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Unread 02-06-2006, 08:55 PM   #1
dominiakrulz
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Join Date: Jan 2006
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4 wheel drive

hey guys, finally had an excuse to try the 4 wheel drive on my 91 wrangler that i just bought.... sad thing is it seems to kick on and off, didn't think anything to serious of it, until it just turned off for good. i have very little knowledge of 4 wheel drive. all help would greatly be appriciated

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Unread 02-06-2006, 08:59 PM   #2
cjb7804
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Check for vaccum leaks/loose connectoins going to the vaccum motor on the right side of the front axle. The lines run from the engine compartment to a switch on the transfer case, and back up to the axle. Check out all those lines and you'll prob. find something messed up there.
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Unread 02-06-2006, 10:10 PM   #3
paintguy
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the main vacuum comes from the intake manifold somewhere around the throttle body area and goes to a T over by the battery and then down to the front axel on the passenger side -- the vacuum line(s) does go back to the t-case after that, but I have found the problem usually lies w/in the engine compartment near or under the battery.
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Unread 02-06-2006, 10:33 PM   #4
Fenix85182
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Quote:
Originally Posted by dominiakrulz
hey guys, finally had an excuse to try the 4 wheel drive on my 91 wrangler that i just bought.... sad thing is it seems to kick on and off, didn't think anything to serious of it, until it just turned off for good. i have very little knowledge of 4 wheel drive. all help would greatly be appriciated
By the 4 wheel drive 'kicking on and off'... do you mean the light indicator on your dash? If so then that's a pretty clear sign that it's the vaccuum lines. The 4WD light is hooked into the same lines that lock your front axle, so if the light isn't coming on, the axle isn't locked.
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Unread 02-07-2006, 02:00 AM   #5
garin3
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Hey Brian, check them vacuum lines! Still waiting for that glove box, visors and wheel, too.
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Unread 02-07-2006, 11:25 AM   #6
ImRaptor
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The slider can shift over far enough to make to 4x4 light come on, but not far enough to engage the collar around the axel to actually lock in the front axel. That was my problem for a bit as the 4x4 light was coming on, which meant the fork was moving, but I was definetly wasn't getting any 4x4.
Turns out it was the shift fork that was the problem. The bottom of it was cracked and so it wasn't sitting on the shaft properly and was actually tilting backwards preventing hte collar from moving far enough.
This is particular to the 91's in mycase as they use an electrical switch for the 4x4 light, and not a vacume check switch.
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Unread 02-07-2006, 11:26 PM   #7
starblazer
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1991 YJ Wrangler 
 
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Below is a step by step to assist you in diagnosing your problem. Some Jeep owners have gone over to the 4x4 Posi-Trak system vs the OEM. The 4x4 Posi-Lok is a cable activated engagement device designed to replace the OEM vacuum and electric front axle engagement systems.

4x4 Posi-Lok is not a posi-trac or locker.
This applies to the following:
1987-1995 Wrangler YJ
1984-1991 Cherokee XJ
1986-1991 Comanche MJ
Note: With Dana 30 Central Axle Disconnect

Many Jeep owners comment that their 4-wheel drive is slow to or does not engage when the transfer case is
shifted into 4-wheel drive.

Function
The OEM front axle actuator is vacuum controlled. When the transfer case is placed in 4-wheel drive, the
vacuum plunger activates and pushes the shift fork, sliding the collar and coupling the freewheeling passenger
side (right) axle to the driven intermediate axle.

Cause
The vacuum system at times does not produce enough vacuum to engage the freewheeling right front axle to
the driven intermediate axle. If the vacuum actuator is malfunctioning, possible axle spline, shift fork, or collar
damage has occurred. See section 3.

Correction
1. Start the engine. Check for presence of vacuum at the intake manifold port that supplies vacuum to the
actuator diaphragm. If vacuum is present with the engine running, proceed to step 2. If vacuum is not
present, there are mechanical problems that need
to be addressed before continuing.
2. Check for presence of vacuum at actuator diaphragm
located on the axle tube
The vacuum actuator is located on the passenger side
(right) of the front axle tube. If vacuum is present
proceed to step 4. If vacuum is not present
proceed to step 3.
3. Check for hard, cracked or missing vacuum lines.
Replace vacuum lines as needed. Start engine
and place transfer case in 4-wheel drive. Check
for vacuum at actuator diaphragm. If the passenger
(right) axle still does not engage, proceed to
step 4.
4. Check the diaphragm on the vacuum actuator. If it
appears to be frozen or not working correctly,
replace with one of the following:
OEM Vacuum Actuator P/N 8353113
OR 4x4 Posi-Lok P/N PSL 900
Note: Before replacing the vacuum actuator, check
the shift fork for damage. See section 3-1.

