AWD System

[svx_commuter]

Eddy,

I was looking around and I didn't see an answer to this. Please excuse me if it has come up before. The way I see it the SVX is always in front wheel drive and sometimes in rear wheel drive. Is this correct? I mean there is no way to disconnect the FWD with a solenoid or something else, is there?

Thanks

[eddycat2000]

Originally posted by svx_commuter
Eddy,

I was looking around and I didn't see an answer to this. Please excuse me if it has come up before. The way I see it the SVX is always in front wheel drive and sometimes in rear wheel drive. Is this correct? I mean there is no way to disconnect the FWD with a solenoid or something else, is there?

Thanks

The car is normally 90% FWD, when the TCU sees a differential in the readings between the two speed sensors, it engages the transfer clutches so that the split is variable to 50-50. No, barring a failure in the front diff you can't disconnect the FWD.

[svx_commuter]

Thanks Eddy. Now I have another question. You the commercials that says "transfer power from the wheels that slip to the wheels that grip"? Well, when the front wheels slip, the rear wheel drive kicks-in BUT the front wheels are not released from the power train for the automatic tranny. Is this different in the manual transmissions?

[eddycat2000]

Originally posted by svx_commuter
Thanks Eddy. Now I have another question. You the commercials that says "transfer power from the wheels that slip to the wheels that grip"? Well, when the front wheels slip, the rear wheel drive kicks-in BUT the front wheels are not released from the power train for the automatic tranny. Is this different in the manual transmissions?

I'm very aware of that ad campaign, so is Subaru, that's why you don't see it anymore...they got nipped in the butt on that particular phrase is what I was told. You see, most of the AWD cars that Subaru produced did *not* have limited slip rear ends, so in certain circumstances you could get stuck. At the last school I attended for new model update (2000 MY), the instructor told us that most new vehicles that Subaru produced from then on would have LSD's.

The AWD in a manual tranny has a sealed 3rd differential inside of the transmission. It is filled with it's own special fluid and has clutches in it like a LSD. So like a Limited Slip rear end, the more spin this 3rd diff sees, the more power gets transferred to the rear diff.

Basically it works the same as an automatic, just without the electronics applying transfer pressure.

[Mr. Pockets]

Originally posted by eddycat2000


I'm very aware of that ad campaign, so is Subaru, that's why you don't see it anymore...they got nipped in the butt on that particular phrase is what I was told. You see, most of the AWD cars that Subaru produced did *not* have limited slip rear ends, so in certain circumstances you could get stuck. At the last school I attended for new model update (2000 MY), the instructor told us that most new vehicles that Subaru produced from then on would have LSD's.

The AWD in a manual tranny has a sealed 3rd differential inside of the transmission. It is filled with it's own special fluid and has clutches in it like a LSD. So like a Limited Slip rear end, the more spin this 3rd diff sees, the more power gets transferred to the rear diff.

Basically it works the same as an automatic, just without the electronics applying transfer pressure.

This brings up an AWD question I have.

In my experience, the electronic system in my SVX reacts faster than the viscous-coupling AWD systems I've tried in manual-transmission Subarus. Is this just me, or does the SVX's AWD really react faster because it's not relying on the physical properties of the fluid in the viscous coupling?

Another question: Besides the SVX, my other AWD Subaru is a '90 Legacy. I *thought* the SVX detected wheelspin with the ABS sensors, telling the transmission to transfer torque. My wife's Legacy does not have ABS, so are there sensors in the transmission that detect the wheelspin? Is this how the SVX also works?

Haha, another: My SVX seems to react to wheelspin almost immediately where the Legacy's front wheels will slip some (as if driving a front-drive car) before the rears get their share of torque. Is the SVX system just better (I thought they were very similar) or is the Legacy just wearing out, causing it to seem slower to react?

