4WD inop... some help

Specs:
88 XJ
230K

Alright here is my problem: The 4wd is inoperative. When you put it in 4wd the light will sometimes come on, sometimes not but it is still inop. When i put it in 4low the gear reduction of the transfer case can be felt, therefore the t-case seems to be doing its job. Is my problem in the front diff? A fix? a better than oem fix? 4X4 posi lock???!!! any advice would help.

what front axle do you have? do you have the vac disconect dana 30?

xjwisconsin said:

what front axle do you have? do you have the vac disconect dana 30?

Click to expand...

it is a dana 30 and i believe it does operate on vac

If so here is a really quick and easy way to check some stuff out
1. block the rear wheels
2. take a jack and jack the front passenger side axle up so the tire spins free
3. Start vehicle and engage 4wd low or hi, doesnt matter
4. get out and try to turn the front drive shaft (cant turn it? good, transfer case properly engaged)
5. if Tcase working go the passenger front wheel. can you spin it? (if yes not good) means several things

try this out and see where the problem is at

that vacuum disconnect is what you'll have to start troubleshooting. A vacuum pump is very handy here.

First of all, you should check to see that the vacuum lines and the vacuum reservoir are not broken or leaking. The reservoir is located behind the bumper on the far right, and it can crack. If it's been bumped or dislodged, make sure that the mounting feet have not broken off, leaving holes.

You can take the vacuum disconnect motor off the axle, and test it in various ways for leakage. It's a simple diaphragm gadget, with three vacuum nipples on it. One of those is the tap for the vacuum operated indicator light. If you plug the outboard port with your finger, you should not be able to push the fork back and forth.

Check the fittings on the vacuum motor for leakage and softening. Also make sure there are not rust pinholes in the metal lines.

Finally, you may have to replace the vacuum switch in the transfer case. That, fortunately, is not too expensive.

When I had an 87 every single possible mode of failure in this system occurred at least once. Many people solve this problem the simple way by stacking washers on the shaft of the vacuum motor, to keep it permanently engaged. There's little penalty for doing this, except that you will have to rig some other way of operating the "4WD" indicator light.

Alright im gonna do some testing and inspect the vaccum system. besides the washer idea, is there any other strong fix for the vaccumm problem???

other than doing some type of posi lok type work I beleive switching in the passenger side axle shaft from a later non disco will be your only option.
as mathew said check the vac lines first... If you dont have a vac pump(i suggest getting one they only cost like 20-30 dollars) with the engine running pull the vac lines and see if you can hear them working there is a rubber plug thing that plugs into the vac motor on the axle and they wear out very easily. I just ditched mine and ran an inch and a half piece of rubber hose off each vac line to the nipples on the motor...
White-controls the light on the dash
green-connect
yellow-disconnect

You also might want to check the shift fork. I have seen them so wore out that they have an oval hole in them and the slop does not allow for full engagement into 4wd.