4x4 wont engage

there is a motor located on the transfer case check to make sure this is working

Are they vacum operated or you have to lock it in by hand? If you have an electric over vacuum control switch on the transfer case and 2 electric over vacuum switches, they are on the passenger side front fender well near the rear by the hood hinge, they are either green or blue and made of plastic, they both have vacuum lines and 2 wires connected to them. From there the vacuum lines run down near the front differential where they connect to a slave cylinder. the vacuum routes one way, the slave plunger moves and the differential engages 4WD, the vacuum routes the other way, the slave plunger moves again and the differential disengages 2WD (similar to a 90's model dodge 4x4).

Run this easy test. Label the vacuum lines that come from the top of the vacuum switches on the fender well (front, rear) use masking tape.

Start your truck. (make sure one of those switches has vacuum, put your finger over the nipples where you unplugged the lines, if you feel suction, you got vacuum) trade the vacuum lines, front to rear and rear to front. shift into 4x4, you wont get a 4x4 light, but if you now have 4WD then the problem is in the circuit somewhere between those 2 switches and the master switch on the T-case.

Keep us udated (remember to rate this).

There is a vacum actuator on the right side inner fender or under the battery box. Vacum line in one end, that operates a cable on the other end. This
cable engages and disengages the front axel.
Hope this helps.

There are three main things that could cause this. #1: in the passenger side kick panel is a module that controls the 4x4 and it should be clicking as you try to put it in 4x4.#2:There is a vacume activator switch on the transfer case located on the top on the drivers side.(If the module is clicking and trying to put it in 4x4 then I would just go to this activator switch).#3 If you replace the switch and it still dosn't go in to 4x4 there is a vacum diaphram under the battery tray that pulls the front end into 4x4.Check and make sure that there is vacum getting to the diaphram which is controled by the activator on the transfer case.If no vacume at the activator or diaphram check all the vacume hoses going into and out of the activator.If no vacume while vehicle is running suspect bad vacume line.You will need to remove the battery to test the diaphram under the battery tray.You will need to hook up some kind of battery to the cables with the battery out of the car to get it started in order to check for vacume at the diaphram.

first you need to figure out if 4 wheel drive in 4 low is working. i know you said it is but do the front tires actually pull... if it is than you have a transfer case issue... if it does not than you probably have a vacum issue with the front hubs

Any time your dealing with a 4x4 system the best start is at you front axle. Its primarily a vacuum leak so check to see if the 2 vac lines are hooked up (its good to check the electric connections.). When your 4 wheel drive is engaged and the motors running you should have vacuum at one or both of thee lines depending on if your in 4 hi or low .
If no vacuum at axle check the Vacum switchs(the plug with 4 vac lines) on top of the transfer case it will have 2 feed lines(grey & green) they conect in to the into the vacum harness on back of motor (passanger side). A vacum schematic is normally located on the raditor core support (right under the hood next to hood release)
Hope this helps

under battery is a vacum operated actuator that pulls your 4 wheel drive in to front axle.Make sure it has vacum going to it .Sometimes the actuator will get a hole in the rubber housing and 4 wheel will not engage.You could also check your vacum lines going to a canister on drivers side fender as sometimes the will come un-pluged and your actuator under battery will get novacum to it.If not it could be your actuator motor which is on the transfer case and is electric controlled and expencive300-400 dollars.Also could be a vacum line

you have a vacum leak in the 4x4 engagement system. there is a vacum solenoid on the passenger side next to the battery. should have 3 hoses to it I believe. check those hoses for cracks they go all the way to both front wheels. the ones in the wheel wells are usually messed up. if all hoses are good hook up a hand held vacum pump to each wheel they should hold about 15 hg on the vacum guage if not your wheel hub seals are leaking.

There is a vacum powered actuator on the front differential housing on the passenger side. It gets it's vacum from two valves mounted on the firewall just behind the battery(to left). The white line feeds manifold vacum to the valves. Check for vacum at white line with engine running. If no vacum there is a break in line from manifold. If vacum check the pink and blue lines by applying vacum to each one. The vacum should hold. If not check lines from valves to vacum actuator. Most likely it will be the actuator. If both lines hold vacum check valves. Remove electrical connectors from both valves. Connect a wire from one of the terminals of the valve to ground. Touch a wire from the battery + to the other terminal of the valve. Listen for a clicking sound. If no sound valve is bad. Replace valves(s). If this doesn't lead you to the trouble it's probably a mechanical problem inside the differential. However most likely there would other noises.

1998 dodge ram quad..front end wont lock in or the lights come on to tell you its in 4x4..***** little