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  #1  
Old 04-07-2009, 09:45 PM
cmac2012's Avatar
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BMW rear end: LSD?

LSD - Limited Slip Differential. What? What did you think I meant?

I've been noticing a noise now and then in my rear end, my Bimmer's rear end, usually only at low speed while making a sharp turn.

A few week back, I had the rear up on jack stands for something, and I forget why, but I turned one of the tires and I noticed the one on the other side turned in the same direction. It was in neutral, but my experience in the past had been that the planetary gear in the diff would make the other tire turn the opposite direction, even while in neutral.

So I put it in gear and the tire/wheels would only turn with some difficulty, making a hell of a grating sound. Then I'd put one tire on the pavement and the free wheel would behave the same on turning. Are these things posi-traction, limited slip? I've never had a posi-traction rig before so I'm not familiar with how they work, or behave anyway.

Now I'm wondering if that noise is the posi. breaking loose when it goes around a sharp turn. And worse, is it only a matter of time before this thing goes? I recently changed the oil. It was making the noise before that.

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Old 04-07-2009, 09:50 PM
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Can't speak to your beamer lsd issue, but back in the day, GM posi rears needed a special oil. I believe it was whale oil? Very expensive. If you did not use it, the dif. would make all kinds of noises, and tended to bounce around a corner.

Maybe you need to change your dif fluid, and use the correct BMW stuff?
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Old 04-07-2009, 09:55 PM
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Hmmm . . . I recall researching it somewhat and IIRC, all leads said to use reglar old 80 or 90 weight diff oil. But more searching is in order. Bimmerfest had no answers for me. I'll try some others.
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Old 04-07-2009, 10:16 PM
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Many limited slip differentials require a lubricant additive called a friction modifier.
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  #5  
Old 04-07-2009, 10:20 PM
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E30 right?


I will ask a buddy whos into E30s and see what your supposed to use.
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  #6  
Old 04-07-2009, 11:31 PM
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I just tried BimmerForums and a couple of guys are big on Amsoil 75w-90. One guy described the same noise I'm getting and said that improved lube fixed it.
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Old 04-08-2009, 06:11 AM
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A lot of bimmers have limited slip. We had a 318i...a pretty basic four cylinder four door with a five speed for a while. It had it.

I don't recall it clunking but gm diffs are notoriously clunky backing or turning at low speeds.

And yes usually a special diff lube is required, if its a clutching diff, but not using it simply makes the diff not act correctly. I don't believe it will cause wear problems.
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  #8  
Old 05-11-2009, 09:43 PM
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Quote:
Originally Posted by PaulC View Post
Many limited slip differentials require a lubricant additive called a friction modifier.
I went to my local friendly Amsoil dealer to get some 75w - 90. They had an 8 ounce bottle of something that has to be what you're referring to -- described as such on the bottle, called 'slip-lock' or something. It was only $8 but I was curious if the Amsoil alone would do the trick and whattayaknow, it did. Two quarts at about $10 each.

Noise gone. Next problem (he said, oozing over-confidence).
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Old 05-11-2009, 09:55 PM
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Quote:
Originally Posted by cmac2012 View Post
I went to my local friendly Amsoil dealer to get some 75w - 90. They had an 8 ounce bottle of something that has to be what you're referring to -- described as such on the bottle, called 'slip-lock' or something. It was only $8 but I was curious if the Amsoil alone would do the trick and whattayaknow, it did. Two quarts at about $10 each.

Noise gone. Next problem (he said, oozing over-confidence).
You didn't say if you bought the slip-lock stuff or not.

If so, don't bring it in the house. That stuff has a stink that oozes right through the container.
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  #10  
Old 05-11-2009, 10:26 PM
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No, I didn't buy it but good tip anyway. Might be in my future somewhere. I gambled on not needing it and it worked out. I could have always bought some later and I hate returning stuff.

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