement for you; usually 10-20lbs, but we'll see.


Sep 11, 2013.
The switch on the transfer case is my concern. Let me know what they find. If looking up from the rear of the t-case, it should be on the top right side. I have a feeling that is the problem, but see what they say.