Got my first Jeep. 4WD doesn't work.

[darkglass]

Hi Everyone.

I have a 1987 YJ 4.2L 5Spd. I've owned it for about 2 months. Wanted to try out the 4WD during this last snow storm and found that my front tires don't spin.

The 4WD drive light goes on when I put it into 4Hi and 4Lo. I've read some stuff about vacuum line being a common problem for this, but if my vacuum lines where bad would the 4WD light still come on?

Any help would be appreciated.

 

[SteelHeadz]

The 4wd switch is actuated thru the t.case shift rod by means of a Detent,so the lamp will turn on electronically but not necessarilly mean that your 4wd is actually working. The Engine vacuum is what's needed to actuate the front axle vacuum actuator to move a fork with a locking ring sleeve to the axle shafts
, thus enabling the axle to engage. the common cause of failure to this setup is a broken vacuum line on the passenger side below the battery tray. they are identified thru colors, so if you find multiple broken lines , just match the colors and repair them with a vac. hose that would slip snugly on both ends.

 

[Bounty__Hunter]

The 4wd switch is actuated thru the t.case shift rod by means of a Detent,so the lamp will turn on electronically but not necessarilly mean that your 4wd is actually working.

The 4wd light on early YJ's such as yours is activated by vacuum to the 4wd lamp switch mounted to the firewall. (The above mentioned activation is only on TJ's and newer XJ's).

Follow the vacuum lines to the front axle, there you will find the front axle disconnect. It's easy to remove the disconnect with the 4 bolts (a slight amount of gear oil will leak out). Once removed, move the shift fork back and forth by hand to check for smooth operation. If it moves smoothly, the problem is likely bad vacuum lines or a bad vacuum switch on the transfer case.

A method for testing the vacuum: Remove the 2 vacuum lines at the front axle disconnect. With the jeep running and tires chocked, have a friend shift from 2wd to 4wd and back while you feel for vacuum in each line. The vacuum should be strong in one line for 2wd and strong in the other for 4wd. This will help you narrow down a vacuum problem.