[cocacola08]

Originally posted by eddycat2000


I'm very aware of that ad campaign, so is Subaru, that's why you don't see it anymore...they got nipped in the butt on that particular phrase is what I was told. You see, most of the AWD cars that Subaru produced did *not* have limited slip rear ends, so in certain circumstances you could get stuck. At the last school I attended for new model update (2000 MY), the instructor told us that most new vehicles that Subaru produced from then on would have LSD's.

The AWD in a manual tranny has a sealed 3rd differential inside of the transmission. It is filled with it's own special fluid and has clutches in it like a LSD. So like a Limited Slip rear end, the more spin this 3rd diff sees, the more power gets transferred to the rear diff.

Basically it works the same as an automatic, just without the electronics applying transfer pressure.

A testament to why we love having Eddy here

[LarryIII]

Eddy,


<<<The AWD in a manual tranny has a sealed 3rd differential inside of the transmission. It is filled with it's own special fluid and has clutches in it like a LSD. So like a Limited Slip rear end, the more spin this 3rd diff sees, the more power gets transferred to the rear diff. >>>

I first ran accross this technology in the late 60's. It was used by FMC Corp. to transmit high starting torque to machinery from large electric motors. It was known as a "soft start coupling. The fluid is some kind of silicone based fluid that has some interesting properties. As the shear rate increases, the viscosity increases (it gets thicker). It essentially pours like milk at rest but turns into something like silly putty or road tar at high shear. I think it was developed by either Monsanto or 3M.

Larry III

[Mr. Pockets]

Originally posted by LarryIII
Eddy,


<<<The AWD in a manual tranny has a sealed 3rd differential inside of the transmission. It is filled with it's own special fluid and has clutches in it like a LSD. So like a Limited Slip rear end, the more spin this 3rd diff sees, the more power gets transferred to the rear diff. >>>

I first ran accross this technology in the late 60's. It was used by FMC Corp. to transmit high starting torque to machinery from large electric motors. It was known as a "soft start coupling. The fluid is some kind of silicone based fluid that has some interesting properties. As the shear rate increases, the viscosity increases (it gets thicker). It essentially pours like milk at rest but turns into something like silly putty or road tar at high shear. I think it was developed by either Monsanto or 3M.

Larry III

And now it's called a 'viscous coupling,' right? I think a lot of AWD setups out there use it now - including smaller SUVs like the CR-V.

Thanks for the history!

[rufus]

Hey Larry-

I manufacture something similar to that in my "Bachelor Fridge". When I first bring it home from the store it pours (and tastes) like milk. However, after several weeks of "processing" the viscosity increases to the point where it must be disposed of in the toilet instead of the sink.

Any automotive applications you can think of for this technology?

[eddycat2000]

Originally posted by Mr. Pockets


This brings up an AWD question I have.

Okay Mr. Cubed Pockets...I'm not going to quote your whole message, (are you at work getting paid while typing these?)

1. There may be some lag in the manuals that the 4eat's don't have. I've never really noticed it...but then again I never really thought about it either.

2. The ABS sensors have absolutely no function in the AWD system. The AWD is determined by the difference the TCU sees between speed sensors 1 & 2. In earlier model 4eat equipped vehicles the speed sensors were in the speedo head, and in the transfer (extension) housing. When Subaru discontinued the use of speedo cables, the one speed sensor that fed data to the ECU and the speedo head was also used for the TCU. (So that means both sensors are mounted on the tranny).

3. The systems are identical. You may have more wear on the transfer clutches in your Legacy causing a slight lag in engagement. To my knowledge the only difference between the 2 cars transmissions is more clutches in the SVX to help beef it up a bit.

And thennnnnn....try and get some work done today Mr. Cubed Posckets!

[Mr. Pockets]

Originally posted by eddycat2000
And thennnnnn....try and get some work done today Mr. Cubed Posckets!

Says you - I've been working 8:30AM to 10:00PM every day this week on this damned level! :P

Thanks for the answers!