Diff Q - need help!

[TOOLman]

I managed to damage the rear axle of my ZJ and had to have it replaced. The shop installed a used D35 axle, but I'm uncertain of whether or not it has a limited slip diff, like my old one.

I thought you could check this by raising the rear end of the Jeep and turning one of the wheels (in neutral). With an LSD the wheel on the other side should spin in the same direction as the one you're turning. Without a limited slip the other wheel would spin in the opposite direction.

This was the case with my old axle, but with the "new" one the other wheel spins in the opposite direction. Also, there is no LSD tag on the pumpkin (I realize that's not conclusive).

The mechanics at the dealership say that A) you can't test for the presence of an LSD this way; and B) all 4WD Grand Cherokees have an LSD in the rear.

Can anyone tell me if I'm completely wrong here, or if the mechanics are?

[John McC]

TOOLMan,

It gets confusing as we go back and forth between forums. but I can at least confirm that in NA not all 249 ZJs have LSD (front back or middle!).

If you put the transfer case in neutral and try rotating you should get the same reaction, but the impact of an LSD is the same whether the vehicle is 2 or 4 WD. There is nothing special about the diff itself in a ZJ.

John

[TOOLman]

Thanks, John (for both your replies :)).

I haven't posted in the JU GC forum for over six months, but the disappointing lack of replies on ILJ made me take a chance. Apparently the tech quality over there has improved. There were 20 replies to my thread a minute ago (of course some of those were mine).

I hate those time differances. Why do you guys have to sleep until 2 pm and stay up all night, instead of keeping normal hours? :)

[The Man with the Plan]

In an open diff, if the drive-shaft is immobilized, and you spin one tire, the other tire will rotate in the opposite direction.

Sounds to me like you have an open diff in there. If there was too much friction in the t-case, the force of your hand spinning the wheel probably wasn't enough to overcome it.

[Warlock]

Like John said, not all have LSD's, at least here anyways. Imports are a different story though. Some have different rulings as to what is stock and what is not.

Maybe the imports do have a LSD. I don't know for sure.

But, I always thought you could check for the LSD by rotating the tires and watching what the other one does.

And I think you are working the weird hours :D It should be about 3 AM there as I type this I think.

[John McC]

Tommy,

Upon reflection, here goes:

The only difference between a 249 equipped ZJ and any other rear wheel drive vehicle is how the power is distributed between the front and rear differentials. Power sent to the rear diff is sent down the same rotating drive shaft just as it would be if it was a conventional rear wheel drive car. The differential in the back (or the front) is no different in how it handles the power, i.e. it is a conventional gear spider differential. If there is no LSD (i.e. an open diff) then when you rotate one rear wheel in the direction of forward travel the wheel on the other end of that differential will be compelled to rotate against the direction of travel because of the way the gears work with each other inside the pumpkin. If there is a LSD than the clutches will tie the two axles together and cause the two wheels to rotate in the same direction of travel.

Your mechanic may be well meaning, but he is technically challenged. Of course if he wants to dig in then the only way to resolve it is to remove the diff cover, and then it will be obvious to everyone.

It is probably not too helpfull to point it out, but for the amount of money your insurance company has paid so far, you could have imported a new rear end or even a reconditionned one) from NA!

Good luck, I am looking forward to the happy resolution of this one.

John

[EDPMEDIC]

Let me ask you this when you say axle do you mean the whol rear end or just the rear axle? In either case it should have a rear cover. I would hope the gear oil was changed and if it wasn't Do it. Then you could tell what you got for sure Good Luck:xj: :usa: :usa:

[TOOLman]

John - that's exactly how I understood it. Thanks.

EDPMEDIC - I'm not sure of the difference (language thing). I guess it's the whole rear end (axle, housing, diff; everything between the wheels). The suspension, sway bar, and control arms have not been replaced.

This weekend a new noise appeared, and there is a severe vibration when accelerating up a hill. I'm going to demand a new axle, no two ways about it. If they claim that this axles has a Trac-Loc, they'll have to open it and show me (it's not my job).

[Warlock]

axle, the part that goes in the axle tube and intermixes with the gears

rear end, differential housing and gears (including axles)

HTH with the language thing :D

It sounds as if the entire differential was replaced.

[TOOLman]

Yeah, with that terminology they replaced the entire rear end.

[jeepbob]

A wore out trac-loc will act just like an open diff and the wheels will rotate in opposite directions when one is spun.

[TOOLman]

I'm aware of that. Since my old diff did act the way it was supposed to, and the "new" one didn't, I thought that it was either worn out or didn't have an LSD in the first place. In either case, it wouldn't have been an equivalent replacement.

It turned out that the "new" diff did turn the other wheel in the same direction, provided that the tranny wasn't in Neutral. When I thought back, it struck me that that was how I tested my old diff, too. And according to the mechanics (yeah, I know...) the diffs were exactly the same. They claim to have opened both, to compare.