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Old 02-21-2010, 01:12 AM   #1
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Exclamation 4WD problem

i have an 89 yj and when i go to put it in 4WD it makes a sort of whining noise i guess like it's engaged but stays in 2WD... i dont know what it could be... Vacum motor? please help.

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Old 02-21-2010, 03:51 PM   #2
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anyone???

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Old 02-21-2010, 03:56 PM   #3
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Hey 89
do a search in the forum, look in the upper right corner, there has been many threads on this subject.
Do you know for a fact that the front axle isn't locking in?
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Old 02-21-2010, 04:03 PM   #4
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ya i tried it in the snow when it was really slippery and i'd put in 4WD and give it some gas and the rear tires would spin all day... and when i tried to drive it out of the snow bank from the plow trucks it would hit the snow and spin the rear tires. i tried 4LO and 4HiGH, and when u put it in 4LO it makes a sort of whining noise which sounds normal, but it stays in 2WD... its like driving a car...
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Old 02-21-2010, 04:07 PM   #5
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i was looking and maybe a vacum motor???
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Old 02-21-2010, 04:08 PM   #6
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Had the same problem with 4 wd on 88yj not engaging. Replaced all vacuum lines. There was sufficent information on this forum to aid me in correcting the problem.
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Old 02-21-2010, 04:09 PM   #7
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and replacing the lines fixed it?
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Old 02-21-2010, 04:20 PM   #8
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Just replaced lines. Lines were old, cracked, a couple missing. I am not real mechanically inclined but found protocols on here for testing vacuum activator or attenuator or whatever it is called on the front axle that engages the 4wd. I took the time to read all the posts on this issue, applied vacuum to the vacuum activator and it seemed to engage and just started working backward. There is a diagram of the vacuum circuit in one of the posts.

Went that route rather than the posi-lok cable. I might have been ahead of the process installing the posi-lok but I am trying to learn as much as I can by trying to do things the hard way.
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Old 02-21-2010, 04:38 PM   #9
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ok thankyou i'll read up on it some more.
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Old 02-21-2010, 06:02 PM   #10
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Here ya go, see if this helps

The vacuum lines for the 4wd axle disconnect system always seem to get unhooked, melted, or ripped totally off. Here is a way to check to see if everything is hooked up right, and if it isn't, how to hook it up the right way.

On top of your transfer case will be four nozzles that control your front disconnect system for your 4wheel drive.

The red line coming from your transfer case is the hose for the vacuum source(constant). That will hook up to a hose running behind your air cleaner, if it is still there. Take a look and you will probably find the remains or the original red line. If you don’t have the remains of the original line that is hooked to the constant vaccuum source, find a port on your intake manifold that has a constant vaccuum(or ports on your carb).

Take apart the plastic housing around the vacuum harness(don't break it) to see the lines. Connect what seems to match up for now. Your best bet is to cough up the $30 that a new vacuum harness costs at the dealer and install that instead of driving yourself insane with broken lines.


(blue line) Leave hanging, it has a check valve on it which gets hooked to nothing.
(red line) Hooks up to a good constant vacuum source off of the manifold.
(green line) goes to the shift motor on the front axle. Horizontal on the shift motor.
(black soft vacuum hose) goes to the plug on your firewall by the battery for the 4wd indicator on the dash.
(yellow line) goes straight to the shift motor; one of the lines that goes into a two line plug verticle on the shift motor.
(black hard line) goes with one of the yellows to the shift motor. Plug located vertically on top.
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Old 02-21-2010, 07:23 PM   #11
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Thankyou very much tht was a big help.
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Old 02-25-2010, 07:11 PM   #12
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same problem here, it changes without noise, and the rpms even change in 4W-Lo but only the back tires continue to spin, im looking into the vacuum cables and such, let me know about your progress.

it will sometimes engage, about once every 10 tries, leads me to believe something needs cleaning or lines need replacing
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Old 06-20-2010, 04:01 PM   #13
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This must be a common thing to have go wrong. I just bought my first Jeep 89 Wrangler, and I have the same thing. I can feel the transfer case sucking power from the engine but only the back tires spin. I hate chasing vacuum leaks!!
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Old 06-20-2010, 09:25 PM   #14
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just lock up the front axle like me and many others have done...
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Old 07-08-2010, 06:53 PM   #15
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Hello everyone- I'm Mike in NC, new to this forum. Same issue, rear tires spin and no front tire movement. The dash says I am engaged, but that is only a switch. I replaced the actuator already, does anyone know how much vacuum I should be drawing?
Thank you for any help you might have to offer.
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Old 03-09-2011, 04:46 PM   #16
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this has helped me out alot thanks for the thread man
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Old 03-09-2011, 04:51 PM   #17
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Blu I think part of it depends on which model year you have as to how the 4wd light and the actuator work.
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Old 03-09-2011, 07:49 PM   #18
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What can I do to get rid of the vac lines? And where do I get the replacements

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