From: "Edward Hayes" Subject: Re: Subaru Automatic AWD isn't really, in most models Date: Tuesday, October 21, 2003 2:45 PM
Subaru of America (tech dept) and Subaru of Australia claim that my 2000 Forester AUTOMATIC has a default ratio of 60 front/40 rear until wheel Torque difference is detected. The AT is almost always in a state of flux and is always activated unlike the locking center differential on the MT models. The 60/40 default ratio is fixed by the transfer gear set as shown in the Subaru Factory Manual. Power is transferred by a "continuously variable clutch pack" behind the transfer gear set in the transmission. The same gear set is reversed to obtain a default ratio of 40/60 for the Impresa GT ? To quote Subaru literature "to give a more sporting feel in spirited driving" I think the "old" Subarus that were front or all wheel drive depending on whether the system was activated may be where the 90/10 or
100/0 idea came from. The AT system even in the base Subaru is a far more advanced AWD system. In fact Subaru called it the thinking mans transmission for its almost instantaneous reaction to wheel torque compared to the locking differential which is locked until wheels slip and then the silicone oil heats and then power is transferred. Subaru factory racers have a switch to deactivate the locked center differential so as to bypass the much delayed power transfer. Let us get our facts in line before typing. I thought the normal automatics we 60:40 front:rear and could adjust to > 50:50 max rear
> The can also adjust to 95:5 front:rear.
>
> I found this info at
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in the shockwave animation>
> I do agree thought that it is not as good as the manual. But it is alot
> better than the CRV
>
>
>
> >
> > I've been spending a lot of time lately studying Subarus
> > and am starting to see clear through the misleading text
> > by Subaru and others on the subject of AWD and automatic
> > transmissions. Personally I drive a manual but I've been
> > so bothered by the incomprehensible descriptions of the
> > automatics that I wanted to find out what was really going
> > on.
> >
> > With manual transmissions there isn't much confusion.
> > Most if not all AWD manuals use three conventional
> > differentials : one to split the power front to back,
> > then one at each end to split the power side to side.
> >
> > There is usually something to block the center differential
> > so if one wheel spins power will get sent to the other
> > end of the car just the same. Most Subarus use a
> > viscous coupling in the center differential which locks
> > up if there's too much of a difference between front and
> > rear.
> >
> > My Corolla AWD wagon has an electrically lockable
> > center differential which is operated at the push of a
> > button (as does the current Subaru STi). A much better
> > idea, in my mind, in that the spinning wheel doesn't
> > get to dig a hole before the differential locks up.
> >
> > With automatic transmissions the subject should be as
> > simple, but the literature describes things in such a
> > was as to make things almost incomprehensible.
> >
> > The only difference between a manual and an automatic
> > should be that the clutch is replaced by a torque
> > converter and the gears and shifted automatically.
> > An automatic AWD Corolla is like this and the power
> > out of the automatic transmission goes to three
> > differentials like the manual. The only difference
> > is the locking of the center differential is automatic
> > if speed differences are detected.
> >
> > Things are not the same with Subaru automatics. First,
> > there are two kinds : the MPT and VTD. The VTD is on
> > the higher end models like the WRX and Outback H6.
> >
> > The VTD is true AWD in that it has a center differential.
> > But : the MPT, used in most models, does not have a center
> > differential. As far as I can tell power always goes to
> > the front unless the system detects a difference between
> > wheel speeds (using sensors) at which point it will engage
> > a multi-plate clutch (like in a motorcycle) to send power
> > to the rear. What Subaru doesn't say is that this will
> > only happen in the case that one of the front wheels is
> > spinning.
> >
> > I've seen lots of complaints about the Honda automatic
> > CR-V being like this, but I haven't seen anywhere that
> > the non VTD Subarus are also like this.
> >
> > In my mind, then, these automatics are front wheel drive
> > vehicles unless some very particular circumstances are
> > met.
> >
> > AWD, in my mind, is much more than something to help
> > getting unstuck. It's a matter of balance, both in
> > power application and engine braking, with everything
> > distributed to all four wheels, each doing 25% of the
> > work. There is less chance of a wheel spinning during
> > acceleration, or of a wheel locking up if you engine
> > break in slippery conditions.
> >
> > If you read texts by Subaru and Honda on their automatics
> > you get the idea that the system is constantly adjusting
> > things front to back depending on conditions. Well, it
> > may be monitoring things constantly, but it isn't doing
> > anything most of the time.
> >
> > So if you're looking at AWD for safety and fun, either
> > go with a manual, or make sure you get an automatic with
> > a center differential.
> >
> >
> >
>
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