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Unread 12-27-2010, 06:53 AM   #1
JOExFROMxNY
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1988 YJ Wrangler 
 
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Location: Long Island, NY
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which nipple on axle vacuum motor to apply vacuum for 4WD

can anyone advise which nipple (black, yellow, or green below) on the axle vacuum motor needs vacuum applied to get the front axle to be engaged?



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Unread 12-27-2010, 07:02 AM   #2
kloppk
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The "Yellow" one. I believe it's the middle nipple.
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Unread 12-27-2010, 07:06 AM   #3
JOExFROMxNY
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can i just apply vacuum once to move it or does it need constant vacuum to stay engaged while running?
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Unread 12-27-2010, 07:11 AM   #4
Mark05059
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to stay engaged it needs vac all the time while running or it will slide back
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Unread 12-27-2010, 07:15 AM   #5
boydster00
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See the yellow that goes to the 4WD light switch? It needs constant vac to keep the switch engaged and to hold the fork in place. Lack of vac won't make it move back to 2, but it could move to 2 on its own. If you're trying to just get it working (as a temp fix), disconnect the red vac line from the engine vac system and run a vac line from the eng system down to the vac motor where the yellow line attaches. Disconnect the other lines. Your 4WD light wont work, but that should move and hold it in axle lock until you can get it working right.
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Unread 12-27-2010, 12:09 PM   #6
JOExFROMxNY
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Thanks man, it worked. I got 10 feet of washer fluid line and ran it from the red vacuum line to the middle nipple on the axle vacuum motor. Everything good now.You Brothers on jeepforum are the greatest help. once again you guys saved my day. that is why i always am a supporter of this board. Instant help. when you need it.
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Unread 12-27-2010, 02:52 PM   #7
boydster00
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Bravo, man. Now you can remove that whole 4x4 vac harness (yes, it all comes out in 1 harness without affecting anything on the engine) and take your time getting it fixed up.

One thing I found besides plastic lines that looked like they had been chewed on by mice was the blue relief / check valve. Mine was plugged. It's designed to relieve vac to atmosphere when changing from 4 to 2 and back, allowing the vac motor to move without vac on the opposite side of the diaphragm. It should draw air in in one direction, but should not allow air flow the other way.
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Unread 12-31-2010, 05:37 PM   #8
JOExFROMxNY
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Here are a couple of shots of what I did on my '88 to get it going in 4WD. I pulled the cone shaped thing from the hard red plastic vacuum line near the dist. cover and oil dipstick and connected an end of the washer fluid line i bought to it. It just slipped over it nice and snug since the red plastic was rigid. I connected the other end to the middle nipple on the vacuum shifter motor on the axle. The whole job took less than a minute and it worked great all week. Thanks again to all who suggested this quick fix.




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