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What the heck is this ball mounted behind my d35.

Mike1331

NAXJA Forum User
Location
Folsom, CA
I tried to do a search but no luck. I've got a little ball on my 89 cherokee right behind the right (right side if sitting in driver seat) side of my stock d35. Its mounted on the axel and has a plug going into it. Could this be some type of solinoid or vacume motor for a stock limited slip front differential? My friend did not have this on his 96 xj.
 
Mike1331 said:
I tried to do a search but no luck. I've got a little ball on my 89 cherokee right behind the right (right side if sitting in driver seat) side of my stock d35. Its mounted on the axel and has a plug going into it. Could this be some type of solinoid or vacume motor for a stock limited slip front differential? My friend did not have this on his 96 xj.

I think you have your axle identification wrong. If you are talking about the FRONT axle, then it's a Dana 30 (The D35 is in the rear).

The little "ball" you are refering to is most likely the vacuum disconnect motor. 1989 and earlier XJ's had a "split" (3 piece) front axle with a 231 Transfer case. When you engage 4H or 4L, a vacuum switch causes a "collar" to lock the passenger side stub axle to the main axle shaft - giving you 4WD traction capability on the passenger side wheel. If those "plug" wires (actually vacuum lines) come off, the collar will not activate and engaging the front driveshaft on an open D30 would provide no traction, since all power of the diff would be sent to the unconnected passenger side main shaft.

Later model year XJ's just had a standard two piece D30 axle.

Your configuration is normal for an '89, as your buddy's is for a '96.

Mike in NJ :patriot:
 
Right D30 Sorry, It's been a while since I've talked about the xj, Mines been out of commission for about a year.
So your saying ONLY the right tire is spinning when 4hi or 4lo is engaged. And of course doesn't when unplugged. Thats kind-of shitt*y. Another thing to worry about when on the trail. I did notice that it was going back into the t-case. Plug is kind of corroded. Are these expensive.
 
Mike1331 said:
So your saying ONLY the right tire is spinning when 4hi or 4lo is engaged. And of course doesn't when unplugged. Thats kind-of shitt*y. Another thing to worry about when on the trail. I did notice that it was going back into the t-case. Plug is kind of corroded. Are these expensive.

No, not just the passenger side tire. As with ANY open diff (front or back), only one side (either side) of the axle will pull. It will send the traction to the side which is slipping most.

Trouble on the vacuum disconnect axle is that, if the collar doesn't engage - the "center" axle shaft is not attached to anything, so it gets all of the torque, and the driver side axle shaft doesn't get a chance to pick up the slack.

One advantage of the v-disconnect is non-trail related. When you are in 2WD, the front axles/wheels are spinning free - no d/s drag at highway speed.

By the way, unless you're running BIG tires (which would introduce a strength issue), there actually is an advantage to having a V-disconnect on the trail. If you had a locker in the D30, and added a manual vacuum switch to control the collar - you could have the advantage of "3" wheel drive Low range. Can come in handy when you facing tight turns in a rock crawl.

The vacuum plugs are an easy junkyard acquisition. Plenty of older XJ's in there.

Mike in NJ :patriot:
 
Mike in NJ said:
No, not just the passenger side tire. As with ANY open diff (front or back), only one side (either side) of the axle will pull. It will send the traction to the side which is slipping most.

Trouble on the vacuum disconnect axle is that, if the collar doesn't engage - the "center" axle shaft is not attached to anything, so it gets all of the torque, and the driver side axle shaft doesn't get a chance to pick up the slack.
Mike in NJ :patriot:


To clarify how a differential works: An open differential always divides TORQUE equally between sides. If the left tire slips due to lack of traction, the torque to the right side is limited to the level that the left broke traction at. At the extreme, say the left tire is off the ground. No torque required to turn a wheel that's off the ground, so the right side gets no torque, even though it may have traction on the ground, so you go nowhere.
The other end of the spectrum is a fully locking diff. such as a ARB or Detroit locker. This type can bias torque 100%. This means that in the same case of the left tire off the ground, the locker can bias 100% of the torque to the right. Meaning it can still apply torque to the limit of whichever tire has more traction.
A limited slip lies somewhere in between, some even tell you what the torque bias ratio is. If the ratio is, say, 2:1, then the differential can send 1/2 the torque that it took to break traction on the left side to the right side.

Brian
 
explorer said:
To clarify how a differential works: An open differential always divides TORQUE equally between sides. If the left tire slips due to lack of traction, the torque to the right side is limited to the level that the left broke traction at. At the extreme, say the left tire is off the ground. No torque required to turn a wheel that's off the ground, so the right side gets no torque, even though it may have traction on the ground, so you go nowhere.
The other end of the spectrum is a fully locking diff. such as a ARB or Detroit locker. This type can bias torque 100%. This means that in the same case of the left tire off the ground, the locker can bias 100% of the torque to the right. Meaning it can still apply torque to the limit of whichever tire has more traction.
A limited slip lies somewhere in between, some even tell you what the torque bias ratio is. If the ratio is, say, 2:1, then the differential can send 1/2 the torque that it took to break traction on the left side to the right side.

Brian

Of course, what I meant to say! :D

I just rushed describing the "effect", and this description is more precise.

Good job Brian.

Mike in NJ :patriot:
 
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