[sasilverbullet]

I'm pretty mechanically inclined, but I'm confused as to why my 968 has option code 220, which is Locking Differential, and everyone calls it a LSD, Limited Slip Differential.



Could someone please explain why these have different names but refer to the same item?



Thanks everyone! <img src="/forum/images/smilies/968/tongue.gif" class="smilie" alt="" />

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[Greimann]

Consider that a conventional differential is a "slip all the time" design. If the slightest difference in traction exists between the two wheels, all the torque goes to the wheel with the least traction. It really just makes going around corners easy.



In a limited slip diff, the two sides are locked so that torque is applied evenly to both tires in uneven traction situations. They only unlock when the torque differential exceed a certain limit so you can still turn the corner into your driveway without snapping an axle.



So a limited slip diff is locked sometimes, and slips when necessary.

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[ether_joe]

thanks Griemann I actually had the same question myself.

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[IceWater]

Depending on what year your car is, it could have either a clutch-type lsd or a torsen lsd. A clutch type works based on a speed difference between the two wheels. Normally the wheels are not locked together at all. When one wheel starts to spin faster than the other one, a clutch begins engaging that starts to bind the two together, increasing the torque to the wheel with traction. The torsen (torque-sensing) type works based on torque difference between the two wheels. Again, the wheels are normally not joined together, but when one wheel starts to lose traction the torque difference between them causes the gear train to begin binding up, sending more torque to the wheel with traction. One advantage of the torsen is that it doesn't cause any binding just from the normal speed difference between the two wheels that results from turning. One disadvantage is that it can only provide a multiple (around 5X) of the torque of the bad wheel to the good wheel. So if the bad wheel is in the air or on slick ice, there's still very little torque available to the good wheel. 92 and early 93 968s had clutch types, then they switched to torsen.



Tom

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[sasilverbullet]

Thanks! Now I know why my LSD is a "locking differential"



Now anyone know how to tell if it's a clutch or torsen?

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[flash]

this might help explain how these things work:



http://www.guardtransmission.com/velocity.htm

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[wjk_glynn]

[quote name='IceWater' date='Mar 1 2006, 06:55 AM']...A clutch type works based on a speed difference between the two wheels. Normally  the wheels are not locked together at all. When one wheel starts to spin faster than the other one, a clutch begins engaging that starts to bind the two together, increasing the torque to the wheel with traction...[/quote]





Hi Tom,



I think Griemann's explanation (quoted below) for the clutch type applications is more accurate - i.e. the clutches are constantly engaged and its only when the torque difference between the two half shafts exceeds a certain limit that you get some slip.



As I'm sure you know, the classic experiement is to jack up the rear of your car, put the transmission in gear, disengage the hand brake then and slowly turn one rear wheel.



* If the other rear wheel turns in the opposite direction, you have an open diff

* If you're not physically able to turn the rear wheel, you likely have a LSD - or you forgot to release the handbrake ;-)



Now if your explanation about how a clutch type LSD was true, then a human would still be able to turn the rear wheel because a human wouldn't have enough power to "spin" up clutches to engage some type of centrifuge clutch effect. But the fact that you can't turn it in practice (when there is a clutch type unit installed), is an example of how the clutches are constantly engaged.



Karl.



[quote name='Greimann' date='Feb 28 2006, 09:53 PM']...In a limited slip diff, the two sides are locked so that torque is applied evenly  to both tires in uneven traction situations. They only unlock when the torque differential exceed a certain limit so you can still turn the corner into your driveway without snapping an axle. 

 

So a limited slip diff is locked sometimes, and slips when necessary.[/quote]



PS - I'm not sure what would happen if you turned the rear wheel in the case of a torsen diff...

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[flash]

they spin opposite direction just like an open diff, at least with my GT unit they do

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[Harvey]

[quote name='flash' date='Mar 1 2006, 11:20 AM']they spin opposite direction just like an open diff, at least with my GT unit they do

[right][post="16781"]<{POST_SNAPBACK}>[/post][/right][/quote]



Sooo...is there any visual way to tell if you have LSD/Torsen on your by looking at the tranmission or its numbers? Or do they all look the same on the outside?



Harvey

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[wjk_glynn]

[quote name='flash' date='Mar 1 2006, 11:20 AM']they spin opposite direction just like an open diff, at least with my GT unit they do[/quote]



And I presume that's a GT torsen unit?



Karl.

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[flash]

yes - a GT torsen unit - sorry



i don't know of any way to tell visually, but there might be - that's one for bobby - he'd know better than anyone

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[S_Cal968]

Locking is not really the correct term - clutch style diff's are defined in percentage of engagement. The engagement is < 100% - hense the name "limited slip". And, the percentage can be different between acceleration and decceleration.



The term locking is used when you have 100% enagement all the time, [or most all the time]. I have this in my classic car and the inside tire chirps when I turn.

i don't know of any way to tell visually

I posed that question to Mr. Guard when my GT was installed and he said no. There's no way to check a GT without applying torque. The more torque that's applied the more it engages. Mine hooks up better now in turns and full acceleration.

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[Harvey]

[quote name='flash' date='Mar 1 2006, 02:07 PM']yes - a GT torsen unit - sorry



i don't know of any way to tell visually, but there might be - that's one for bobby - he'd know better than anyone

[right][post="16793"]<{POST_SNAPBACK}>[/post][/right][/quote]



So...if I put my rear tires in a sandy spot and drop the clutch and spin out onto the pavement...and measure black tire streaks...shouldn't this be a kind of visual indicator other than eyeballing at the transaxle..which apparently doesn't tell you anything?



On the track in my 928 I know that when I gun it in a corner and it unloads one side, that side smokes and the other doesn't...no LSD. Not good. It's the one think IK don't like about that car.



Harvey

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