The Great AWD Torque Split Debate: 90/10 vs 60/40

[Chiketkd]

If you do a search, you'll find that this topic has been discussed numerous times before but no conclusive answer was ever arrived at for the USDM SVX with the transfer clutch awd system.

When the SVX was first introduced, several magazines and technical articles talked about a 60/40 torque split during normal driving (with no slippage) - but other USDM Subaru models (Impreza, Legacy) which use a similar awd system have a 90/10 torque split, which has led several people to draw the conclusion that the SVX was no different.

Over the past few months I've been researching this topic and even did some 'field research' in the passenger seat of Tom's '92 LS-L using his Subaru Select Monitor.

My Findings:
The excerpt "Multiplate Transfer Clutch" taken from the 98 page Road & Track Guide courtesy of Earthworm's site www.svx-iw.com backs up my findings in the field:

http://www.svx-iw.com/svxiw/road_track/images/45.jpg

In the awd multi-plate transfer clutch system, Solenoid C acts as an on/off switch used to fine-tune the torque split front-to-rear. However, torque split to the rear wheels never drops to 0% but closer to 5-10% (this was proven when I had my car up on SVXfiles lift with the fwd fuse engaged, but still had spinning rear wheels).

The above article describes Solenoid C as a "chatter valve" which cycles rapidly between on/off - works at a speed which most hardware store voltmeters will not be able to register. Think of the "chattering" of Solenoid C being like an elevator moving between two floors - if you want to keep the elevator suspended at the mid-point between the floors, using only an on/off switch ('on' the elevator goes up, 'off' it starts falling), someone would be able to accomplish this task by pressing the 'on' the button until the elevator reaches the desired position, followed by a rapid cycling between 'on' & 'off' to keep the elevator suspended at that point. ;)

This 'chattering' of Solenoid C is controlled by the SVX specific TCU. The Subaru Select Monitor is able to register the on/off signals being sent by the TCU to Solenoid C and calculate the effective torque split front-to-rear.

While in the passenger seat of Svxfiles's car, I had him do a few things before we pulled off. He first moved the shifter into the 'D' position - the Subaru Selector Monitor (SSM from here on) registered a split of 60/40. He then put it into the '3' & '2' positions with no change. When put into the '1' position the torque split now registered on the SSM as 50/50. In 'R' the torque split changed back to 60/40.

Svxfiles' then drove off in 'D' while I monitored the SSM. Driving around on level flat road the torque spilt varied between 70/30 to 60/40 depending on whether he was accelerating, at a steady velocity or slowing down for a stop light. At wide open throttle (i.e. power mode), the split went immediately to 50/50 and I even once, for a brief moment, saw it register as 49/51 (which theoretically is possible in the chattering on/off system).

When driving around corners, on entry the torque spilt would initially favor the front wheels at 75/25 but then shift back to 60/40 on exit.

Conclusion: While the SSM isn't infallible, it is the official licensed device authorized by Subaru to correctly monitor/diagnose their cars. So who's right 90/10 or 60/40??? Both. Why, because SVX the transfer clutch awd system works between the extremities of 50/50 to ~90/10 when dividing torque. However, those are the extremities and the torque split never stays at either one unless forced to (i.e. power mode or fwd fuse). But, when cruising along a dry, flat interstate with the torque converter locked up at 65mph, torque split is 60/40 in the SVX. :)

[Weasel 22]

very informative..I too often wonder as to what the split currently is on my SVX while driving in varying conditions

[Beav]

I didn't realize anyone thought it was a 'one or the other' type arrangement. It definitely is a continuously variable affair.

Monitors are notoriously slow in reporting what is happening. I suppose the ECU/TCU is more concerned with maintaining vehicle operation than reporting it. Real time action can be viewed with a meter that has a duty cycle settting.

I must be missing something, how is it possible for the system to go 49/51? I realize the monitor may very well display that, they aren't totally 100% accurate (believe it or not.) It's just that at 100% application the torque can only be split evenly, right? (applied equally, front & rear)

[michael]

OK so does this mean there is no difference between the usdm and jdm transmissions?

[Chiketkd]

I didn't realize anyone thought it was a 'one or the other' type arrangement. It definitely is a continuously variable affair.

Monitors are notoriously slow in reporting what is happening. I suppose the ECU/TCU is more concerned with maintaining vehicle operation than reporting it. Real time action can be viewed with a meter that has a duty cycle settting.

I must be missing something, how is it possible for the system to go 49/51? I realize the monitor may very well display that, they aren't totally 100% accurate (believe it or not.) It's just that at 100% application the torque can only be split evenly, right? (applied equally, front & rear)
Only the most sensitive meters with a duty cycle setting can monitor the rapid on/off of solenoid C. A cheap $10-$20 voltmeter will not be able to accomplish this... ;)

The SSM would have some small % of error, but from my understanding of the 4EAT, 100% of torque is sent to the back of the transmission, where the split front-to-rear occurs. With a 'chatter valve' that works in an on/off fashion, theoretically it is possible to go past the desired position briefly when switching between on & off.

http://www.svx-iw.com/svxiw/road_track/images/44.jpg

If the torque split can never be more than 50% rear, then it is possible that the SSM has an error of 1%. Either way, while a sensitive duty cycle voltmeter can register the on/off activity of Solenoid C, it would be next to impossible to figure out the effective torque split. The factory made and licensed Subaru Select Monitor was designed to do just this... :cool:

