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Old 05-02-2014, 11:29 PM   #1
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4wd vacuum bypass and back to vacuum

When I first purchased my jeep I discovered the 4wd was not working. No big deal, I just bypassed the vacuum system for a while by just flipping the actuator upside down and bolting it back to the the axle (after sliding the sleeve over into the locked position). This locks everything in place without having to add washers and shims and/or removing and replacing those "pain in the ass"clips. It's 4 bolts and takes 5 minutes. The 4wd works flawlessly this way. I did this to my jeep within 3 days of owning it. After driving it for a while I discovered I was only getting 11mpg. I decided to fix the vacuum system and "unlock" my front drivetrain in hopes of increasing my mpg's. My problem was that my red 4wd vacuum line (which supplies vacuum to the system) had been cut and no vacuum was being supplied to the 4wd switch. I spliced my 4wd vacuum supply line into my distributor vacuum (with a t connect) and flipped the actuator back "right side up" and everything works like it is supposed to now. Including my 4wd indicator light!!!!! It seems like there is less drag on the jeep now (May just be a placebo) but I hope it increases my gas mileage. I will update any mpg improvements when I have the results. Anyone wanna give predictions on mpg improvements I could hope to see? I'm really hoping for at least 2 mpg improvement. Otherwise I will just go back to the bypass and keep it locked up.

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1988 Jeep Wrangler 4.2
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Old 05-06-2014, 10:24 PM   #2
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I didn't notice much difference when mine was always locked but post up your results.

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Old 05-11-2014, 09:50 PM   #3
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I have a Posi-loc on mine and I have ran it with the front locked in and in 2Hi just to see, because a lot of folks say it makes no difference, On My Jeep it about 3MPG less with the front rolling all the time.

4.2 Auto, 3.07 gears and 29" tires.
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Old 05-19-2014, 03:48 PM   #4
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Thanks guys. I haven't actually checked the mileage yet but it seems a lot better from guesstimating.
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1988 Jeep Wrangler 4.2
Nutered and Weber Carb
4" Pro Comp Lift
32x11.50 Cooper Discoverer STT
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