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Old 04-15-2009, 04:37 PM   #1
g_man80
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Default '99 Forester Auto: Long delay before driving rear wheels

This seems like the most appropriate forum for this, but if not, mod's feel free to move:

This winter it has become pretty noticable. On slippery surfaces (snow, ice, etc) my wife's Forester, automatic w/ approx 135,000 miles, seems to allow the front wheels to slip/spin for 1 to 5 seconds before any power is sent to the rear. Mostly only noticable from a stop. When power is transferred it's pretty sudden/jarring. Almost like a neutral drop. It doesn't happen every time. From a roll the AWD is pretty seemless. I would say it happens usually just at the beginning of the drive. I understand that the setup in her auto Forester is fwd before awd kicks in, but it seems very slow to transfer power. The delay is enough thats it's similar, time wise, to detecting rwd slippage in an suv/truck and grabbing 4wd manually. This seems pretty excessive to me. Is this just an age/high mileage thing, or is there a problem?

Thanks from MT where we are still snow covered.
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Old 04-15-2009, 05:04 PM   #2
Patrick Olsen
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My father's auto Outback had a similar problem. It has something to do with the electronically-controlled center diff clutch pack. I honestly don't remember what he had to have done to resolve it - I think it was a complete tranny swap out (under warranty, in his case).

Perhaps others can chime in with more definitive information.

Pat Olsen
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Old 04-16-2009, 12:16 AM   #3
SilverBullet2.5RS
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From: http://www.rs25.com/forums/showthread.php?t=99075


"You say "I've got a Subaru - it's full-time AWD already - the TV told me so, and the car has a sticker that says AWD!"
Well, ok, but not really - it depends on what transmission you have. If you've got the 5-speed manual (5MT) you've got the closest thing to a full time 50/50 torque split. If you got extra lucky and have one of the 00+ RS's you've got a rear LSD as well, so you're all set - you can stop reading if you want.

If on the other hand, you have the pre 02, 4-speed automatic (4EAT), you're not so lucky. Your torque split can vary from 50/50 to a 90/10 front-bias.
The Transmission Control Module (TCM) on the 4EAT tries to intelligently divide the torque based on conditions, and for most situations it does just fine. However, it's practically worthless for precise, low traction driving. It has a 90/10 (F / R) torque split in most forward gears, calls for shifts at all the wrong times, and the overall gearing is poorly suited to manual shifting. Don't even get me started on the stupid shift gate that prevents hassle free 2-1 downshifting. If you ever rallycross your 4EAT, or go for a brisk drive on snowy, muddy, or gravel roads, you'll quickly learn that the time it takes for the TCM to react is precious time.

Since the default bias is 90/10 you're effectively driving a FWD car. When you lose traction, the car understeers (pushes) to the outside of the corner where bad things like curbs/ditches/mailboxes/guardrails, live. Eventually the TCM reacts and transfers some power to the rear wheels, but by then, you've either gotten past the issue, or it's entirely too late."
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Old 04-16-2009, 10:55 AM   #4
g_man80
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Thanks for the link SilverBullet. I was aware of the default front bias split in her Forester, but I felt that the multiple second delay followed by a jarring trasfer of power wasn't quite right. Maybe it's just the nature of the setup: sometimes it guesses right and reacts quickly, other time it's confused and has a noticable delay. FWIW, I had an '02 5spd wrx a few years back and can attest to the crazy fun the 50/50 setup offers .
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Old 12-10-2009, 02:24 AM   #5
Jkm3141
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I have had the exact same complaint about my 99 Impreza sport wagon automatic. My friend owned an early model Impreza automatic with about 205K miles on it, and it is the car that made me fall in love with AWD. It has a perfectly seemly transition from FWD to AWD.

However, my 99 impreza has never had that same feeling. It always has TERRIBLE understeer when turning in snow, with a long delay and a clunk when the rear wheels engage. From then on the car feels just like my friends Impreza with 50/50 division of power. However, after I let off the gas to cruise, the whole process repeats as the transmission goes back to 90/10. Is this simply because the centre differential clutch packs are worn out on my transmission? Could it be that I need a transmission fluid change? I have never heard or felt the rear diff clunk when not driving in snow. The lag in power delivery happens on dry pavement as well, however is way less noticeable as there isn't as noticeable a clunk. I am only confused because I have witnessed how well AWD can be on a 4EAT, and am wondering why my Impreza can't.

- John
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Old 12-10-2009, 03:37 PM   #6
iluvdrt
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I know the Duty Solinoid C controlls the center diff. Maybe yours is going bad and it isnt telling the center diff to x-fer the power. The solinoid is easy to change, but I cannot remember where it is.

This is also the same solinoid that causes torque bind.
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