-Chike

[Chiketkd]

OK so does this mean there is no difference between the usdm and jdm transmissions?
There's a huge difference. The JDM and 99+ USDM 4EAT's use a VTD system that electronically varies torque front to rear (no transfer clutch & Solenoid C). On the JDM models, the torque split starts out at 33.33% front/ 66.66% rear - on USDM models it's 50%/50%. :)

-Chike

[n00b on demand]

60/40 huh? Is that why i could take a sharp corner going 70? ....not that i have ;)

[GreenMarine]

That is AWESOME information!!! I can't believe that everything that I have been reading and repeating to others over the past few years has been wrong (the 90/10 thing).... I can't wait till ECUTune comes out with their Engine monitoring system!!! I want one soo bad!!! Not that it matters all that much anymore since I don't have an Auto Tranny anymore :rolleyes::)

[IggDawg]

no kidding... this is VERY cool info. and I assume all this is due to the TCU, so the fact that I have (what I assume to be) a legacy transmission, it should still behave the same way? Any idea if this is standard behavior for all MPT 4EATs?

[Mr. Pockets]

I didn't realize anyone thought it was a 'one or the other' type arrangement. It definitely is a continuously variable affair.

I wasn't aware that people were confused on the issue, either. I'm glad Chike posted the information for those who, unlike me, haven't had to learn a lot about the tranny because they put it back together wrong. :p

[svxfiles]

One of the SVXi we ran the tests in was my car which has a Legacy outback transmission (W/4.44 gears :) ) and another time Diana was driving her stock 92 SVX and I was on the phone to Chi ke, while Di and I ran the same tests.
Since the TCU controls the trans, they both acted the same way. Tom.

[SVXRide]

One of the SVXi we ran the tests in was my car which has a Legacy outback transmission (W/4.44 gears :) ) and another time Diana was driving her stock 92 SVX and I was on the phone to Chi ke, while Di and I ran the same tests.
Since the TCU controls the trans, they both acted the same way. Tom.

Tom,
Remember that we did the same thing with the SSM in my car at the "drag meet" at Mason-Dixon. Of course the TCU was sending the 40% into a "black hole" as the Solenoid C was not functioning at the time...
-Bill (enjoying the start of a new season of autoX - especially with a functioning AWD system!!)

[87f383]

awesome info... I don't drive a gloried FWD car anymore... lol

[red95svx]

I remember the 90/10 60/40 debates from my Yahoo days. I believed it was 60/40 by default, others disagreed. Eddycat, wherever you are, the joke is finally on you.:) 60/40!!




Dave

[Beav]

Good grief. Look at it this way: the power goes to the rear of the trans. At the rear of the tranny is a drive gear and a driven gear. The driven gear sends power back to the front, to the front diff. This is how a fwd trans would work. AWD is accomplished by adding a clutch to the rear of the the drive gear. The rear of the clutch is attached to the rear driveshaft. The clutch engages and sends power to the rear wheels. When the clutch is disengaged 100% of the power would go forward. When the clutch is 100% engaged the power is shared by the front and rear, or another way of saying it is .... tada!! 50-50. Physically impossible to be any more than that with the drive/driven gears @ 1:1.

I can't imagine why this would be an issue to haggle over, it is really quite simple.

Regarding the 51%, don't go overboard - it's just a scanner snafu and believe me, every scanner built has plenty of those. Why do you think techs double check the scanner findings with a meter?

[oab_au]

Well I wrote this in a thread called.' Can I "turn off" the AWD ' back about Jan this year.

"Yes well when they quote the torque split for the VTD, they seem to put it as 40% 60%, instead of the actual 36/64 that it is. Now I suspect that this was, then applied to the Transfer system, the other way around.

The Transfer system torque split varies with a number of inputs. Selected gear, road speed, and throttle opening. The split is highest with the lowest gear, the lowest speed and the highest throttle opening.

To put this into numbers, when it is in 4th at 30mph/60kph, and you are accelerating hard, the split would be around 60/40, as the road speed rises, the split will reduce to say 75/25. As soon as you lift the foot, the split will reduce to 90/10.
When you are taking off hard in 1st, the split is 50/50, as there is a high chance of wheel spin, so the torque split is increased to max. As the speed rises, the split reduces.

So mate it is hard to state what the standard split would be, just driving down the road. If you are just cruising, it would be 90/10, hit the throttle to overtake, it would go to say 70/30, lift the foot, back to 90/10. It will allways vary to suit the conditions, though it allways needs some drive to the rear, to prevent the rear drive line from shunting. ".

Pretty close to what you have seen. I agree with Beav, 49/51 is not possible.

Harvey. :)

[Chiketkd]

Well I wrote this in a thread called.' Can I "turn off" the AWD ' back about Jan this year.

"Yes well when they quote the torque split for the VTD, they seem to put it as 40% 60%, instead of the actual 36/64 that it is. Now I suspect that this was, then applied to the Transfer system, the other way around.

The Transfer system torque split varies with a number of inputs. Selected gear, road speed, and throttle opening. The split is highest with the lowest gear, the lowest speed and the highest throttle opening.

