LOST JEEPS :: View topic - Aluminum front dif housing and TAD's

the pinion does not break the housing by climbing the ring gear. the teeth on the pinion are helical cut, and depending on the direction of cut, when too much force is applied it tries to either pull it's self into the ring gear or away from the ring gear. when you are loading and unloading the front diff by spinning the tires and then having the tires grab when it gains traction, the ring gear tries to stop turning while the pinion still has a lot of rotational energy from when it was spinning freely. if the housing is built strong enough to resist the movement of the pinion into or away from the ring gear, the energy is then transfered into the ring gear and the tires begin to spin again. if the housing can not hold the force trying to move the pinion in or out, it stresses the case until it cracks and fails

Author:	greiswig [ Sat Dec 24, 2005 6:21 pm ]
Post subject:	Aluminum front dif housing and TAD's
Hi, all, I've heard that locking differentials are not recommended for the front of Libby's, because of the aluminum housing. I gather at least one person has broken the housing? I'd sure be curious to know what caused the breakage, and where the failure was in the housing: is it the pinion trying to "climb" the relatively stationary ring gear? Reason for wanting to know is this...if a locking differential causes this, it seems to me that the new ESP system that comes on the 2006 model would cause the same effect, just using a different mechanism. True, the mechanical stresses of a sudden lockup using a locker might be different from the ESP, but the ESP would be pretty similar to a limited slip dif, wouldn't they?

Author:	krazz1e [ Sat Dec 24, 2005 6:35 pm ]
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it's the housing that cracks, the gears are just fine. it fails due to excessive wheel hop and landing hard on a wheel, this transfer the engery to the weakest point which is the housing. a trutrac is theory would reduce wheel hop because it generates better traction, so who ever told you that don't know the facts, plenty of guys here running tt up front and no breakage. I'm considering a aussie locker up front, they are cheap. Not sure how ETC works exactly so cannot comment on that.

Author:	skrracing [ Sat Dec 24, 2005 9:04 pm ]
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I have had the True Trac in the fornt of both of my KJs without any problems. But then again...I just go to the mall. Later...Clint Mall Parking...

Author:	GPR65 [ Sat Dec 24, 2005 10:46 pm ]
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Clint do you have the preferred parking at the mall. I never get the good spots! Chris

Author:	greiswig [ Sun Dec 25, 2005 2:26 am ]
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krazz1e wrote: it's the housing that cracks, the gears are just fine. it fails due to excessive wheel hop and landing hard on a wheel, this transfer the engery to the weakest point which is the housing. a trutrac is theory would reduce wheel hop because it generates better traction, so who ever told you that don't know the facts, plenty of guys here running tt up front and no breakage. I'm considering a aussie locker up front, they are cheap. Not sure how ETC works exactly so cannot comment on that. I knew the gears didn't break, but it's conceivable that the pinion gear could punch its way through the top of the housing trying to climb the ring gear. That's what I was wondering about. Are you saying that the slip joints in the axle shafts bind up or something and transfer the impact of wheel hop up to the housing? Or is it that the sudden jolt when the wheel comes down spinning and grabs traction does it? Oh, and what's an "aussie locker?" Thanks!

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Author:	the1jferg [ Sat Dec 24, 2005 10:15 pm ]
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Author:	hankwood [ Sun Dec 25, 2005 4:42 am ]
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the pinion does not break the housing by climbing the ring gear. the teeth on the pinion are helical cut, and depending on the direction of cut, when too much force is applied it tries to either pull it's self into the ring gear or away from the ring gear. when you are loading and unloading the front diff by spinning the tires and then having the tires grab when it gains traction, the ring gear tries to stop turning while the pinion still has a lot of rotational energy from when it was spinning freely. if the housing is built strong enough to resist the movement of the pinion into or away from the ring gear, the energy is then transfered into the ring gear and the tires begin to spin again. if the housing can not hold the force trying to move the pinion in or out, it stresses the case until it cracks and fails

Author:	FreedomKJ [ Sun Dec 25, 2005 11:33 am ]
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Someone should add Hank's explaination to the Tech section. I think that's the clearest one I've heard so far.

Author:	greiswig [ Sun Dec 25, 2005 11:29 pm ]
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hankwood wrote: the pinion does not break the housing by climbing the ring gear. the teeth on the pinion are helical cut, and depending on the direction of cut, when too much force is applied it tries to either pull it's self into the ring gear or away from the ring gear. when you are loading and unloading the front diff by spinning the tires and then having the tires grab when it gains traction, the ring gear tries to stop turning while the pinion still has a lot of rotational energy from when it was spinning freely. if the housing is built strong enough to resist the movement of the pinion into or away from the ring gear, the energy is then transfered into the ring gear and the tires begin to spin again. if the housing can not hold the force trying to move the pinion in or out, it stresses the case until it cracks and fails Thanks for the explanation. I know helical gears push and pull along the pinion, but I bet there is also a fair amount of force perpendicular to the pinion...otherwise we wouldn't be driving the ring gear very efficiently. It would sure be interesting to see one of the failed housings to see what happened. But it sounds like shock loading is the key either way. In my experience, a locking differential actually tends to make for LESS shock loading rather than more. Something optimistic about that. Thanks again!

Author:	hankwood [ Tue Dec 27, 2005 5:36 pm ]
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there is definitely a large amount of force applied to the pinion. i've seen them where they snap the pinion at the end of the inner bearing, and i've seen ring gears with teeth sheared off by the pinion. as for shock load, a locking differential doesn't affect that. the locker increases the potential traction of the tires, which in turn reduces the chances of shock load from tire spin. of course, if you put one of the new hemi engines in the kj, you could shock load the diff from the input side. which is why gears for drag racing are softer than gears for street use. the softer gear allows for some absorbtion of the shock load when the drag car launches, instead of shearing the teeth off of the ring gear. unfortunately soft gears would be worn out in a few thousand miles if used on the street.

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