AWD malfunctioning ?

I got my car stuck last night, in a shallow ditch filled with ice/snow from the recent winter storm. Living in N.Carolina, I'm not the most experienced winter driver, but we've had more than our share recently, so I'm not a total novice either. Anyhow, it simply did not seem to me like my car should have been stuck (I should have just been able to drive out of the ditch). A former Subaru owner who was present had the same feeling.

I'm wondering if maybe my AWD system is malfunctioning - like maybe the thing is simply behaving as a FWD car. We noticed that the front wheels were spinning but at least one of the rear wheels seemed to be doing nothing.

So, two questions:

(1) is there a simple way to verify that the AWD system is functioning properly ?

(2) is there a simple fault that can cause it to malfunction ?

Thanks, John

Reply to
John Eyles
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If you had one front wheel and one back wheel spinning, the AWD was working.

Reply to
Jim Stewart

What he said. Only some Subes have an limited-slip differential at either end. An STi would have spun all 4 tires. Forester XS should spin 3. A VDC Outback should have applied the brakes to the spinning wheels, diverting power to the others. Speaking of which, applying the brakes with your foot can help in that situation too. Not nearly as good as a VDC setup, but sometimes it works.

Reply to
David

FYI my USDM 04 STi will only spin three with the DCCD in "LOCK" position. Both rears, and the right front. This is logical since it carried only the driver (me) at the time. This is on relatively flat, dry packed sand/dirt, from a standing start.

As I recall the front and rear diff are of different design. I believe the rear is a clutch type and the front is a gear type, but I am not positive about this. I do not know how the center diff slip is limited other than electromagnetism is involved, or to what degree it actually "locks."

I did not do an immediate followup test with the DCCD in minimum position. However when drifting on pavement it seems make no difference how it is set

Finally to reiterate, to test your AWD, stop on a flat, low traction surface, preferably dirt, and nail the gas for less than a car length of motion. If in dirt it should be easy to tell what happened by the tracks.

Reply to
John Emdall

of course, this tells you nothing of the limited slip characteristics of your differentials. that test is a bit more difficult (but not impossible).

ken gilbert

Reply to
Ken Gilbert

What Subaru? For most models/years, what you describe is normal. The front and rear differentials are open; that is if one wheel has to traction, the other wheel as no power (same torque = 0). Only the center differentials are locking/limited slip. So at least one of the axels needs to have traction on both wheels.

Some high-end Imprezas or Outbacks have a limited slip diff on either the front or rear axel, that would have helped you in this situation.

cheers!

Reply to
Dominic Richens

Sorry, it is a 1997 Legacy Outback 5-speed.

Ok, I can believe that maybe there was no traction on at least one wheel per axle. Guess I've gotten a little complacent, the thing has always been so amazing in the snow ! Also, my tires (Bridgestone Turanzas) have 60K miles and need replacement soon, so that is undoubtably contributing to the problem.

I do not have a clue as to whether I have that.

Thanks, John

Reply to
John Eyles

I'm guessing US model from your email, and I doubt very much you do.

60k miles on all season tires sounds like the real problem though. Powering another rear wheel won't help if it doesn't have any traction either. I think you can buy an LS rear diff to retrofit for ~US$1000 new (less from a junkyard), but I'd expect money on tires to be better spent.
Reply to
David

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