Limited slip rear differential

[Joe Blow]

Hi,



I have a 2003 WRX (5MT). The other day I was stuck in deep hard snow.
There was no weight on the wheels, I was really stuck. Therefore the wheels
were spinning without any effect.



To my surprise, I noticed that only the front right wheel and the back
left wheel were spinning. How come only one wheel was spinning at the back?
I thought since I have a limited slip rear differential, the differential
should lock when one wheel spins faster than the other one. Therefore, both
back wheels should be spinning.



Thanks,



Matt

 

[Rob Munach]

Hi,



I have a 2003 WRX (5MT). The other day I was stuck in deep hard snow.
There was no weight on the wheels, I was really stuck. Therefore the wheels
were spinning without any effect.



To my surprise, I noticed that only the front right wheel and the back
left wheel were spinning. How come only one wheel was spinning at the back?
I thought since I have a limited slip rear differential, the differential
should lock when one wheel spins faster than the other one. Therefore, both
back wheels should be spinning.



Thanks,



Matt

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.

 

[Jason Kavanaugh]

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

 

[TG]

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

 

[Ken Gilbert]

Hi,



I have a 2003 WRX (5MT). The other day I was stuck in deep hard snow.
There was no weight on the wheels, I was really stuck. Therefore the wheels
were spinning without any effect.



To my surprise, I noticed that only the front right wheel and the back
left wheel were spinning. How come only one wheel was spinning at the back?
I thought since I have a limited slip rear differential, the differential
should lock when one wheel spins faster than the other one. Therefore, both
back wheels should be spinning.



Thanks,



Matt

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

 

[Joe Blow]

"Joe Blow" <(e-mail address removed)> wrote in message

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

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

 

[Verbs Under My Gel]

Hi,



I have a 2003 WRX (5MT). The other day I was stuck in deep hard snow.
There was no weight on the wheels, I was really stuck. Therefore the wheels
were spinning without any effect.



To my surprise, I noticed that only the front right wheel and the back
left wheel were spinning. How come only one wheel was spinning at the back?
I thought since I have a limited slip rear differential, the differential
should lock when one wheel spins faster than the other one. Therefore, both
back wheels should be spinning.



Thanks,



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.

 

[Rob Munach]

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.

 

[John G]

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

 

[Ken Gilbert]

The rex is fitted with a plate type LSD in the rear. These are set with

john,

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

ken

 

[Joe Blow]

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

Matt

 

[DH]

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.

 

[Rob Munach]

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.

 

[M Gibeault]

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