Mode of failure for LSD?

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blasphemy101
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Mode of failure for LSD?

Postby blasphemy101 » Tue Jan 13, 2015 7:38 pm

Will our standard clutch-type LSDs start to slip as they head towards failure?

At the last autocross, the car was revving up like the clutch was slipping as I was exiting a big, second gear hairpin. I know my clutch slips in higher gears when I'm running 15+ PSI, but this was only at 12, and it only occurred at this point in the course. A friend was running into issues with his open diff on this section, so that made me think maybe my LSD is going out. It might also be useful to mention that in the past, I noticed the car seemed to rotate in one particular direction (left) whenever I got wheelspin. I had a feeling this was due to a wearing LSD.

If this is the case, is this an easy fix? I'm sure it is covered in the write-up, but I don't want to bother rebuilding the diff if the material from a slipping LSD clutch pack has likely destroyed the LSD.
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Re: Mode of failure for LSD?

Postby Yoshi » Wed Jan 14, 2015 4:38 pm

It's a clutch type. works just like transmission clutches do. Then they go, they don't grab anymore. When they don't grab anymore, you get one tire fire. Especially boost will show any dying clutches and it will also cause it to wear faster.

The issue is that the inner most portion of the LSD is 100% NOT serviceable. The material actually destroys the tools most machinists will use. If you've destroyed the center meat, all is lost and the unit is toast. I think you can get other innards and it'll work. I'm not sure. Basically, crack open the diff and see how damaged the center section is. If it's ok, you can reclutch, maybe add more, and go.
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Re: Mode of failure for LSD?

Postby M20_fever » Wed Jan 14, 2015 7:01 pm

keep in mind stock e30 LSD is only 25% lockup. I get inner wheel spin on hard corners a lot. If you want to do a quick and free test, unbolt one side of your rear sway bar next time your at an event. That should greatly improve the spinning issue, it did for me.
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Re: Mode of failure for LSD?

Postby blasphemy101 » Fri Jan 16, 2015 5:46 pm

M20_fever wrote:keep in mind stock e30 LSD is only 25% lockup. I get inner wheel spin on hard corners a lot. If you want to do a quick and free test, unbolt one side of your rear sway bar next time your at an event. That should greatly improve the spinning issue, it did for me.


I had not thought of that. If I notice it again, I will try disconnecting the swaybar. If this is the case, I need to get it resolved before I cause unnecessary damage to the LSD.

Yoshi wrote:It's a clutch type. works just like transmission clutches do. Then they go, they don't grab anymore. When they don't grab anymore, you get one tire fire. Especially boost will show any dying clutches and it will also cause it to wear faster.

The issue is that the inner most portion of the LSD is 100% NOT serviceable. The material actually destroys the tools most machinists will use. If you've destroyed the center meat, all is lost and the unit is toast. I think you can get other innards and it'll work. I'm not sure. Basically, crack open the diff and see how damaged the center section is. If it's ok, you can reclutch, maybe add more, and go.


That makes sense. If the LSD is dying, it must not be too far gone. It definitely spins both tires from a stop, and I didn't notice it slip anywhere else on the course except that one particular turn. I drove another car with an open diff, and it was giving the inside tire a pretty good workout. Automatic trans and an open diff... the car felt like a dying animal on that corner...
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Re: Mode of failure for LSD?

Postby M20_fever » Sat Jan 17, 2015 4:39 am

Exactly how mine feels when the wheel lifts. No saw in the rear, and the J-stock rear spring rate greatly helped, but didn't eliminate the issue.
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