Last post on Aug 29, 2010 at 9:02 PM
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Subaru Forester, Transmission
#133 of 182 Re: Question about all-wheel drive system??? [aceonthebeach3]
Feb 15, 2008 (10:28 am)
Basically, the viscous coupling acts as the center differential. When the axles spin at different speeds, the fluid-filled coupling heats up and the fluid thickens and locks the axles together temporarily.
The AT uses what they call Auto AWD, basically electronically controlled variable transfer clutches. Simple yet effective.
Here is a cool video - you see a basic Forester X auto having no trouble transferring power from axle to axle, front to rear and rear to front. Note how little wheelspin there is on the Forester:
Both systems are very capable.
The 2009 models adds traction/stability control, so it will only improve.
#134 of 182 Re: Question about all-wheel drive system??? [aceonthebeach3]
Feb 15, 2008 (4:15 pm)
"... could someone explain the difference in the auto All-wheel drive and the stick shift all-wheel drive system?"
Here are some bits and pieces I have picked up about Forester drive trains:
The X Sports model (either manual or auto) and the LL Bean model (comes auto only) have X model drive trains.
All the Forester drive trains have viscous limited slip rear differentials.
The printed catalog lists the drive trains as follows:
Manual X and XT = Continuous AWD:
Viscous locking center differential and limited slip rear differential.
Automatic X = Active AWD:
Electronically controlled variable multiplate transfer clutch and viscous limited slip rear differential.
Automatic XT = VDC (engine management and traction control system) and VTD (Variable Torque Distribution) AWD:
Electronically controlled variable multiplate transfer clutch, planetary center differential, and viscous limited slip rear differential.
If you have the automatic transmission, power in Drive and 3rd is biased 80/20 toward the front. There is 50/50 power distribution front and rear if you place the selector lever in 2nd or 1st. If you have a manual transmission the split is 50/50 in all gears.
If you have Limited Slip Differential (optional in non-X models, standard in XT models), you'll have at least three of four wheels available. If you don't, you could have two wheels of four available, one front and one rear.
No forester in the US has a front LSD unfortunately (apparently only the forester STI ever got one). The nonvdc foresters have a front open diff with a clutch pack in the center of the car to distribute power f-r and either an open rear diff in the X model or viscous limited slip in the rear on XS and XT models. The forester vlsd is very loose though. A US Forester will act the same as any awd or 4wd that has open diffs. A non-Rubicon Jeep Wrangler will do the exact same thing. You will always have at least 2 wheels spinning, and you can drive through the brakes to get power to transfer.
#135 of 182 Re: Question about all-wheel drive system??? [aatherton]
Feb 15, 2008 (6:34 pm)
Another bit of info just copied:
In the non-X models, when there are LSDs, both automatic and manual models use the rear mechanical LSD. The difference comes at the fore/aft transfer case... Automatic goes electronic (the E in 4EAT) and while in 4 or 3 shifter location, varies the ratio from 80/20 to 50/50 based on "sensed need".
When shifter location is in 2 or 1, the 4EAT locks the center differential at 50/50 power distribution.
When shifter location is in 2, the 4EAT locks second gear. First gear can't be accessed while shifter is in 2, so take-offs are in second gear. Sounds stupid on pavement, but in wintry locations, where snow and ice are common, it seems a lot smarter.
Why are 3 and 4 different from 1 and 2? For reasons of economy having power distributed mostly up front makes a lot of gas mileage sense, with power only going to front pair...plus by the time you're in third and fourth gears, you shouldn't be having traction problems (certainly possible with turbo models, but not advisable in normal use...ie, above speed limit). Wonder why the automatic has traditionally gotten better mileage than the manual? ...it's the E in 4EAT.
Feb 15, 2008 (7:23 pm)
thanks everyone for your help. i think the XT trim sounds like it is the best.
#137 of 182 Re: thanks [aceonthebeach3]
Feb 16, 2008 (3:33 pm)
Which trim? The XT is fabric, with a slightly better seat fabric than the X. The XT Limited is leather. But to get a turbo just because of better seat fabric does not make sense, so it must be the leather trim of the XT Limited that you like best. But if leather is best, you can get it without the turbo in the LL Bean. Unless you want a manual transmission, which is not offered in the LL Bean, so you are back to the XT Limited.
#138 of 182 Re: Question about all-wheel drive system??? [aatherton]
Feb 19, 2008 (10:03 am)
Check out the video, though.
When they say 50/50, I wonder if they mean the power split, or the fact that axles are locked somehow.
In the video, notice the front axles doesn't spin at all when it's on rollers. The rear axle also does not spin when it's on rollers.
If the front axle were actually getting 50% of the power at a minimum, they would be spinning like mad. Yet they remain still, implying zero power to that axle. Remember there was no traction control on that model (2006-7 X automatic).
Theory is great, but in practice, that front axle gets no power at all, hence it does not spin when it's on rollers.
Suffice it to say, it just works.
Feb 20, 2008 (12:55 pm)
I want turbo, and I want leather. I always have dealers do aftermarket leather. it saves me money. I will do a XT auto and add aftermarket leather
#140 of 182 Re: '07 Forester - Noise while accelerating [erik9]
May 05, 2008 (9:26 am)
I have 2009 forester 2.5 X w/ premium and a day later i started to hear a "rolling noise" from the fron drivers side.. I took back to dealer & they suggested I change tires. (road noise). Called yokohama & they replaced N/C . I put on Avid H4S yokohama and same noise still there. I'm not sure this is the same noise as you're having. Started a case with SOA and subaru rep will look at car on 5/12. test drove another 2009 forester and same noise but les evident. Dealer also confirmed same after driving another vehicle. I love the car but hate this noise. Hoping for a resolve. Dealer said bearing were ok. Maybe axe. who knows.
#141 of 182 Re: '07 Forester - Noise while accelerating [firstsub]
May 05, 2008 (10:46 am)
I thought bearings, too, they're OK, eh?
Drive in a figure 8 in an empty parking lot. See if that does anything. This is advice SoA techs shared with us in the past.
#142 of 182 Re: '07 Forester - Noise while accelerating [ateixeira]
May 05, 2008 (1:00 pm)
Good to know as I am hearing some different, odd rumbling sounds from vehicle that show up at higher speeds. When I get chance I will try figure 8 in our lot to better understand.
Then again, it could be because our roads have been dry lately, and most of my driving up to now has been on wet roads/in rainy weather.