Limited slip rear differential

If you do in fact have a rear LSD, you are correct that both wheels should be spinning. You may want to contact your dealer to verify that you have one.

Limited slip rear is standard on WRX. A limited slip is exactly what the name implies. If you put the car in a condition where it thinks you are cornering the diff will allow one tire to get all the power. That is why in snow and mud often you will get stuck in the situation you describe and is also why people that offroad prefer some type of locked diff to a limited slip one. There is also a possibility that it has broken in some way but what you describe is considered normal behavior for a limited slip driven in snow or mud.

Jason Kavanaugh

A limited slip will spin only one wheel at times, just not as easily as an open diff. More preload will help if you want something closer to a locker...I would. TG

how did you notice one back wheel was spinning? was there someone else driving the car, or watching it?

the viscous coupling at the rear of the rex is a somewhat "weak" unit, in that it takes quite a bit of angular velocity differential to cause the unit to begin stiffening. in other words, expect a decent amount of wheelspin before the LSD action kicks in.

how much did you spin the wheels?

ken

differential

Hey Ken,

Yes, there was someone else driving the car so that I could analyze the situation.

I think that there was a decent amount of wheelspin. To put numbers, the car was in first and revving at more than 4000 RPMs for a considerable amount of time.

Matt

I'm not sure how effective a viscous limited slip is. The factory service manual for my MY2002 Legacy doesn't say much about it.

It looks like your center diff. (which is also a viscous limited slip) performed as it should. I would assume the rear diff. is of similar design.

How do these fail, typically? Open or closed? If they failed open, most folks probably wouldn't notice.

It sounds like it has failed. I believe they almost always fail in open mode. In snow, it ought to have enough lock to spin both rear wheels. If not, it ain't gonna do a hell of a lot in the dry.

The rex is fitted with a plate type LSD in the rear. These are set with little or 'NO' preload in the road cars therefore they need to see some torque feedback for the ramps in the diff to 'lock the diff' with a car beached on snow there is very little torque feedback to the diff. hence no locking action. it is likely that even with some more preload, (as the rally cars are set) there would still no have been enough traction in this situation to drive you out.

John G

john,

not the rexes sold in north america. these have the vc type units in the rear diff.

ken

Therfore, do we agree that there is a problem with my LSD.

Matt

Maybe, although a viscous type is not likely to completely lock up in this sort of situation. LSDs are really more for low traction conditions, not for getting unstuck. You want a locking differential for that, which is a completely different beast...

I suspect there's nothing wrong with your car.

The viscous diff should have enough lock to spin both rear wheels if they are on snow. It sounds like it has a problem.

Would'nt you call having both wheels in the air a low traction condition!?