To put this into numbers, when it is in 4th at 30mph/60kph, and you are accelerating hard, the split would be around 60/40, as the road speed rises, the split will reduce to say 75/25. As soon as you lift the foot, the split will reduce to 90/10.
When you are taking off hard in 1st, the split is 50/50, as there is a high chance of wheel spin, so the torque split is increased to max. As the speed rises, the split reduces.

So mate it is hard to state what the standard split would be, just driving down the road. If you are just cruising, it would be 90/10, hit the throttle to overtake, it would go to say 70/30, lift the foot, back to 90/10. It will allways vary to suit the conditions, though it allways needs some drive to the rear, to prevent the rear drive line from shunting. ".

Pretty close to what you have seen. I agree with Beav, 49/51 is not possible.

Harvey. :)
Harv,

I must agree that more than 50% to the rear wheels would be an impossibility based on the design of the awd 4EAT.

In the above info, in MY 'field testing' I never once saw a torque split of 90/10 when cruising along a flat highway at a constant speed. With the shifter in 'D' the torque split always defaulted to 60/40. The harder you accelerated, the split would shift to 50/50; the faster you took a corner, the more the torque would go towards the front wheels on entry at 75/25.

-Chike

[Chiketkd]

awesome info... I don't drive a gloried FWD car anymore... lol
I know what you mean... ;)

The SSM is an amazing device that Subaru developed. :)

-Chike

[Chiketkd]

no kidding... this is VERY cool info. and I assume all this is due to the TCU, so the fact that I have (what I assume to be) a legacy transmission, it should still behave the same way? Any idea if this is standard behavior for all MPT 4EATs?
Correct. The TCU part # for the SVX 4EAT, is different than the one used in the Impreza & Legacy cars of similar model years.

I even bought an awd '93 Legacy TCU just to experiment and noticed a sharp difference in the way it controlled my car. Front wheel spin was definitely easier to come by...

Subaru basically developed a specific TCU for the SVX with a greater emphasis towards performance driving...

-Chike

[thundering02]

Since it seams like were only talking voltage to a solonoid would it be thereticly possible to change it manually....namely wiring a potetiometer and just "dailing" the tourqe that you want

[Chiketkd]

Since it seams like were only talking voltage to a solonoid would it be thereticly possible to change it manually....namely wiring a potetiometer and just "dailing" the tourqe that you want
This has been done before by people trying to keep the trans in 50/50 mode. However doing this will cause the drivetrain to bind in turns (unless driving on loose gravel or snow). It's only useful when going in a straight line (e.g. drag racing).

I think it was Guard-TL who wired up switches to put his trans in three different modes: regular awd, fwd (more like 90/10 or 95/5) and 4wd (50/50).

-Chike

[Chiketkd]

Tom,
Remember that we did the same thing with the SSM in my car at the "drag meet" at Mason-Dixon. Of course the TCU was sending the 40% into a "black hole" as the Solenoid C was not functioning at the time...
-Bill (enjoying the start of a new season of autoX - especially with a functioning AWD system!!)
This is a good point you mentioned here Bill. The TCU is sending signals to the Solenoid C to vary torque regardless of whether the solenoid is functioning or not. If the solenoid is inactive, then 100% of your power will go to the rear wheels as the transfer clutch can no longer function.

A properly functioning Solenoid C will basically 'chatter' on & off incessantly to follow the TCU's commands.

-Chike

[SVXRide]

This is a good point you mentioned here Bill. The TCU is sending signals to the Solenoid C to vary torque regardless of whether the solenoid is functioning or not. If the solenoid is inactive, then 100% of your power will go to the front wheels as the transfer clutch can no longer function.

A properly functioning Solenoid C will basically 'chatter' on & off incessantly to follow the TCU's commands.

-Chike

Chike,
fixed your post... :D
-Bill

[TomsSVX]

all this info on the auto got me thinking. What is the split for a 91 4.11 legacy mt? Just curious. If anyone knows, let me know.

Tom

[Chiketkd]

Chike,
fixed your post... :D
-Bill
Thanks! I wish that was the case... ;)

-Chike

[Chiketkd]

all this info on the auto got me thinking. What is the split for a 91 4.11 legacy mt? Just curious. If anyone knows, let me know.

Tom
Someone correct me if I'm wrong, but I've read that the awd Subaru 5MT's use a viscous coupling center diff to vary torque from an pre-set 50/50 split...

-Chike

[red95svx]

Someone correct me if I'm wrong, but I've read that the awd Subaru 5MT's use a viscous coupling center diff to vary torque from an pre-set 50/50 split...

-Chike


That is what I heard.




Dave

[TomsSVX]

so the mt's are usually 50/50 like the autos are 60/40? just making sure i understand.

Tom

[IggDawg]

non-wrx MTs are 50/50 and any slippage will make that split vary, but the VC diff "tries" to get that 50/50 split back when the VC fluid is stressed and heated. it reacts to any difference in spin between the front and back wheels.

the WRXs are 55/45 IIRC, but react the same way.

aside - the AWD system in an auto is arguably "better" since it reacts to the changes in conditions so much faster (electronic sensors vs. heating up a fluid). When a friend of mine took his auto WRX to the Tim O'Neil winter driving school, Tim commented on how much better the auto AWD system felt than the manual.

