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Old 02-15-2011, 09:52 PM   #1
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front axle vacuum

ok was wondering if im thinking about this right.the vaccume is to lock the hubs in insted of manual lock hubs?just wondering why they would do this if thats what it does.on my 96 cherokee i dont remember anything like that.knowing this i might get the lock system for it so i dont have to worry about it failing sometime when i need it.thanks for the info in advance.im just used to the older cj style lockouts.

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Old 02-15-2011, 11:30 PM   #2
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I had a same issue on my 87 XJ with the split shaft--- so when I did the lift on it the guys put a solid axle in--- no more issue

I agree-- I wish for manual lock outs like my Sami had

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Old 02-15-2011, 11:39 PM   #3
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The hubs are fixed. The vacuum operates the central axle disconnect (CAD). The passenger side axle in the front end is made up of two pieces which are locked together by a vacuum actuated collar when the transfer case is shifted into four wheel drive.
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Old 02-15-2011, 11:51 PM   #4
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Tyewilly is right. I can't say I know the exact reasoning behind it, but I suspect it was to keep the front driveshaft stationery during 2WD for wear purposes, plus you wouldn't have to bother balancing the shaft in that case. Probably a cost-cutting tactic. But at the same time add the "convenience" of locking the shafts in without having to leave the vehicle. Hard to tell sometimes since AMC/Chrysler made all sorts of crazy additions/changes to the YJ that didn't make sense.
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Old 02-16-2011, 12:12 AM   #5
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It is a fuel effeciency issue. When you disconnect it you have less metal spinning around. All that spinning takes up power whether it is directly from the engine or increasing the rolling resistance of the front wheels.

There is also a wear issue, but you also want to use it every now and then so it doesn't freeze up.

The reason for vacuum locks as opposed to manual, as stated earlier is for convience, one so you don't have to get out of the car, and the other is to make sure you do both, people have been know to lock one and forget the other or forget to unlock one. Then you have weird balance issues.
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Old 02-16-2011, 07:41 AM   #6
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so when vac locked in its still a limited slip diff?my xj didnt even have a vac on it nore manual hubs so this diff is new to me.
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Old 02-16-2011, 10:43 AM   #7
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The Vac lock on the axle does not change whether the differential is limited slip, it just changes whether the Differential and Wheels are connected. I've never owned or driven a XJ it may have an electronic hub locker if it doesn't have vacuum. That is assuming the hubs aren't always locked.
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Old 02-16-2011, 12:35 PM   #8
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No front axle has limited slip. Your LSD is in your rear axle and is always active.

Newer XJs (92-01) have no CAD. They have a solid passenger shaft, just like the TJs.

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