Are you ready?? here it goes. tools needed: socket sets and ratchet, hand operated vacuum pump. and possibly some skinny rubber hose to sleeve broken vacuum lines. if any broken lines, cut and sleeve them duhh.

FRONT AXEL SHIFT MOTOR PROBLEMS CHECK: make sure to raise the front of the vehicle and support it securely on jackstands.
1.) Disconnect the vacuum line from the shift motor and connect a hand held vacuum pump to the front port of the motor.
2.) Apply vacuum to the motor and rotate the right front wheel to ensure that the axel is fully disengaged. The shift motor should hold vacuum for at least 30 seconds. if it leaks, REPLACE IT.
3.) if the motor holds vacuum connect the vacuum pump to the rear port on the shift motor. plug the other ports and apply vacuum once again. it should hold vacuum for 30 seconds also. if not replace the motor.
4.) With vacuum still applied, remove the plug from the port where the vacuum line to the transfer case connects. Check for vacuum. if vacuum is not present continue on to step 5. If you have done all vacuum checks, and have passed all, but still does not engage 4x4. shift to 4x4 and drive a few feet with friend to look under to check if shaft from front of transfer case is spinning to front axel. if is, hook vacuum pump to vacuum line coming out of switch located on firewall beside the battery. apply vacuum and go drive in circles and you will be abel to tell if it is in 4wheel drive. if it works then replace the vacuum switch located at the top of the transfer case. "it has four vacuum lines coming from it". its like $12 bucks and super easy to change. this should fix the problem. if not. on to step 5.
5.)Rotate front wheel to ensure that the axel has shifted completely. If it hasn't remove shift motor and check for freeness of the sliding shift collar.
6.) inspect the vacuum harness from the shift motor to the transfer case for kinks cracks and other sorts of damage. check the vacuum harness connectors for a good tight fit on the vacuum ports.
REMOVAL:
1.) unplug vacuum harness from the shift motor.
2.) remove shift motor housing bolts and lift shift motor housing, motor and fork from housing. also remove all traces of old gasket material.
3.) Mark the relationship of the shift fork to the housing to return it to its original position upon reassembly.
4.) Rotate shift motor and remove shift fork and motor retaining snap rings. by pushing them down with two screw drivers. pul the motor out of the housing.

I sure hope this helps all those poor soles like me for the past 3 weeks that have those sleep robbing vacuum problems. i bought the jeep book, which is where the steps came in and mine passed all the checks and the book does not mention anything about the vacuum switch located at the tp of the transfer case. thats what i replaced and thats what fixed mine. and all the parts that look improvised on step four was what i did to narrow it down. GOOD LUCK.

Cool. Sticky that.

Consider it stuck.

awesome good thread

I believe my vacuum harness connectors are completely torn in two on my front axle, and I was wondering what the effects of this will be? One was completely torn off right at the plug in point, and the other had a very small, threadlike, piece of wire still holding it in place until I bumped it and it completely snapped off.

(I was trying to figure out why my 90 Wrangler wasn't starting, so I was looking for the Starter/Solenoid to try bumping it with a hammer first to see if I couldn't try starting it).

A quick way to find vacuum leaks on something like that - blow smoke into the line - see where it comes out.

Good for troubleshooting heater controls too.

Caution - some devices have a small bleed valve or hole on them so they don't "trap" vacuum, so just seeing smoke come out doesn't always mean bad - but it's a good place to start!

Hope these pics help.

These pics are for the 94 2.5L.

Last one.

I heard somewhere that you can check to see if its a vacuum leak by doing the following.

Starting the jeep
and spraying the vacuum lines with WD40 and if the rpm rises a bit, its a vacuum leak.

I'm not to sure how reliable this is. I don't think it makes much sense, can anyone shed some light on this?

All i have is cap on the transfer case with about an inch of vaccum pipe of each colour. Does anyone know where to terminate each of the colours ?

I had posted that on here a few years ago. I'm not sure where, but you might can find it. I looked in my folders, but I no longer have the information saved.

I completely agree with you.You have done an great job.I appreciate the information you have laid out here.Thanks for forwarding this useful information.

I just bought my 89 YJ I have plug lines with flathead screws in them. I dont know where they go and or where the other part of the vacuum line is. My jeep runs but it got problems.