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Need 1989 YJ Wrangler Front Axle Vacuum Shift Motor Information

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New 1989 owner
I just picked up a 89 wranglericon1.png and it looks like its going to be a project. I have some questions so I looked thru the fourm but I am not understanding this thing.
1. 4wdicon1.png light is on and stuck in 4wd. Looking thru vacuum lines there is a blue line coming from transfer case forward but not hooked up. Where does that go?
2. on the transfer case i see 4l and N and 4h and 2h. fron the N position I only feel 1 gearicon1.png and that keeps me in 4wd. Am I missing something?
3. what is the proper way to activate the switch between 2wd and 4wd?
4. also has a really ruff idle......

ok thats enough for now...... any help would be appreciated.....

Joe

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Welcome to the forums, Joe!  

 

Regarding your YJ Wrangler transfer case, the shift lever moves the shift positions within the transfer case, this is not vacuum actuated. The vacuum is to the front axle disconnect mechanism.  This shift mechanism splits the right side axle shaft power flow when the transfer case is in 2WD mode.  Simply put, by splitting (disconnecting) power flow through the right front axle shaft, drag is reduced at the front axle and driveline.  The right side axle shaft is a two-piece design, split at the vacuum shift motor.

 

So, you do need the front axle disconnect mechanism to work for 2WD and 4WD modes.  There's a shift fork and vacuum motor assembly mounted on the front axle (right side).  Check the shifter and vacuum with a hand vacuum pump to make sure the mechanism works.  Then check/route the vacuum hoses from the transfer case to the vacuum disconnect motor. 

 

Make sure that vacuum applies to the front axle vacuum motor in the different transfer case shift positions.  Here are details on the front axle shift motor mechanism plus a vacuum diagram for the transfer case and front axle disconnect.  You can trace hoses and also test the vacuum switch at the transfer case.  You'll see the relationship with the 4WD indicator lamp, too.  Pay close attention to the Command-Trac illustration.  Your YJ is a Model 81 for identification purposes:

 

YJ Wrangler Axle Disconnect Motor Vacuum Lines.pdf

 

 

 

Looking forward to your participation at the forums!

 

Moses

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Thanks, I did but the books and see that section.  Is there a different position for 2wd H and 4wd H?  from N i only feel 1 position on the transfer case switch.

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Yes, Joe, there are unique positions for 2WD H and 4WD H.  You should have the NP231 transfer case.  (See I.D. tag at the backside of the transfer case.)  The shift lever pattern is: 1) all the way forward is 2H, 2) first pull back is 4H, 3) then Neutral and 4) 4L is at the rearmost position. 

 

Just forward of Neutral is 4H.  If you're having difficulty finding 2WD H, there could be an obstruction to the lever.  Make sure that the boot, carpet or floor pan is not preventing the lever from moving all the way forward to 2WD H range.  The shift to 2WD H is generally quite easy, this is a "Shift on the Fly" transfer case between 2WD H and 4WD H, although I like to let up on the throttle momentarily when I make this shift to take the load off mechanisms.  Shifting to 4L requires stopping the vehicle to prevent gear clash in the transfer case.

 

Moses

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Generally not, Joe.  Later vehicles simply eliminate the front axle shift motor and the disconnect.  Both sides of the front axle have solid axle shafts.  That said, the NP231 should allow shifting to 2WD readily.  If binding, try gently rocking the vehicle forward and back while exerting forward pressure on the TC shift lever.

 

There could be binding within the TC, though I would surely look for shift linkage troubles before rebuilding the transfer case.  We'll work through this...

 

Moses

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You narrowed this down to the vacuum shift mechanism and vacuum motor?  Trust your troubleshooting pans out, please keep us posted!  Replace any weak or embrittled vacuum hose.

 

Moses

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New cad installed Tc does shift better but 4wd light on. Vacuum only on yello hose. Not black no matter what I put the shifter in. Any ideas????

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Good job and diagnostics, you nailed the shift motor issue! 

 

Check the vacuum at the transfer case switch.  Check port to port at the switch with the transfer case shifter in different positions.  If the switch is defective or leaking off, you would not have vacuum on a circuit.  Make sure the vacuum source line from the engine manifold is in good shape and that the check valves are okay, too!  The check valves are essential and cheap to replace.  They are noted in the vacuum diagram PDF above.  You can test one-way check valves and the vacuum switch with an inexpensive vacuum hand pump/gauge.

 

Moses

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