2wd to 4wd 1988

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1988SCWaggy
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Joined: Fri Dec 17, 2021 5:22 pm

2wd to 4wd 1988

Post by 1988SCWaggy »

What is the exact process of shifting from 2wd to 4wd? My 1988 GW has the 2wd to 4wd switch, I move it from 2wd o 4wd and hear the vacuum hiss, but 4wd light doesn't come on. Does transmission need to be in neutral? What is proper step by step process? How can I confirm its in 4wd?
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Stuka
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Re: 2wd to 4wd 1988

Post by Stuka »

For going from 2hi to 4hi, it should just work. You can shift while driving down the highway.

Its possible its just something with the light, the wiring, or the sensor which is causing it to not light up. You can trouble shoot that using a multi-meter.

EDIT: Before doing what I posted below, verify that the lever actually moves as posts below mine stated. I skipped this step in my initial response.

Your t-case is an NP229, which is a full time 4wd system with a viscous coupler (VC). So the typical "go make sharp turns in gravel" won't always work. But you can try it. Find a big gravel parking lot, engage 4wd, and make a really sharp turn while watching the front inside tire. If the VC is tight, you may see it want to turn at a different speed than it otherwise would. And then while in the tight turn, blip the throttle a bit and see if that front tire spins. A bad VC will act like an open differential which means you can spin a front tire by itself.

If the above is inconclusive, you could jack the front end up off the ground and put the axle on jackstands so the tires aren't touching, make sure the Jeep is in PARK, and rear tires are chalked. Shift it into 4wd (engine will either need to be running, or better yet, use a vacuum pump to do it by hand), and then try to turn the front drive shaft by hand. If the VC is in good shape, it will be hard to turn, if you can at all without a wrench. If the VC is worn, it will be easier to turn. And if its in 2wd, the only resistance will be what the front axle and tires provide, which you can verify by shifting it into 2wd and spinning the shaft.
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chevelleguy
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Re: 2wd to 4wd 1988

Post by chevelleguy »

I will sometimes confirm it’s in 4WD by shifting it to Lo range. To do that, I find it works best to come to a stop, foot on brake, shift trans to neutral to release all pressure on the drivetrain, then shift to park but keep your foot on the brake, lift up on range shifter.


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Johnzi10
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Re: 2wd to 4wd 1988

Post by Johnzi10 »

You can climb under the Jeep and inspect where the shift vacuum switch moves the linkage to the transfer case. I believe that it is 2wd when the lever is toward the front of the vehicle. I know this because I lost/ didn’t have the clip that held the linkage rod together. New clip, had 4wd.
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Johnzi10
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Re: 2wd to 4wd 1988

Post by Johnzi10 »

Image
Image


These pics show the shift vacuum switch and the t case lever.


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2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

rocklaurence
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Re: 2wd to 4wd 1988

Post by rocklaurence »

Johnzi10 wrote: Tue Aug 09, 2022 6:33 pm You can climb under the Jeep and inspect where the shift vacuum switch moves the linkage to the transfer case. I believe that it is 2wd when the lever is toward the front of the vehicle. I know this because I lost/ didn’t have the clip that held the linkage rod together. New clip, had 4wd.
Yes, confirm that the Tcase lever moves. Majority of vacuum shift issues are leaks and a failed shift mechanism. The vacuum motors are not made any more. So, you'd have to locate a working used one or go to a Mechanical shift replacement.
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