Differential question.

[Tiamat-red]

I'm new to AWD cars and I had a question. I just bought a 92 LS-L and noticed I could rotate the back wheels with the front's still on the ground.
Is this normal?

[UberRoo]

Yes, that's normal. The transmission computer doesn't engage the AWD until it thinks you need it. If you've got the rear end up on jack stands, I guess you probably don't need it.

Basically it has sensors in the front and one in the rear that measure wheel speed. If the front wheel speed is higher than the rear, it locks up the center "differential" and sends you on your way.....however, SVXs don't have a center differential. It's just a clutch. When you don't need AWD, it's disengaged.

Having an actual differential could in some ways be a better design, but the clutch method actually works amazingly well. It probably works better than a center differential that doesn't have limited slip capabilities because it can actually lock things up completely instead of only being able to distribute a fixed amount of torque. The newer Subarus use a combination of an actual differential and a clutch.

[Tiamat-red]

Good! Thanks!

[Tiamat-red]

Oh, wait.
Is any of this controlled by the same sensors as the ABS? Like on some traction controlled cars? Because my ABS light is on and presumably not working. I know how to do the diagnosis but haven't yet. Since my Air bag light is also on and I've made that a priority.

[UberRoo]

I don't know if they're the same sensors. I would think they are because I've never stumbled across any information about the ABS sensors, however, I have been led to understand that the antilock is a four-channel system, meaning that there should be four wheel speed sensors. The transmission only has three. Despite this discrepancy, I think the ABS is not truly four-channel, and they are the same sensors. ...but I don't know, and I'm just speculating at this point.

The tests are really simple. Romp on your brakes. If the wheels skid, the ABS isn't working. Next, put your rear wheels on something with good traction, like asphalt, and the front wheels on something with poor traction, like wet grass. Romp on the other pedal (the gas) and if the car takes off without shooting wet grass everywhere, the AWD sensors are probably working.

Be gentle doing these tests. Don't break your car.

[oab_au]

Originally posted by UberRoo
.

Having an actual differential could in some ways be a better design, but the clutch method actually works amazingly well. It probably works better than a center differential that doesn't have limited slip capabilities because it can actually lock things up completely instead of only being able to distribute a fixed amount of torque. The newer Subarus use a combination of an actual differential and a clutch.

The diff used in the Euro version uses a hydraulicly controlled Limited Slip Clutch. If front or rear wheels slip, it tightens up, and can lock the transmission into 4WD.

Harvey.

There are front and rear inductive pickup sensors inside the tranny to compare front revs to rear revs. Not hooked to ABS for traction control.

You can see the rear sensor on the rear of the transfer case it is at the 3 o'clock position.

-S

[UberRoo]

Where does the ABS get it's signal from? I know Subaru decentralized the control modules quite a bit, but I know they share a lot of data.