so I was dropping the girlfriend off at water polo practice and from a hill into a little driveway that was barely inclined. I stop to put it in first, and when I start going again my front left wheel is just spinning.

Whats up with this? How are these cars supposed to perform in the snow if they can't handle a driveway?? I had to roll back a bit to the main road to get it to go up, could there be something wrong?

 

Were you flooring it? I have driven up steep *** muddy hills without any problems

 

thats what open difs do its supposed to do that

 

The center should lock in that case. There still might be enough torque to the front to spin them, but your rears should pick up most of the load. You sure the rears weren't spinning too?

 

Yeah aren't the rears suppossed to get all the power unless they're losing grip too?

 

the front left only...my girlfriend got out and looked...i would think if all 4 had power my car would have moved anyways
maybe somethings wrong w/ the center diff??

 

you have an open diff up front, and one in the center, and you act suprised??

plus your uphill wheel will also tend to spin in these situations...

you center diff is locked 50/50 though, for all those that foolishly maintained that the rears kick in harder than the fronts...well lol

 

I have been on wet hills in San Francisco and deliberately got all four wheels spinning. I accomplished this in my Cobb Stage 2 sedan by reving it up and dropping clutch. All tires broke loose but this effect didn't last long and off I went. I shot up that hill.

 

GroupB you just said the center diff is open and then you said it is locked. Make up your mind.

On a 5MT WRX it is a viscous coupling locking diff. It's open until the slip (difference between front and rear axle speeds) reaches a certain point, and then it locks. At least it is supposed to...

 

if the center diff is locked 50/50, which I thought it was, then the front wheel should NOT spin by itslef.
I've only had this happen once when I noticed a wheel spinning in the exact same situation: turning right from an uphill into another uphill driveway. I've also intentionally tried to get the wheels spinning on wet days, and, even around a turn, flooring it in 1st, I can't get ANY wheelspin.

 

Uh...if the center diff is locked at 50/50, that means 50% of the power goes to the front and 50 to the rear. Which means that the front CAN spin...it's still getting 50% of the power.

 

MVWRX, differentials don't work like that.
They don't split "power".

An open diff (with no clutch or locking device) gives a 50/50 torque distribution. The torque on each output will be the same, but both outputs are free to rotate at different speeds. The constraints are:
output1 speed + output2 speed = 2 times input speed
output1 torque = output2 torque = 1/2 input torque
Power is torque times speed, so with the open diff, the power distribution will depend on the speed of each output, and it will only be 50/50 when both output speeds are identical.

A fully locked diff (locking device or clutch fully engaged, or no diff at all aka "spool") makes both outputs rotate at the same speed, but the torque on each output is now able to vary. The constraints here are:
output1 torque plus output2 torque = input torque
output1 speed = output2 speed = input speed
In this case the torque on each output will depend on the available traction, giving a variable "torque split" anywhere between 0 and 100 on each output. And because both output speeds are equal, the power distribution will be the same as the torque distribution.

What the WRX has (according to Subaru at least, I've never taken it apart) is a self locking center differential. It's an open diff until the difference between output1 speed and output2 speed grows beyond a certain point, and then the viscous coupling engages and it becomes a locked diff.

As long as both the fronts and rears have enough traction, it is a 50/50 torque split. Once either front or rear loses traction, the that output will speed up relative to the other ouput, the coupling will engage, and we get a variable torque split, with most of the torque going to the output with most traction.

I think the big question is whether the coupling engages fully, or does it slip a little? Also, assuming it engages fully, how soon does it disengage once the slip has stopped? I have no @#$#@ idea.

 

Thanks for the info Funked, it's good to know stuff like that. So in this case, the front wheel shouldn't have spun then right? I wonder what was going on...

 

I think it should have spun briefly and then hooked up as the diff locked. Maybe the locking mechanism is not as good as I think, or could be a mechanical problem.

I have a 5MT WRX too, but it never snows here, so I don't have much to compare it to.

 

Another thing, because the front diff is open, when the center diff locks, and one of the front wheels lost traction, you would get both rear wheels spinning at roughly the same speed, one front wheel spinning at twice that speed, and one front wheel stopped. That one front wheel spinning would be making most of the noise and vibration and "feel" of a wheel spinning, so you might not notice that the rears were spinning too.