Question about 1991 Jeep Wrangler

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Four wheel drive 91 wrangler

My four wheel drive will shift in and out fine but the light will not come on. ifound the two vacuum lines to the actuator were cut so i replaced them and it still didnt work. i thought they might have been crossed so i swapped them and my 4wd light came on but the shifter was in 2 and all four wheels were engaged. i had to swap them back two get it to go back in 2

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Check the wires on the transfer case mine got melted by my exhaust somehow and i just have learned to deal with it lol.

Posted on Jul 25, 2008

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I have a 91 jeep wrangler the 4 wheel drive stop working iv check the vacume hoses and they r good iv trace them bact to transfurcase to the front intake iv got vacume to the hoses by the batter but none...

first off what does that mean? 91 command trac system.
1: light dead in dash. ( means squat)
2: shift lever will not move. (i guess its ok)
3: tires actually do not turn on 4 ends of axles. (guess fails)

we cant guess, what tests fail, you must say.
do you have drive on the front prop shaft,
from transfer case to the front axle.?
91 books are hard to find, but does cover it.
ever read the FSM or its there.
my guess is you are saying the shift motor is dead/. that it?

25543740-y0lpcx5ujcsqxilomiw3wt0j-2-0.jpg if yes, did you do the steps in the FSM book yet>? read it?

  1. Raise and support the vehicle safely.
  2. Disconnect the vacuum harness and connect a hand vacuum pump to the front port. Apply 15 in. Hg (381mm Hg) of vacuum to the front port and rotate the right front wheel to fully disengage axle shafts.
  3. The shift motor should maintain the vacuum applied to the front port for a minimum of 30 seconds. If the motor does not maintain the vacuum, replace it. If the motor does maintain vacuum go to Step 4.
  4. Connect the vacuum pump to the rear port. Cap the port for the indicator lamp switch and apply 15 in. Hg (381mm Hg).
  5. The shift motor should maintain the vacuum applied to the rear port for a minimum of 30 seconds. If the motor does not maintain the vacuum, replace it. If the motor does maintain vacuum go to Step 6.
  6. Remove the cap from the port for the indicator lamp switch and determine if vacuum is present. If present, the shift motor is functioning properly. If not, proceed to Step 7.
  7. Apply 15 in. Hg (381mm Hg) of vacuum to the shift motor rear port. Rotate the right front wheel to engage the axle shafts. The axles must be completely engaged!
  8. Determine if vacuum is present at the port for the indicator lamp switch. If present, the shift motor is functioning properly. If not, replace the shift motor.
85357331.gif tests: this is just a vacuum servo , called a motor by jeep, its not a motor of any kind its a vacuum servo actuator.
it can be removed and bench tested, easy. just like all servos


Mar 09, 2015 | Jeep Cars & Trucks

1 Answer

My 2003 F-150 will not engage the 4-wheel drive when the switch is turned on? Two days ago it worked fine and the light does come on?

Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
If it turns it is a problem with the transfer case.
If it doesn't it is a front axle engagement problem.

I am going to guess the drive shaft will not turn, and the problem is the shift disconnect motor on the front axle, or the shift solenoids.
The shift motor looks like this

The shift solenoids look like this :

You can check the shift solenoids with a vacuum gauge. The blue vacuum line is the 4WD operation, the pink is the 2WD operation. Pull the vacuum line at the shift disconnect motor, and install the vacuum gauge. Shift into 4WD and the vacuum should be on the line, and hold. If not could be the disconnect motor or the vacuum line to the motor.

Could also be the shift motor in the transfer case, but with the 4x4 light on the cluster lighting up, the transfer case should have shifted, the confirm comes from the transfer case to illuminate the 4x4 indicator on the cluster.

Feb 20, 2010 | 2003 Ford F150 Regular Cab

1 Answer

I have a 1987 jeep wrangler and it will not shift into 4 wheel dr

The front axle connects 4wd by vacuum. check the vacuum hoses that run to the actuator. Pay close attention to the vacuum hoses running underneath the battery as battery acid can eat thru those hose easily. Good Luck.