[TomsSVX]

ah, gotcha thnx for the valuable info.

Tom

[Earthworm]

The WRX 5MT in mine has to be 50/50. The AWD doesn't behave anywhere near the same as the 4EAT it replaced. It behaves exactly like my Justy when I lock it into 4WD. (Except for the binding in the corners)

[Chiketkd]

aside - the AWD system in an auto is arguably "better" since it reacts to the changes in conditions so much faster (electronic sensors vs. heating up a fluid). When a friend of mine took his auto WRX to the Tim O'Neil winter driving school, Tim commented on how much better the auto AWD system felt than the manual.
That's what I've heard as well. The electronic awd system in the auto trans shifts torque much quicker and before any traction loss occurs. Changes in torque split can happen as a result of steering input, braking, gradient of road, etc.

In the 5MT viscous coupling awd, a change in torque split only occurs when there's a loss of traction.

This is one reason why it's next to impossible to get an awd 4EAT stuck in snow, sand, mud, etc., but it's much easier with a 5MT... ;)

Remember this pic:

http://www.fayettevilleracing.com/pictures/various/wrx%20in%20sand.jpg

-Chike

[Ron Mummert]

It's good to see Chike, Beav, Harvey & others giving 110% to this topic.

Ron. (counting toes).

[LarryIII]

Chicke,

Thanks for conducting this experiment and posting this information.

[MPtyza]

Correct. The TCU part # for the SVX 4EAT, is different than the one used in the Impreza & Legacy cars of similar model years.

I even bought an awd '93 Legacy TCU just to experiment and noticed a sharp difference in the way it controlled my car. Front wheel spin was definitely easier to come by...

Subaru basically developed a specific TCU for the SVX with a greater emphasis towards performance driving...

-Chike

Hmm, that gets me thinking. I've got a '91 Legacy Turbo. Since you swapped a Legacy TCU into an SVX, would the opposite be possible? Like could I get the 60/40 split in my Legacy if I swapped in the AWD SVX TCU do you think?

Sorry to hijack your thead a little, but that question is burning a hole in my head right now

[Chiketkd]

Chicke,

Thanks for conducting this experiment and posting this information.
You're welcome Larry. I just didn't get the 'feeling' out cars had a 90/10 torque split as the front tires didn't spin during hard launches (either all four spun, or none at all).

Hopefully, this'll put one myth to rest. The Subaru Select Monitor did provide very compelling evidence - which was backed up on different occassions in different cars by Green_eyed_lady, SVXRide and SVXfiles.

-Chike

[Chiketkd]

Hmm, that gets me thinking. I've got a '91 Legacy Turbo. Since you swapped a Legacy TCU into an SVX, would the opposite be possible? Like could I get the 60/40 split in my Legacy if I swapped in the AWD SVX TCU do you think?

Sorry to hijack your thead a little, but that question is burning a hole in my head right now
It may work, but then again it may not. The older Legacys didn't use an electronic speed sensor and the TCU didn't send the ECU a signal to reduce torque on the 1-2 and 2-3 shifts.

-Chike

[IggDawg]

more interesting info... I didn;t know there was no torque cut signal on 3-4... maybe this is why the 3-4 shift seems laggier than the others.

I need another shift kit =D. I miss the hard shifts.

[svxistentialist]

You're welcome Larry. I just didn't get the 'feeling' out cars had a 90/10 torque split as the front tires didn't spin during hard launches (either all four spun, or none at all).

Hopefully, this'll put one myth to rest. The Subaru Select Monitor did provide very compelling evidence - which was backed up on different occassions in different cars by Green_eyed_lady, SVXRide and SVXfiles.

-Chike

Thanks Chike.

Good solid measured information.

It would be interesting to get the same information on my JDM and UK SVX trannies, and also on my Legacy twin turbo with 4EAT.

Where did you get the SSM, might I ask? Can one be bought for reasonable money? My brother has a JDM Forester Turbo, which is pretty quick. All our cars OBD I. We are discussing getting a select monitor.

Can you help?

Joe :D

[And I promise to post up the Euro and JDM torque split figures when I get it :D ]

[n00b on demand]

So if the split is really 60/40 then why have people all this time thought it was 90/10? AWD is so awesome :D

[oab_au]

I don't know about dispelling a myth, as creating a monster :)

It does not matter what number is given to it, the fact remains that the torque split is constantly varying to suit the conditions. The select monitor, really shows the % duty cycle, that is sent to the C solenoid, and this varies from 5%, clutch off to 95% clutch on. You can hear this, by turning the ignition on, don't start the motor, select D,and just move the accelerator from closed to open, you can hear the solenoid buzzing louder as the pedal is pushed down.

The pressure is increased, the more the throttle is opened, and the lower the gear. This is to prevent the front wheels from spinning, due to the higher torque that is applied in these conditions. Once the torque is reduced in the higher gears, and the throttle opening is reduced as the speed rises, the clutch pressure is reduced. It doesn't just stay at the same torque split, all the time.

The only 4eat that has a fixed torque split, is the VTD, at 36% front 64% rear. This split is due to the differential leverage of the gears in the compound planetary diff. This trans runs this torque split all the time, only applying the Limited slip clutch, under the same conditions of starting and hard acceleration, or wheel spin.

