AWD Questions ???

[SubaruNewKid]

Okay, So I don't actually own an OB yet. I joined this forum to learn some stuff about the car because I'm looking to buy one. I have a few questions about the AWD. Like, How much power is given to the front, and the rear wheels. Is it 100% for both? And do you ever permanently disconnect the rearwheel drive, like on other AWD cars?
(PS: don't hate me for the thought of getting rid of AWD. I'm new to this and I just don't know)

Also, The OB I'm looking at is a '97. I've heard they're prone to over heating (replace headgasket) but are there any other common problems with this model?

I know you probably don't want to respond but please post some helpful comments. Thanks.

[AWDFTW]

AWD depends on the transmission. On the old 4 speed autos like that one it will be a continually variable ratio. Default is 90F/10R but is continually changing based on the computer's input.

You can put these cars into FWD mode in emergencies, but it will not help your MPG if that is what you're after. The weight is still there and the car is designed to run AWD.

Timing belt and assorted goodies are due at the 105k mile marker, this is an interference engine, so broken belt = fragged engine.

Tires need to match in wear and diameter, or your AWD system will start to hate life, expensively.

IF it has HG issues, on the 1996-1999 models look for internal leak signs: overheating, bubbles in the coolant tank etc. If it has been fixed, and the job was done right it should be good to go for a long time.

Basics: these cars like NGK plugs. Parts that need to say Subaru: sparkplug wires, thermostat (stants are crap for our cars),

Subaru Research Site- specs, prices, options, 2011, 2010, 2009.. Outback, Legacy, Forester, Impreza, Tribeca will help you research and the search feature here will help with anything else.

Also, welcome.

[rockhopjohn]

To add to AWDFTW comments, on all Manual transmission Outbacks (of any year) there is a 50/50 split front to rear all the time, that cannot be disengaged.

[SubaruNewKid]

Awesome, thanks. I'll check the coolant tank when I go to get the car.

[SubaruNewKid]

Originally Posted by rockhopjohn

To add to AWDFTW comments, on all Manual transmission Outbacks (of any year) there is a 50/50 split front to rear all the time, that cannot be disengaged.

Oh wow. Yeah, the car I have lined up is a '97 manual. So I guess 50/50 it is.

[SubaruNewKid]

Also, is $2000 resonable for a '97 manual? Or does the price sound suspicious?

[nyati13]

Originally Posted by SubaruNewKid

Oh wow. Yeah, the car I have lined up is a '97 manual. So I guess 50/50 it is.

The power splits being quoted are for dry non-slip conditions. All Subarus can push up to 100% of the power to the axle (front or rear) that still has traction.

[plain OM]

All Subarus can push up to 100% of the power to the axle (front or rear) that still has traction.

Depends on how you define 100% of the power.

If the AWD system, whether the viscose coupled center differential in the MT, or the multi-plate clutch in the 4-speed, 5-speed and CVT, is working properly, there should never be a 100% transfer to just the front or rear drive shaft.

The AWD systems work by monitoring, either mechanically or electronically, the front and rear drive shaft speeds and when a difference is detected, they operate to lock the two together, thereby assuring that they turn at the same speed. The MT does this by generating heat in the center viscose coupling, causing the internal fluid to change to a virtual solid, causing the opposing plates in the coupling to turn together. The AT does it by increasing hydraulic pressure on the MPT clutch.

Moreover, in the AT, it's impossible to have more power being transferred to the rear. In the AT, the front drive shaft is connected directly to the output shaft of the transmission -- it's always connected through the transmission to the engine. Only the rear drive shaft can be connected by a varying degree of friction developed in the MPT clutch, which is also driven by the transmission output shaft. When the MPT clutch is fully engaged, the rear driveshaft can turn only at the same speed as the front, not faster.

In the MT, it is possible that the center differential will momentarily allow the transfer of relatively more power to the rear if the rear is slipping (as happens with any open differential) but the viscose coupling will engage rapidly in any event and bring the two driveshafts into sync.

When on dry pavement, in the MT, both driveshafts are being driven from the same source and therefore, one could say, the system is splitting the power 50/50.

In the AT, the MPT clutch is varying constantly depending on speed, engine load, throttle position, etc. Even with the throttle off (5%), the hydraulic pressure on the clutch is about 30% of maximum. As soon as the throttle is advanced, this jumps up, and for most non-slip driving, the pressure will generally be above 50% (less when coasting, more when accelerating). So the rear wheels are always being driven. The normal gap between some pressure and 100% pressure on the clutch plates allows for some slippage which is necessary when turning corners and even when making slight course corrections while driving straight, because in these situations the driveshafts will not turn at the exact same rate. However, if the difference in driveshaft speeds and other sensor inputs are beyond a threshold the control module will assume slippage and maximize pressure on the clutch.

[awd-gg]

Originally Posted by plain OM

Moreover, in the AT, it's impossible to have more power being transferred to the rear. In the AT, the front drive shaft is connected directly to the output shaft of the transmission -- it's always connected through the transmission to the engine. Only the rear drive shaft can be connected by a varying degree of friction developed in the MPT clutch, which is also driven by the transmission output shaft. When the MPT clutch is fully engaged, the rear driveshaft can turn only at the same speed as the front, not faster.

I'm confused. Subaru claim that the 3.6R OB have a 55%rear:45%front power split...

[rockhopjohn]

Originally Posted by awd-gg

I'm confused. Subaru claim that the 3.6R OB have a 55%rear:45%front power split...

He's referring to the 4EAT that is in the 1st Gen Outback in question, not the 5EAT VTD system available in the 2005+ models.