How do i engage my four wheel drive in my 1990 yj wrangler?

Answer 1

The 1990 Jeep Wrangler came with an NP231 transfer case. To engage, put car in neutral (park also I believe will work if automatic). then firmly pull the short lever on the floor back till it stops. This should move the transfer case into 4X4. It then has a funky vacuum system that is "supposed" to engage the front axle The front axle is in 3 pieces. The outer passenger side is not engaged until the vacuum motor moves a sleeve between the center & outer passenger axles The 4WD lite should then light. Usually that vacuum operated motor freezes up or just falls apart with rust. It can easily be replaced, but many people choose to replace it with a manual cable operated system. Posi-Lok makes a nice one for around $200, or one can be made from common parts for about $25-30. Search the internet for articles that show how one can be made. Another option is if the motor is just frozen, take it off and soak it with PB Blaster or another good penetrating oil to loosen it then work it back & forth until it moves by itself. To do this, jack just the passenger side of the axle up as far as you can without taking the driver's wheel up. Be prepared to catch a small amount of stinky gear oil that is in the axle I have had to do this 2X so far recently because my 4WD is not used much where I live. Once I had it working good the 2nd time, I always engage the 4WD every time I start the Jeep. This keeps it moving and does not allow it to freeze up.