gnosis

Greetings,

I have my suspicions that my Torsen LSD isn't limiting slip anymore. If it is, it's not doing it anywhere near as well as it used to. I have tracked my car quite a lot in the past, and even with only 40% lockup it was useful, but these days even around the road at snail speeds I can sense little ability to limit slip of the inside wheel.

I don't know how these units work, what wears, and what, if anything, can be fixed. Any info appreciated.

Clayton

BruceWard

Im curious, how many miles does it have on it?

gnosis

156000km (99000 miles), with quite a few trackdays.

Jason Judd

To my knowledge there are plates within the LSD which can indeed wear out.

The good news is that they can be replaced, too.

Jason

gnosis

Does the Torsen type have plates? Does anyone have the instructions/parts to rebuild one of these? I'd rather do it myself if the instructions are available.

Clayton

RajDatta

Torsen's use worm gears and clutch types use plates. You can rebuild clutch type lsd's and fine tune them for how much lockup you need but torsen units cannot be rebuilt.
Your lsd maybe worn out, time for a GT or a Quaife unit? Time to get some professional opinion .
Raj

Jason Judd

Raj,

Torsen types can't be rebuilt?

Man that sucks...my luck!

Jason

RajDatta

Jason, torsen types are much more robust and don't require rebuilds that often, so there goes your luck!

Raj

gnosis

Well if the consensus is that 100,000 hard miles is perfectly capable of wearing out a Torsen diff, then I reckon that describes my situation.

Next question. What's the highest percentage of lockup that can be tolerated for daily driving with minimal downside, so that when I take it to the track I can get the most benefit. Did the Turbo S have 75% lockup? Somewhere between 40% and 75% sounds pretty nice to me.

Clayton

RajDatta

I am planning on installing a turbo S trans in the near future, should be in in no more than 3 months so I can give you 1st hand impression then. From what I understand, the lockup only comes into play when there is slippage.
You can get any kind of lockup you like. I plan to run 75% lockup cause thats what the factory used on their turbo cars. 40% lockup is hardly ever evidenced, so I think there is room to go higher depending on what your focus is.

gnosis

That will be interesting. I hope you can take some photos and post them while you're at it.

Was the Turbo S diff a ZF or a Torsen?

I've done some reading into the differences between Torsen and clutch-type diffs (ZF), and I can't see how a Torsen can be defined as having a lockup of a certain percentage. There's a torque bias ratio that determines what multiple of torgue can be applied to the gripping wheel relative to the slipping one, but how this translates into a locking percentage I don't know. However Porsche notes that both types have a locking factor of 40%. Can anyone enlighten me?

Is there any way to determine which type my car was shipped with? Both types are referred to as M220, which isn't helpful. Since the diff is enclosed in the tranny I doubt there's any visual indicator. Is there a practical test I can do to prove which type I have (irrespective of it being possibly worn)?

Clayton

RajDatta

All cars at some point in 1993 were changed from clutch type to torsen type. I will try to see if I can get some pics.
Not sure if the turbo S lsd is clutch type or torsen but it would make more sense if it was clutch type.

TonyG

Tosen differentials cannot wear out with respect to torque applied to each respective wheel.

Thus, if you really have a Torsen differential, it has the exact same characteristics it did the day it was installed.

There are no clutch plates to wear. The Torsen is purely a mechanical device with nothing to slip.

Perhaps you do not have a Torsen differential? Perhaps it's a clutch pack differential type LSD? Are you the original owner of the car?


TonyG

gnosis

Tony,

I'm the original owner, and the whole transmission is both original and has never been out of the car except to change the clutch. What the dealer did with it while it was out of the car is anyone's guess, but it wouldn't surprise me in the slightest if they accidentally put someone else's transmission back in by mistake. Since the car is a 1995 model, that's the only scenario I can think of that would allow it to be anything but a Torsen.

Since I've had the experience of open diffs, locked diffs, as well as this Torsen unit over the years, I think I'm pretty good at sensing when it's doing it's job properly, but I find it very strange that it doesn't seem to be providing much limiting force anymore, especially in light of your comment that Torsens can't wear out and loosen up.

I'm going to replace the clutch soon, so I'll open up the diff and have a look inside while I'm at it.

Clayton