01 Forester LSD/AWD

[upnorthguy]

I'm messing around with the '01 Fozzy I got last summer.  I'm not convinced the AWD is working correctly as the front wheels seem to spin easier than I think when starting out in some slop (not a ton of snow yet, so I haven't had the best conditions to test).

 

I found a few threads (including this one) about testing AWD, but I'm wondering if that applies to my rig.  This one is the S model with, I think, the LSD in the rear.  I have it on jack stands and when placed in drive, the front wheels spin and the rears sit there like slugs with no rotation.

 

Transmission number is TZ1A3ZC2AA-P8.  Am I looking at a bad VC, center diff or something else?

 

Thanks!

 

 

[Fairtax4me]

There's no VC or center diff in the auto trans. Rear drive power is transferred via a clutch pack in the tail of the transmission.

 

The auto trans has speed sensors for the front and rear outputs and compares those to detect slippage of the front output. If too much slippage occurs the rear drive transfer clutches are given higher fluid pressure by the C duty solenoid to give more drive power to the rear driveshaft.

It should also react to throttle input. Heavy throttle should cause the duty C to lock down the transfer clutches and give drive power to the rear driveshaft. With the car on 4 jack stands you should get the rear wheels to spin by giving it throttle. Rev the engine up some and see if the rear wheels engage and spin with the fronts. You may get an ABS or TCS light blinking because often the wheels will be spinning at different speeds and will cause the ABS control module to think the wheel speed sensors are faulty.

If rear drive engagement is delayed it could be because of low fluid pressure to the transfer clutch pack or C duty solenoid. Or it could be due to excessive clearance between the discs in the clutch pack.

 

And just for clarification, no action of the duty C solenoid or rear drive will ever affect the front drive components. The front wheels are driven 100% at all times.

Edited December 3, 2016 by Fairtax4me

[upnorthguy]

Ah, that helps explain why my ABS light was on (but has subsequently gone out).

 

Of course I had packed up the stands and moved on to some other projects.

 

Rejacked/standed and tested.  Throttle increase does cause rear wheels to spin.  

 

I guess the spin I feel at the front wheels is the initial slip before the rears have kicked in as the throttle increases.  Seems like this feels different compared to the 95 EJ22 I had (I don't recall it having the same amount of front wheel slip during a slippery start from zero).  Maybe a little more torque/HP with the EJ25 causes that?

 

Thanks for the clarification on my misunderstanding of VC/center diff (or lack thereof) on the AT.

Edited December 3, 2016 by upnorthguy

[Fairtax4me]

Sometime in the mid 2000s they changed the way the duty C solenoid works, which was supposed to help increase the life of the transfer clutch pack, but it also means there's a bit of a delay in the AWD engagement. I wanna say that was around 04 though.

 

As I said above, a delay in engagement of the AWD could be for several reasons.

 

If the transmission fluid is old you might try changing that and the external spin-on filter. Be sure to get a real Subaru filter.

[DaveT]

This sounds like why I never liked how our 01 drove in snow. I much prefer my older ones that have part time 4wd.

[upnorthguy]

I already did a 3x fluid swap.  I did not replace the spin on filter, though.  Maybe I'll think about that next summer.

Thanks!