Dec 27, 2009 | 1987 Jeep Wrangler

2 Answers

1991 jeep wrangler gets stuk in 4 low cant get out?

Hi fernandez,

Without knowing more, I can't really pinpoint the cause. But I can suggest some solutions.

On my '91, the hubs have a manual lock. I'm assuming if it in four-low the hubs were locked. Shifting the transfer case and even unlocking the hubs can be problematic on pavement.

Here's why:
With the hubs locked, the entire drive train is locked.

When you go in a straight line, no problem.

If you turn, the wheels on one side travel a different distance than those on the other side. But with the drive train locked, all the wheels are trying to spin at the same rate.

No problem if you're off-road or on slippery pavement. The wheels can spin a bit.

If you're on dry pavement, there can be a problem. There is a lot of stress on the system, especially the steering knuckles, and U-Joints. You need to relieve this pressure.

Drive it to a place (the side of the road works) with sand or gravel, drive it in a straight line a few yards back and forth. Put it in neutral while you are still rolling and shift the transfer case. Then unlock the hubs.

Hope this helps

Aug 13, 2009 | 1991 Jeep Wrangler

2 Answers

4 wheel drive doesnt work.

Has this Jeep been modified at all?
It sounds like the shifter cable was reinstalled backwards.
Specifically the 4-Low "Not Climbing Well". 4-Low should give you the best torque and hill climbing ability.
Do you feel any "Binding" in the steering wheel (difficult to turn)?
Remember a Jeep uses real driveshafts and differentials to give you 4WD - you cannot engage 4WD or 4-Low on dry hard surfaces. It needs a little bit of slip between the wheels for turns.
Check you're fluids too.

Jul 11, 2009 | 1992 Jeep Wrangler

1 Answer

1992 Jeep 4 wheel drive vacuum line for front axle

there is a vacuum switch on top of the transfer case it applies vacuum when the truck is shifted in to 4 wheel drive . if you connect it to direct vacuum you front axle will be engaged all the time

Jun 12, 2009 | 1992 Jeep Wrangler

1 Answer

Jeep Wrangler 1998 Sport Four Wheel Drive stuck in high

Try putting the car in neutral first. Try going in reverse while shifting out of 4wd.

Mar 10, 2009 | 1987 Jeep Wrangler

1 Answer

1987 Jeep YJ [Wrangler] so owner ship says''

Our Jeep Wrangler YJ's are equipped with a vacuum module on the front axle. It is used to engage the front axle when the transfercase is shifted into 4WD. Check the vacuum lines on the front axle to make sure they are connected. The passenger side axle shaft has a disconnect sleeve that is moved left and right by the vacuum.

Mar 01, 2009 | 1987 Jeep Wrangler

1 Answer

When i shift in 4x4 , the light goes on but i don`t have front wheel spin?

You would have to remove the vacuum lines off the motor and see if you got vacuum.

Oct 04, 2008 | 1991 Jeep Wrangler

4 Answers

2001 Chevy Blazer 4 wheel drive

The four wheel drive systems in these vehicles are simple. The push button controls the four wheel drive computer. The computer tells the encoder motor (on transfer case) to shift. When the transfer case shifts there is a vaccum switch on the transfer that is activated which sends vaccum to the accuator under the battery. The accuator pulls a cable to lock the front axle in. This covers all s series trucks and suv's with push button four wheel drive but not with auto or all wheel. Now to answer some questions. If your push button is lit up but will not go in to four high you should try to reset the four wheel drive computer. To reset pull the courtesy light and atc fuses for sixty seconds install fuses then cycle key on and off 5 times. If your transfer case shifts but your front end does not lock in check for vaccum at the switch on the transfer case in and out. If no vaccum out replace switch motormite number 49315 at parts store. If you have vaccum out check accuator.

Jun 02, 2008 | 2001 Chevrolet Blazer

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