Part Time Light?

I recently picked up an 88' 4.0, 2-door, auto, NP 231, XJ over the past weekend. It is in very excellant condition considering that it has 178,000 on it.

The problem is that the four wheel part time light on the dash is always on, no matter what position the transfer case is in, it even is on in neutral. I can tell by driving it that when the transfer case is in two wheel drive, it is actually in two wheel drive. This light apparently isn't triggered by the transfer case.

This leads me to believe that it is actuated by the vacuum front end. Can this light be accurately used to tell me that my frontend is locked in? I ask because I have heard horror stories about Jeep's vacuum disconnects. If my frontend is indeed always locked in, is there any problem driving it around like this on the road? The frontend obviously wasn't designed to constantly be turning, if it was then the vacuum disconnect wouldn't be there, but will driving it like this wear out U-joints or any other parts?

Also, a couple of days ago I was heading up my driveway and it started to spin in two wheel drive. I stopped and shifted into four wheel. I released the brake and the rear tires continued to spin and there was what sounded to be a quiet "clicking" from the frontend/transfer case area. It sped up as the rear tires sped up. I then shifted into four low, and it went into four wheel low and I continued up the driveway. This is the only time it hasn't gone into four wheel drive in the dozen or so times I have used it so far, is it anything to worry about? An omen about future breakage? Or did I just not pull the lever far enough or something?

I had a similar problem recently. I would guess that your axles are not fully engaging, probably because of a vacuum problem. Your 88 has disco axles like my 91.

First thing you should check is that your vacuum hoses are properly attached to the "vacuum motor" which is a round disk shaped object attached to the fron axle. If they are and the axles are still not locking check to see that there is vacuum present in the line up to the motor.

In my case there was vacuum up to the switch on the transfer case but not past that point.

There are several things you can do if the vacuum system is not working. In my case I could have replaced the faulty switch. It could be a cracked/broken vacuum line, that could be replaced. It could be that the vacuum motor is shot, it can be replaced.

Now in my situation I choose option X, which was to completely bypass the fragile, error prone vacuum system.

There are three ways I know of to do this.

1. Buy a product called Posi-lock which uses a cable to actuate the fork that makes the axles solid.

2. Make your own cable actuated setup.

3. Open up the cover remove the c-clips that hold the fork on. Then shim the fork into the locked position with washers, slide the collar over both axles and put the fork back on. This will keep the axle locked at all times, which is essence what Jeep ended up doing with the newer XJ's with solid axles anyways. I did this 5000+ miles ago and it has worked great. No more vacuum problems, everything works great and it only cost $1.75 to fix.

argalaviz said:

2. Make your own cable actuated setup.

Click to expand...

How do you do this. Do you have anypics or anything that could help me?

Thx Spc Stauffer US Army Iraq

Jeepin_rebel said:

How do you do this. Do you have anypics or anything that could help me?

Thx Spc Stauffer US Army Iraq

Click to expand...

This webpage explains it. Look for the link on custom made axle disconnect.

http://home.earthlink.net/~stevenschreiber/jeep/

Thanks to Steven Schreiber for the write up.

argalaviz said:

This webpage explains it. Look for the link on custom made axle disconnect.

http://home.earthlink.net/~stevenschreiber/jeep/

Thanks to Steven Schreiber for the write up.

Click to expand...

That's a pretty clever design. I tried a similar setup a few years ago, using the cable to pull on the metal plate of the diaphragm assembly, but the geometry wasn't right and cable routing was an issue. It was hard to get enough force on it. It hadn't occurred to me to shoot directly for the fork.

Jeepin_rebel said:

How do you do this. Do you have anypics or anything that could help me?

Click to expand...

I got this off the internet, and although it's not my design I have it posted on my web server (IIRC the other fellow's server was his home computer, so wasn't available all the time). When I first posted this I got his permission, so I have continued to display it. I haven't used it, but it seems pretty simple and straight forward.