The main difference is in hard acceleration and cornering. As Chike has noted in the Transfer system, the torque split is reduced, when turning into corners, and increased when exiting the corner. This is because the split has to be reduced to allow for the difference in front/rear wheel speed, then increased when this difference is reduced, as the same clutch can't apply full torque to the rear wheels, and allow slip for cornering at the same time.

I have found this in driving my Liberty with the Transfer system. Stick the foot down coming into a corner, and it dies a bit till its half way through, then away it goes. The VTD SVX does not do this, just line up the corner, plant the foot, and it just accelerates through the corner, no lag, no under steer :cool:

Some other points that I see. All 4eats send a torque reduction signal on all changes. They all use electronic sensing to check for wheel spin. Road grade doesn't affect the split. The TCU for the different 4eats are tailored to suit the car, so they will be different, but interchangeable.


Harvey. ;)

[TomsSVX]

geeze you are a wealth of knowledge on subarus. Will you come live in my garage? i have some moving blankets and a toilet across the hall. I will feed u once and a while. Mostly you will just tell me everything about my car all the time so there is no guessing.

Tom

[Chiketkd]

Thanks Chike.

Good solid measured information.

It would be interesting to get the same information on my JDM and UK SVX trannies, and also on my Legacy twin turbo with 4EAT.

Where did you get the SSM, might I ask? Can one be bought for reasonable money? My brother has a JDM Forester Turbo, which is pretty quick. All our cars OBD I. We are discussing getting a select monitor.

Can you help?

Joe :D

[And I promise to post up the Euro and JDM torque split figures when I get it :D ]
No prob Joe. I don't own a Subaru Select Monitor - Svxfiles does. He used to be a salesman at a Subaru dealership for many years. Not sure how one can be acquired either. These monitors weren't available to the general public, only authorized Subaru dealerships could purchase them (to the best of my knowledge).

-Chike

[TomsSVX]

This is one reason why it's next to impossible to get an awd 4EAT stuck in snow, sand, mud, etc., but it's much easier with a 5MT... ;)

Remember this pic:

http://www.fayettevilleracing.com/pictures/various/wrx%20in%20sand.jpg

-Chike

No, This is why you dont take a subaru on the beach. In sand there are two things u need, air downed tires and clearance, which is hard to do with any car unless you are Jesse. That imprezza is sunk to the frame because they lacked clearance not traction from all fours. Not trying to shoot you down at all just saying, I live on the beach and have seen many auto and mt subaru shoobies get stuck. I usually just point and laugh then drive away in my suby.

Tom

[Chiketkd]

I don't know about dispelling a myth, as creating a monster :)

It does not matter what number is given to it, the fact remains that the torque split is constantly varying to suit the conditions. The select monitor, really shows the % duty cycle, that is sent to the C solenoid, and this varies from 5%, clutch off to 95% clutch on. You can hear this, by turning the ignition on, don't start the motor, select D,and just move the accelerator from closed to open, you can hear the solenoid buzzing louder as the pedal is pushed down.

The pressure is increased, the more the throttle is opened, and the lower the gear. This is to prevent the front wheels from spinning, due to the higher torque that is applied in these conditions. Once the torque is reduced in the higher gears, and the throttle opening is reduced as the speed rises, the clutch pressure is reduced. It doesn't just stay at the same torque split, all the time.

The only 4eat that has a fixed torque split, is the VTD, at 36% front 64% rear. This split is due to the differential leverage of the gears in the compound planetary diff. This trans runs this torque split all the time, only applying the Limited slip clutch, under the same conditions of starting and hard acceleration, or wheel spin.

The main difference is in hard acceleration and cornering. As Chike has noted in the Transfer system, the torque split is reduced, when turning into corners, and increased when exiting the corner. This is because the split has to be reduced to allow for the difference in front/rear wheel speed, then increased when this difference is reduced, as the same clutch can't apply full torque to the rear wheels, and allow slip for cornering at the same time.

I have found this in driving my Liberty with the Transfer system. Stick the foot down coming into a corner, and it dies a bit till its half way through, then away it goes. The VTD SVX does not do this, just line up the corner, plant the foot, and it just accelerates through the corner, no lag, no under steer :cool:

Some other points that I see. All 4eats send a torque reduction signal on all changes. They all use electronic sensing to check for wheel spin. Road grade doesn't affect the split. The TCU for the different 4eats are tailored to suit the car, so they will be different, but interchangeable.


Harvey. ;)
Not creating any monsters here Harv, as my results were backed up by the Subaru Select Monitor and three other members who got the same results.

Never once during my 'field test' did I see a torque split of 90/10. The torque seemed to level out to 60/40 when going in straight line on a flat road after the torque converter locked up. This was also the torque value that displayed on the monitor before we pulled off and put the slector in 'D', '3' and '2'.

I agree that the torque split changes constantly, but it's only when there's a change in the steering, braking, acceleration, etc. I noticed a chnage in split when we went up a steeper gradient, but the road may not have been straight, and this could have been due to changes in steering input.

When I plugged te '93 awd Legacy TCU into my car, the 1-2 and 2-3 shifts definitely DID NOT have any torque reduction.

