4WD Vacuum problems - JeepForum.com
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post #1 of 2 Old 04-03-2010, 11:05 AM Thread Starter
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1995 YJ Wrangler 
Join Date: Jan 2008
Location: Raleigh, NC
Posts: 152
4WD Vacuum problems

So, my 4WD quit working this winter and I finally have the weather to look at it.

Front drive shaft turns.

While inspecting the vacuum on the shift motor connectors it appears that the vacuum is weak and also reversed. The FSM says that the line to the outboard connector should apply a vacuum when set to 4H and the inboard should apply a vacuum when st to 2H. Mine is the opposite.

The level of vacuum feels weak to me. The local auto parts store loans out a vacuum test kit so I'm going to pick that up and see what it says.

I'm wondering if this may point to the vacuum switch on the transfer case. Any ideas?


Pressure is OK. 15 HG, just what the FSM says it should be.

Last edited by denalione; 04-03-2010 at 11:40 AM.
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post #2 of 2 Old 04-03-2010, 12:57 PM Thread Starter
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1995 YJ Wrangler 
Join Date: Jan 2008
Location: Raleigh, NC
Posts: 152

Even though i was very careful to not swap the two vacuum lines to the shift motor I must have done so. Will someone please verify that the outboard vacuum connection is activated when set to 4H and the inside when set to 2H?

Since I could consistently see one of the lines measure -15 In HG when in 4H I attached this one to the outboard port. Even with this set and the front drive shaft turning the front axle still was not going to drive mode. I'm thinking the shift motor needs replacing.

Any body got any opinions on this? Yes? No? I'm an idiot?
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