Cannot engage 4 wheel drive

[Derek Emblin]

I recently purchased an '89 Cherokee Laredo 4.0, and the seller told me he had only ever used the 4 wheel drive capability once in 8 years. First I saw the dash indicator light was not illuminating, and on inspection found that the vacuum hoses had parted from the vacuum pump on the front axle, easy fix thought I, especially as the dash light was now working. I was wrong, it was not engaging 4 wheel drive. I lifted the front end and removed the vacuum pump and the pipes that connect to it, there are three. I cleaned the pipes and checked the fork for damage. Next I checked the sliding collar and made sure it a) slid back and forth, and b) engaged and disengaged the front wheels, all good. Then before reassembling I connected the pump to the vacuum lines and made sure the pump was working by engaging and disengaging the transfer box lever, the fork moved back and forth perfectly, this with the engine running. Before refitting the pump I made sure that everything was syncronized, the sleeve and the fork were both in the 'engaged' position. With the front still off the ground I started the engine and went from 2x to 4x at least 6 times, each time checking that the wheels were either locked or free. One point here though, the dash light did not illuminate in 4x. I was not unduly worried as I was happy that the mechanics were working. I drove in 2x to a nearby area where I could test it. No go, I got stuck, no 4 wheel drive, even though by some miracle the dash light now worked. Once back on hard ground I jacked one front wheel off the ground and with the transfer lever in 4 high, the dash light lit, it was still in 2x . Now I'm totally confused, is there something I didn't do, or something I did that I shouldn't have? Help me Obe One, you are my only hope.

[AlohaBra]

Try look at this PDF:
http://www.lp2aenergy.com/PDF/88XJ/

[Derek Emblin]

Thanks a million for the info. I now need to find a vacuum tester, but I'm guessing it would be cheaper just to buy a new motor and be done with it, at least then I can eliminate the motor from the problem if it persists.

[Derek Emblin]

Its the command-trac system.

I'm having some difficulty locating where to reply to all the really helpful suggestions I've received, so I'm doing it here!
Guys thank you all very much for your input, it helped me tremendously, I now understand fully how the system operates, something that the workshop manual I purchased failed to do. What had be baffled was that I managed to get it to operate when not under load, so with the aid of the diagrams and hints I received I deduced that it was not getting sufficient vacuum to slide the collar, so starting from where I had stopped cleaning the pipes I began systematically to remove them and ensure they were clear, and lo and behold I found a blockage in one of the metal pipes, which made it extremely difficult to clear as they are bent every which way. Once cleaned and reassembled it worked like a charm and I was able to go and play in the deepest sand I could find without a hint of bogging down. Again, many thanks to everyone who came to my assistance, I really do appreciate your help. Derek

[AlohaBra]

I would recomend geting the vacuum pump and gage first (one unit)...it might be cheaper. You can use it later (remember...you own an XJ Jeep).

[Stick89]

Trace the vacumn lines from the x fer case ...the hard plastic lines deterioate really easy due to the heat in the engine compartment...make sure that ALL the vacumn lines are not broken ANYWHERE....Even if only 1 line is broken it will effect the whole vacumn systwm...start with the VACUMN CANNISTER...should be on the passenger side behind the bumper...IF there are cracks you might be able to fix them with some epoxy glue...IF the cannister is really FUBARED then you have no choice but to replace it....Lemmee see iffin I can find a diagram of the vac sys....

Found this....adjusting linkage ....scroll to your specific x fer case
https://www.autozone.com/servlet/UiB...3d801540ae.jsp

[Derek Emblin]

Oooops, now I find where to reply..............guys I've written quite a story further back. Thanks to all your help I now have a Jeep 4x4 that actually has 4x4. Thanks a million.
Derek

[AlohaBra]

Great, we love a success story especially a description so we can learn more of what goes wrong.

Aloha and best regards,