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Old 04-19-2008, 10:10 PM   #1
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Thumbs up how to fix all vacume problems and how to locate the problems.

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.

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Old 04-19-2008, 10:19 PM   #2
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Old 04-20-2008, 12:25 AM   #3
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Consider it stuck.
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Old 05-15-2008, 04:03 PM   #4
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awesome good thread
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Old 06-19-2008, 02:46 PM   #5
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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).
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Old 09-04-2008, 10:28 PM   #6
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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!
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Old 12-13-2008, 10:13 PM   #7
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Hope these pics help.
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Old 12-13-2008, 10:17 PM   #8
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These pics are for the 94 2.5L.
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Old 12-13-2008, 10:19 PM   #9
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Last one.
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Old 01-05-2009, 10:37 PM   #10
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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?
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Old 01-12-2009, 07:21 AM   #11
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Where do the coloured vaccum pipes go?

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 ?
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Old 02-15-2009, 03:50 PM   #12
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Originally Posted by sxmjeepdriver View Post
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.
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Old 08-21-2009, 01:05 AM   #13
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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.
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Old 10-02-2009, 05:17 AM   #14
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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.
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Old 11-24-2009, 06:38 PM   #15
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This is a great post very helpful. Wish I would have seen it two weeks ago. I too after tracing the entire system bought the book, and Like Captcoop, replacing the TC switch was the answer.

I did find a new sealed tc vacuum switch on ebay for 7.95, the one at Advanced was 18.
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Old 01-20-2010, 07:42 AM   #16
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This is a very helpful post. Thanks. it helped me figure out why i had no front wheel pull
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Old 01-26-2010, 09:06 AM   #17
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...AWESOME....!!
thanks...
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Old 06-06-2010, 02:02 PM   #18
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Quote:
Originally Posted by rjkboyle View Post
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?
i always use brake dry or carb/choke brake dry doesnt leave oily residue for dirt to cling to
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Old 07-04-2010, 07:37 PM   #19
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DROX I,ve got an 88 the same. Lines were plugged off?? Seems to run better cooler than hotter ?? Its spaghetti but I,d like it where it needs to be
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Old 09-06-2010, 12:32 AM   #20
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Quote:
Originally Posted by rjkboyle View Post
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?
this works by temporarily sealing the vacuum leak, which evens out the idle for a moment.
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Old 10-05-2010, 09:37 PM   #21
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what i did witch i found a LOT easier was, i put the posi lock kit in it. i believe it was 120ish took 10 minutes to install and bypasses ALL that vaccuum stuff. a LOT easier.
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Old 12-08-2010, 11:59 AM   #22
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Good information. Well written too.
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Old 12-15-2010, 12:53 AM   #23
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Stupid question.. what does the vacuum do? Where is it located?
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Old 12-21-2010, 10:47 AM   #24
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where did you get the posi kit??
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Old 01-12-2011, 09:15 PM   #25
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i took all the vacuum lines off and flipped the shift fork housing upside down, bolted it back on and now its locked all the time like a tj. it works great. the front diff spins all the time but it doesnt affect anything unless there is another problem or you have a fulltime locker in front.
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Old 02-01-2011, 06:22 PM   #26
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I have a 91 YJ. Went through all the vac. check lists with flying colors. I pulled the actuator and watched it shift outside of the axle ok. If I manually slide the unit into 4X4 and put the actuator back it works untill I disengage it and try to reingage it, then no luck. My shift fork has about 3/8" of play between the fork and the shaft. Possibly this play won't let the actuator push the slide into 4X4? I ordered a fork from Quadratec to try a new one. Any suggestions would be appreciated.
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Old 02-04-2011, 10:22 AM   #27
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Google 4x4 posi-loc
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Old 02-04-2011, 12:50 PM   #28
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I replaced the 4WD Actuator. It worked once and shifted the Jeep into 4WH after a short turn of the wheel and a quick roll forward. It was working great. Then I backed the rear wheels into some snow and tried to use the front wheels to pull out. After a loud pop, the front wheels stopped working and rear wheels were spinning. The front wheels would not engage any more even after several tries. When I shift into 4WD there is a slight metal clicking noise like the front wheels are just missing engagement. Is there something I might have done wrong that is making the fork not slide all the way or anything else that would cause the system to slip out.
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Old 02-19-2011, 12:56 PM   #29
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wow this is well wrote thanks alot i am thinking i am having the same problems its not going into 4wheel all the way, the tire spins then kinda stops hope this is my problem i don't know what else it could be.
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Old 02-20-2011, 08:24 PM   #30
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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.

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