I did my homework, these were my results. ;)

-Chike

[mbtoloczko]

That's what I've heard as well. The electronic awd system in the auto trans shifts torque much quicker and before any traction loss occurs. Changes in torque split can happen as a result of steering input, braking, gradient of road, etc.

In the 5MT viscous coupling awd, a change in torque split only occurs when there's a loss of traction.

This is one reason why it's next to impossible to get an awd 4EAT stuck in snow, sand, mud, etc., but it's much easier with a 5MT... ;)

...

-Chike

Hi Chike, I think there's a little more to it than just the viscous coupling on the 5MT vs the active center diff on 4eat. The standard viscous center diff on the 5MT is very weak. For all intents, its an open diff. With a stronger viscous coupling on the center diff, I'd guess that at least as straight line traction goes, the 5MT could do much better.

[UberRoo]

One thing I would suggest be kept in mind is that the TCU does not have any sensors that are able to measure torque split. The readings given by the select monitor are only duty-cycle readings. A 10%, 50%, or 90% duty cycle does not necessarily mean you are getting 10%, 50%, or 90% torque transfer to the rear wheels. This is especially true if the transmission isn't in top condition, but even under the best possible circumstances, input values are not a good indicator of response. For example, half-opened valve does not mean only half the flow, or half pressure. In this example, if the plumbing is sufficiently large, a valve might need to be 90% closed to restrict any fluid at all. (Another example is the throttle valve in your car: the gas pedal. Ever notice how there isn't much difference between pushing the pedal halfway down and all the way down? There's a big difference between idle and 1/4 throttle, but not as much between 1/4 and 1/2, and almost no difference between 1/2 and wide open.)

I strongly suspect that the 90/10 and 50/50 figures are very much closer to the truth. I'd wager that even the slightest activity of the duty solenoid would necessarily cause at least a 90/10 torque split. It would be very difficult to modulate less than that. Even disabling the solenoid completely might not reduce torque split less than that. I'd also wager that the torque split does not increase significantly until the duty cycle reaches the upper 90% range. In these upper ranges, the degree of control would be marginal and it would be difficult to regulate torque split. In this upper range, torque split would probably be mostly 49% and 50%.

Although the TCU makes great efforts to precisely control the torque split, I think the reality is that it's mostly just on or off. Quite frankly, there's no large fault with that. It works very well that way.

[Chiketkd]

Hi Chike, I think there's a little more to it than just the viscous coupling on the 5MT vs the active center diff on 4eat. The standard viscous center diff on the 5MT is very weak. For all intents, its an open diff. With a stronger viscous coupling on the center diff, I'd guess that at least as straight line traction goes, the 5MT could do much better.
Good point Mychailo. I guess changing to an adjustable STI center diff would reap benefits... :)

-Chike

[Chiketkd]

One thing I would suggest be kept in mind is that the TCU does not have any sensors that are able to measure torque split. The readings given by the select monitor are only duty-cycle readings. A 10%, 50%, or 90% duty cycle does not necessarily mean you are getting 10%, 50%, or 90% torque transfer to the rear wheels. This is especially true if the transmission isn't in top condition, but even under the best possible circumstances, input values are not a good indicator of response. For example, half-opened valve does not mean only half the flow, or half pressure. In this example, if the plumbing is sufficiently large, a valve might need to be 90% closed to restrict any fluid at all. (Another example is the throttle valve in your car: the gas pedal. Ever notice how there isn't much difference between pushing the pedal halfway down and all the way down? There's a big difference between idle and 1/4 throttle, but not as much between 1/4 and 1/2, and almost no difference between 1/2 and wide open.)

I strongly suspect that the 90/10 and 50/50 figures are very much closer to the truth. I'd wager that even the slightest activity of the duty solenoid would necessarily cause at least a 90/10 torque split. It would be very difficult to modulate less than that. Even disabling the solenoid completely might not reduce torque split less than that. I'd also wager that the torque split does not increase significantly until the duty cycle reaches the upper 90% range. In these upper ranges, the degree of control would be marginal and it would be difficult to regulate torque split. In this upper range, torque split would probably be mostly 49% and 50%.

Although the TCU makes great efforts to precisely control the torque split, I think the reality is that it's mostly just on or off. Quite frankly, there's no large fault with that. It works very well that way.
UberRoo,

What you're saying makes good sense in theory, but is hard to prove in reality.

I've posted my results using the SSM when in the awd diagnostic mode. The excerpt I posted at the start of this thread from the Road & Track Guide about the multi-plate transfer clutch seemed to reiterate these findings.

If you or Harv can think of an elegant way to show the torque split is closer to 90/10 than 60/40 in normal driving (with no braking, acceleration or steering inputs affecting transfer) then by all means prove these results wrong. ;)

-Chike

[svxistentialist]

Chike

You might have missed the question in my post back a ways;

Is it possible to buy a Subaru Select Monitor?

If so, from where and how much?

Thanks

Joe :)

[Hocrest]

Chike

You might have missed the question in my post back a ways;

Is it possible to buy a Subaru Select Monitor?

If so, from where and how much?

Thanks

Joe :)


I've seen them show up on EBAY from time to time...

I think I was told that in addition to the SSM you will also need the SVX module/adapter?????

