front wheel, rear wheel bias

[scottzg]

does anyone know the power distribution between the front and rear wheels on these things? I know the automatics are pretty much fwd, what about the manuals?

[vrg3]

The automatics aren't pretty much FWD all the time. They're pretty much FWD on light cruise, but the multiplate transfer clutch can and does fully lock up when necessary, giving each axle as much torque as it can handle. The manuals use a mechanical center differential with a viscous coupling that also fully locks up under slipping conditions.

In short, the automatics start off with a heavy front bias which tapers away towards neutrality when wheelspin or hard acceleration happens (or any other time the computer feels the need), while the manuals maintain a neutral split at all times.

[Legacy777]

The "official" numbers are

For the auto under normal cruising/driving 90/10

For the manual under normal crusing/driving 50/50


and just for the hell of it....the new VTD auto trannies found in the WRX and newer legacies have 45/55 under normal cruising/driving.

[ciper]

I dont like the misconseption about how the Auto AWD works. 10% doesnt mean the rear wheels are being dragged around. It means they ARE powered, the clutches ARE engauged, the rear wheels ARE pushing the vehicle through a turn. From the instant that a difference in speed occurs until the TCU increases pressure the rears will only be powered at 10%. If the rears have a large enough difference in traction the car could sit and spin. Even trying to induce this situation isnt easy, it rarely occurs during normal operation.

When such a large traction difference is present the "slip" time is very small. This can be tested by stopping the front wheels in a drainage dip and the rear wheels on pavement. Practicing your launch you can get the car to spin for a split second, afterwards the car moves well.

The current* 5 speed is far worse. The Viscious center will Never transmit 50% of the power to the higher traction wheels under a slip condition. What is worse is that since the differential is open the wheel loosing traction has to sping over 2 times as fast as the others!!! Most often this means that one front wheel will smoke itself to high heaven while the rears barely push you along in an agressive turn. This is with a low mileage center diff. Imagine if yours has some wear.

Search around and you will find many involved in motorsports with 5 Speed subaru complain about "lightin up the inside wheel" on turns. Id much rather have a locking or truely variable torque distribution.

Sure you can use the STI center differential, and install front and rear LSD but just coming from a stock situation the auto clearly has an advantage in either our form or in VTD.

*Current 5 speed as in non locking center differential like in non Legacy/Impreza vehicles.

[vrg3]

Yeah, the auto AWD system is a kind of mysterious thing. 10% means that the clutch is 10% engaged -- whatever meaning you attribute to that. So the power is being sent to the rear. And, like you say, the instant more lockup is needed, the TCU delivers it. In theory there's a small delay, but like you say you'd never notice it in real life.

I'm not sure I understand what you're saying about the "current 5 speed." The one thats in "non Legacy/Impreza vehicles?" You mean the 5-speed they put in Foresters? Or what? Aren't they all the same?

I don't know that much about how the 5MT changed in 2002, so I can't speak directly to that point, but the 5MT that is in our cars with the viscous coupling does indeed fully lock up in a slip condition. Note that in a situation where (for example) the rear wheels are slipping and the front wheels are not, it's impossible to send any meaningful torque to the rear. A fully locked center differential in that case would send nearly all the engine's torque to the front. An unlocked open center diff would send almost no torque to either one.

Even with a good center differential, it's still possible to light up the inside wheel on a turn if your front and/or rear differential is open, like most of ours are.

Is the "current 5 speed" you speak of not based on a standard-ish viscous coupling LSD?

[Legacy777]

The 5 spd is pretty much the same as it always has been.....same AWD system, same center dif with viscous coupling.

[totech]

I second ciper's observation of "smoking inside front wheel on 5Spd"

One of the guys up here, has that very problem in his Legacy!

Or - my binding auto - probably 50/50 locked - the best solution... Until time to park!

[scottzg]

i was under the impression that the manual had clutch type differentials and only the auto had the viscous center diff.

[ciper]

Current as in not a GL DL Loyale XT etc... Jeese! Many AwD versions have existed like locking center differential and dual range. Remember too that the Loyally was available in 94, justy was available in 94 and the xt was available in 91

VRG3: It does not fully lock on slip. Even if you take the center differential to a point of overheating it never comes anywhere NEAR fully locked.


Scottzg: You have that all twisted around sideways and barckwards
The 5 speed has a center viscous differential while the Non-VTD automatic has a setup similar to a motorcycle clutch that is hydrolicly driven and controled by the computer.

[czo79]

My experience with post 1990 subaru automatic AWD is limited to a 99 forester S, although I have to admit, it could have been a 2000. I have spent a lot more time in manual subarus. I always have found the 5spd to handle so much better. I also like 5spds for the control they give me. But when it comes to handling, the 5spd seems so much more predictable and controllable. I guess probably because it is simpler, with the 50/50 power split and such. I find I have such great control over the rear end. I remember so many times going 30-50 straight down a road, doing 180's back and forth over and over nonstop, yet still going straight down the road...this was low traction conditions of course. It always felt like I couldn't trust the 4EAT when I started drifting and sliding and such. It seemed like their was a slight delay before power got where it was needed, and felt like the computer was moving power around the wheels, but it wasn't predictable, you couldn't tell how the car would react. I just couldn't feel comfortable pushing it. Oh hell, I can't explain this. I have been trying, but I can't find the right words. Hopefully you all get my point. It reminds me of an article I read on the H6 VDC outback. They compared a whole bunch of AWD wagons in the snow, they had a set course up, and the VDC was the slowest by such a huge margin, cause it wouldn't allow wheelspin/slippage/drift at all. I recognize that 4EAT and VDC and all these auto systems are more technically advanced and will maybe get you unstuck from the mud better or whatever, but they don't seem fast, they don't inspire confidence when driving 80 down a snow covered one lane dirt road or whatever...
My rather ignorant 0.02$
Thanks
Micum

[submannz]

This changes quite a lot between years models and Impreza's and Legacy's