Lack of vacuum, failing diaphragm or actuator (see
section 1), worn or broken fork, or burred
axle splines or shift collar (see section 3), may be


1987-1995 Wrangler YJ
1984-1991 Cherokee XJ
1986-1991 Comanche MJ
Note: With Dana 30 Central Axle Disconnect

Wear Pads
factors in partial engagement or disengagement.
1. Unbolt the actuator housing from the
axle tube by removing the four (4)
bolts. Inspect the fork for
damage or wear. If there is
excessive clearance between the
fork and the actuator shaft, the fork should be replaced with OEM P/N 5252599. Inspect the wear pads
on the tips of the fork for wear. If the pads are worn, replace them with OEM P/N 4137731.
Note: strongly recommend replacement of the aluminum fork with a cast iron fork P/N
4137727.
2. Slide the collar side to side over the axle splines to confirm free movement. (You may have to
rotate one axle slightly for spline alignment.) If it does not slide freely, it is possible that there is damage
or burrs on the collar and/or axles. The collar can be replaced with OEM P/N 4778548. For axle part
numbers, contact your local Jeep dealer.
Note: If a failing actuator has caused spline damage, the axle(s) and shift collar must be replaced before the
new actuator or 4x4 Posi-Lok is installed.

The parts referring to Posi-Lok part numbers is:
http://4x4posi-lok.ca/default.cfm#jeep

How the Posi-Lok system works:
The failure prone vacuum actuator is replaced with
the cable operated 4x4 Posi-Lok system. The
vacuum actuator is removed from the axle tube and
the 4x4 Posi-Lok assembly is attached and the cable
routed to a convenient location under the dash.
Engaging the transfer case and pulling the Posi-Lok
T-handle will slide the shift fork and collar to connect
the freewheeling right axle to the driven intermediate
axle. Both front wheels are now engaged and
pulling the vehicle. 4x4 Posi-Lok can be easily
installed in one to two hours with basic hand tools
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Unread 02-08-2006, 04:09 PM   #8
dominiakrulz
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wow thank you guys for all your imput, after reading this all, it sounds like it must be the vaccuum lines, becasue the light and the wheel will go on and off. Thank you guy, ill let you guys know the results of my fix when i get aroudn to it this weekend.
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Unread 02-08-2006, 04:25 PM   #9
89_Sahara
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Location: Baltimore, Maryland
Posts: 294
My 4WD works but my 4WD light never has. I replaced the bulb, but that wasn't the problem.
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Unread 02-08-2006, 08:01 PM   #10
jwrangler91
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Location: Fleetwood, PA
Posts: 130
i actually have a 91, and have the same problem
i just skipped the vaccum hoses and put in a cable to do it
but it still doesnt really work right
if you find out anything let me know, we probably have the same problem
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Unread 02-09-2006, 01:41 PM   #11
dominiakrulz
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well today i was able to take a look at it on a lift. I stimulated vaccuum to the actuator(sp?) to see if it was the vaccuum lines. nothing happened. i then noticed that one of teh vaccuum lines had been cut and blocked off with a golf tee. does anyone know the vaccuum diagram for this, and why this could have been done. the transfer case spins and no front wheels spin. my other thought is maybe the wires going down to the actuator are bad. does anyone know more information on what else could be the problem. thanks a lot.!

-brian
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Unread 02-09-2006, 03:28 PM   #12
MaineYJ
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there's a vac diagram and write-up in the FAQs at the top of this forum.
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Unread 02-20-2006, 01:04 PM   #13
dominiakrulz
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hey guys i still have had no luck with my problem... heres what i did so far

so i took the actuator from my parts jeep and made it into a posi-lock. Seemed like it worked so i put it onto my jeep. after taking out the non-modified actuator i noticed there were no wear pads on it. i installed my homemade posi-lock. I then went to try it out, i got no wheel hop on turns so i then put it up on jacks, and still no front wheels turned. I then tried putting the old actuator on it( i tested it and the fork moves when i suck on the hose), but this time instead of connection it to the engine vaccuum lines, i just feed a vaccuum line into the cabin(for me to suck on) to see if that engaged the front wheels. Still nothing happend. All i noticed now was that if i blow in the vaccuum line the 4wd light turns on, but its not actually functioning.

any other ideas guys?

thanks
-Brian
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