[svx_commuter]

Chike, I think this is a great thread with very good information and I am glad to see someone take interest in "exploring" the SVX and it's working. :)

That is all I wanted to say and then I got thinking about this and driving around without a 90/10 split on the highway is really bad for mileage. Has anyone discussed the fact that the line pressure feeds the transfer solenoid? Perhaps maybe someday someone could correlate the line pressure and duty cycle from the transfer solenoid "C" with the actual pressure in the transfer housing. As I remember the EAT hydraulic line pressure varies with the throttle position. The line pressure which varies with the throttle setting then goes to the transfer solenoid "C" which regulates the hydraulic pressure going to the transfer clutch plates.

So if the line pressure resistor by the battery is pulled or if a vacuum switch kit (small car) is installed, the line pressure is maximum at all throttle settings. Then 100% line pressure is fed to the transfer solenoid all the time. In this case the duty cycle numbers you read would be regulating the maximum pressure all the time and the duty cycle numbers would be equated to the torque split front/rear.

When the line pressure is allowed to vary with the TPS setting, a lower line pressure is present with light throttle and maximum line pressure is available when the pedal is on the floor. This is totally independent of the transfer duty solenoid. A lower line pressure fed to the transfer solenoid that is wide open allows the low line pressure to enter the transfer clutch.

The higher the pressure is to the transfer clutches the closer the SVX is to 50/50 and the faster the transfer clutches or something else wears out due to the forced slipping of the clutch plates when cornering.

[oab_au]

UberRoo,

What you're saying makes good sense in theory, but is hard to prove in reality.

I've posted my results using the SSM when in the awd diagnostic mode. The excerpt I posted at the start of this thread from the Road & Track Guide about the multi-plate transfer clutch seemed to reiterate these findings.

If you or Harv can think of an elegant way to show the torque split is closer to 90/10 than 60/40 in normal driving (with no braking, acceleration or steering inputs affecting transfer) then by all means prove these results wrong. ;)

-Chike

Hi Chike,I am not trying to disprove what you say. I am only telling it like it is.

If you read back, on what I have written on the subject over the years, you will find that, I have allways been saying the same things. If you believed I said "that the split was allways fixed at 90/10", then you have not read what I have previously said.

When the Road & Track report is used as "The Gospel ",to prove a technical point, I do tend to worry about the resultant conclusion. Just in the bit that you have posted to 'reiterate your findings', we find that they say," that the signal for the Transfer, comes from the ABS brake system". :eek: They get a bit confused on the technical bits. :)

If you get to look at the Work Shop Manual, you will find a 3 Dimensional map, that shows the clutch pressure, relative to, selected gear, speed and throttle opening, that is a better guide to base conclusions on.

Harvey. ;)

[oab_au]

Chike, I think this is a great thread with very good information and I am glad to see someone take interest in "exploring" the SVX and it's working. :)

That is all I wanted to say and then I got thinking about this and driving around without a 90/10 split on the highway is really bad for mileage. Has anyone discussed the fact that the line pressure feeds the transfer solenoid? Perhaps maybe someday someone could correlate the line pressure and duty cycle from the transfer solenoid "C" with the actual pressure in the transfer housing. As I remember the EAT hydraulic line pressure varies with the throttle position. The line pressure which varies with the throttle setting then goes to the transfer solenoid "C" which regulates the hydraulic pressure going to the transfer clutch plates.

So if the line pressure resistor by the battery is pulled or if a vacuum switch kit (small car) is installed, the line pressure is maximum at all throttle settings. Then 100% line pressure is fed to the transfer solenoid all the time. In this case the duty cycle numbers you read would be regulating the maximum pressure all the time and the duty cycle numbers would be equated to the torque split front/rear.

When the line pressure is allowed to vary with the TPS setting, a lower line pressure is present with light throttle and maximum line pressure is available when the pedal is on the floor. This is totally independent of the transfer duty solenoid. A lower line pressure fed to the transfer solenoid that is wide open allows the low line pressure to enter the transfer clutch.

The higher the pressure is to the transfer clutches the closer the SVX is to 50/50 and the faster the transfer clutches or something else wears out due to the forced slipping of the clutch plates when cornering.

Gidáy John, don't think the select monitor knows the final pressure, :D yes it only knows the signal sent to the solenoid. The actual pressure on the plates, varies with the line pressure, that is set by the A solenoid.

To put it easy, the C solenoid does not vary line pressure. It varies a regulated pilot pressure, that moves a spool valve, that applies line pressure to the clutch plates. As John says the resultant torque split depends on the line pressure, that the TCU can not read.

So as John says. the only sure way to tell the clutch pressure affecting the torque split, is by monitoring the actual pressure applied to the clutch plates.
The plot thickens. :D
Harvey.

[Chiketkd]

Chike

You might have missed the question in my post back a ways;

Is it possible to buy a Subaru Select Monitor?

If so, from where and how much?

Thanks

Joe :)
Sorry Joe. I have no idea where to purchase a Subaru Select Monitor. :confused: :confused: :confused:

I think Hocrest mentioned that they're sold on Ebay ocassionally - that would be the best bet if you ask me.

