4x4 vacuum hubs


5ow

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how do you know if you have the dreaded vac hubs? my production date is 12/99 if not vac hubs what do i have and whats the pros and cons of what i have thx,scott
 


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I don't know the specific history. But there are several articles in the "How To Tech" section of this site that refer to the PVH (pulse vacuum hubs) system being used from 1998 to 2000. So, if you don't have little turn knobs on your hubs to engage or disengage them manually, then you most probably have vacuum hubs.

The Pro for PVH is that if the system is working, you don't have to get out of the vehicle to manually engage or disengage the hubs when you want to use 4wd. The Con is that the system doesn't seem to be very reliable, probably due to potential vacuum leaks or problems from dirt, corrosion or lack of lubrication.

Follow the "How To Tech" link at the top of the page and you can learn a good bit about the PVH system and options to get around it.
 

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The PVH system was actually one of Ford's better auto hub designs at the time, the problem was that it had very little longevity, and once it broke it was expensive to fix, and hard to diagnose.

I'd look at swapping to manual hubs, or a live axle setup if you are having problems with it.
 

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5ow

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thank you for your info, i called ford with the vin and they couldnt tell me, so i will pull the center cap-rim this weekend, if i have the later style live axle then what are those pro and cons?
 

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Live axle has .3-.4 less MPG than unlocked front axles
And 100% less trouble than PVH axles
 

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When you look at the hub, does it have a nut? (live axle) or not (vac hub)

Vac hubs provide slightly better fuel economy - not turning the front differential gears/front driveshaft/transfer case output shaft/transfer case chain. All of the aforementioned parts last longer therefore. Disadvantage: Not as strong; can fail to engage when most needed.

Live axle is opposite.
 


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