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Identifying a viscous LSD versus helical versus clutch-cone

Old 06-10-12, 05:01 AM
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Identifying a viscous LSD versus helical versus clutch-cone

I know in general you can tell if a car has a functioning LSD if you spin one wheel and they spin in the same direction, but is there a way to tell what kind of LSD a car has without actually taking it apart?

I'm pretty sure my MR-2 has a stock viscous, but what I move the wheels back and forth it has just a little bit of play, and makes a very slight clank, clank sound. If an LSD is viscous, wouldn't it not make much noise? I figure a Torsen wouldn't make much noise either...

I also noticed this winter that when I got stuck in the snow, one tire would spin and the other tire would just sit there unless I floored it... which was very frustrating. Having a locking diff would have helped a lot...

But I wonder if maybe my car has an aftermarket diff that's simply totally worn out. Probably not, though.

I would be really annoyed if I spent money on a new LSD to find out when the transmission is popped open that I could have just got a $150 rebuild kit. lol.
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Old 06-11-12, 01:02 PM
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pull the axles. if it's viscous 1 should have a longer shaft that goes into the diff. I think they also have a different number of splines.

go onto some mr2 forums like mr2oc.com or toyotanation. there are probably a bunch of others. they'll be more knowledgeable than us.

what gen MR2 is it?
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Old 06-11-12, 05:33 PM
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I don't want to pull anything apart. I just wanted to know if there was a way to tell each type of LSD apart just by sound and feel.

Generally an aftermarket clutch type will make noise and you will feel it clicking through tight turns, and when you turn the wheels it takes a certain amount of force for them to turn apart.

No idea how torsen and viscous feel though...
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Old 06-11-12, 06:17 PM
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The MR2 viscous diff centre have been used in motorcycle powered cars over here. They never seemed to last long in that application, let alone in a car, but can't remember hearing anything on clanking.

IIRC they were fitted standard to the supercharged model. If you did take a look, they were about 7~8" diameter, 2~2 1/2" wide chunk of cast iron about 8kg bare of crownwheel.

I wouldn't place much faith in any of the jacking/spinning wheels tests as good for seeing if there's an LSD there. Aside from clapped out ones open wheeling , older F3 dallaras fitted with torsens have virtually zero lock up, old ZF salisbury types wouldn't either when new.
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Old 06-11-12, 06:22 PM
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It's an SW not an AW. 3S-GTE not 4AG.

So torsen and helicals can't be identified by spinning or torquing the wheels?

My diff has a little bit of slop, which is what causes the slight clank noise when turned back and forth. Probably from being viscous. Clutch types don't have any slop AFAIK.

And if it was a worn out clutch type it would have gotten really noisy.
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Old 06-11-12, 11:31 PM
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with older torsens, the wheels will spin opposite directions like an open diff. they suck in snow, but work great in other conditions. they just need some resistance on the unloaded wheel. if your wheels spin opposite, but leave two black burnout marks, its probably a torsen.
updated torsens (late 90's up usually) spin the same direction because they are preloaded to prevent the above problems.

viscous and clutch will spin the same direction. no idea how to tell them apart other than visual inspection.

torsens dont wear out, they just break. viscous/clutch just turn into opens when they wear out. they may lock up and cause low speed chatter, but thats usually from internal damage like overheating, not age.

the play you feel when you move the wheel is not the diff. its either excess backlash in the ring gear, or play in the CV joints.
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