-Chike

[Chiketkd]

When the Road & Track report is used as "The Gospel ",to prove a technical point, I do tend to worry about the resultant conclusion.
Harv,

I'm not using the Road & Track Guide as "Gospel" - if you look over my initial post, you'll see I center my conclusion around the results of my field research using Tom's Subaru Select Monitor. ;) As far as I know, no one has ever done testing on the torque split of the USDM SVX using a Subaru Select Monitor before...

How about looking at this problem in a different light. Do you know of anyone in OZ land who can loan you a SSM that'll be compatible with your VTD SVX? If so, I'll be interested in knowing the torque split values it'll show for your trans. If it accurately reads the preset 33.3%/66.7%, then I'm sure a similar licensed SSM is accurately reading the torque split on the 3 USDM SVXs we've tested (Svxfiles's, Green_eyed_lady & SVXRide).

BTW, I know you're not saying the torque split is 90/10 - as you keep mentioning that it's always changing (I have re-affirmed this as well in the findings I posted). However, you HAVE mentioned in previous threads that when cruising on a highway at a relatively constant speed, the torque split would be very close to this value (95/5-90/10). My point of contention, is that not once during my testing with the SSM did I ever see the torque split registering anything close to this value. Even at a standstill in 'D', it showed 60/40... :)

-Chike

[UberRoo]

UberRoo,

What you're saying makes good sense in theory, but is hard to prove in reality.

I've posted my results using the SSM when in the awd diagnostic mode. The excerpt I posted at the start of this thread from the Road & Track Guide about the multi-plate transfer clutch seemed to reiterate these findings.

If you or Harv can think of an elegant way to show the torque split is closer to 90/10 than 60/40 in normal driving (with no braking, acceleration or steering inputs affecting transfer) then by all means prove these results wrong. ;)

-Chike
You're definitely very right about one thing: It's very hard to prove. The best way to attempt to prove my theory is to hook up a pressure gauge to the transfer clutch pressure lines. I'm quite confident that if you compared the pressure readings to the duty cycle indicated on the select monitor, the readings would not closely relate. The pressure applied to the transfer clutch is a very good indicator of the amount of torque available to the rear wheels. (It is not however, a good indicator of the percent of torque applied to the rear wheels. This depends on the amount of traction available to the front wheels, the amount of slippage, and the amount of engine power supplied.)

Measuring the torque applied to the wheels requires some pretty fancy engineering. I don't think any of us are going to be proving anything any time soon. I'm pretty sure even Subaru doesn't know. They theorized, no doubt, but I'm sure trial and error was the method used to get it right. I do know for a fact that valves do not behave in a linear fashion. Even needle valves and other, more exotic, specially designed valves only behave in a linear fashion at specific available rates of flow and pressure with specific viscosity fluids. Fluid systems just aren't that well-behaved. Much like 1/4, 1/2, and 3/4 throttle doesn't make you go 25, 50, and 75 miles per hour respectively, very few valves will regulate pressure or flow in the same way.

I think that oab_au and I both appreciate that the select monitor only shows what the TCU is trying to achieve, but not what is actually happening. Regarding the information provided by Road & Track, what is their source? Did they test it? If so, how? (Personally, I detest the media because it is so chronically full of misinformation.) If you reeeally want to know what's happening, a pressure gauge will give you the best data. What it tells you is far, far more meaningful than the select monitor.

[oab_au]

Harv,

I'm not using the Road & Track Guide as "Gospel" - if you look over my initial post, you'll see I center my conclusion around the results of my field research using Tom's Subaru Select Monitor. ;) As far as I know, no one has ever done testing on the torque split of the USDM SVX using a Subaru Select Monitor before...

How about looking at this problem in a different light. Do you know of anyone in OZ land who can loan you a SSM that'll be compatible with your VTD SVX? If so, I'll be interested in knowing the torque split values it'll show for your trans. If it accurately reads the preset 33.3%/66.7%, then I'm sure a similar licensed SSM is accurately reading the torque split on the 3 USDM SVXs we've tested (Svxfiles's, Green_eyed_lady & SVXRide).

BTW, I know you're not saying the torque split is 90/10 - as you keep mentioning that it's always changing (I have re-affirmed this as well in the findings I posted). However, you HAVE mentioned in previous threads that when cruising on a highway at a relatively constant speed, the torque split would be very close to this value (95/5-90/10). My point of contention, is that not once during my testing with the SSM did I ever see the torque split registering anything close to this value. Even at a standstill in 'D', it showed 60/40... :)

-Chike

Well you don't need a Select Monitor to read the duty cycle that is sent from the TCU, any good digital multi meter can read duty cycle %, do it, I use a Fluke mod 19.
Doing the same to the VTD won't give the same results. It will only, show the % signal sent to the Limited Slip Clutch. The torque is divided by the gears in the diff, to the ratio of 36.4 F/ 63.6 R (not 33.3/66.7), the TCU does not control this split.
The LSC is set to the driving conditions, to prevent wheel spin. So like your model, it will be applied "standing still in D", because it is ready for the start, when wheel spin is most likely. Just that, in the Euro, it is the rear wheels that spin first, due to them getting the most torque.
I reckon if you cruised at about 80 MPH in D on a light throttle, you would see a lower signal. Not that it matters, as soon as you hit the pedal the signal would go up.

Harvey. ;)

[oab_au]

About what SVXCommuter said, about the line pressure to the Transfer clutch with the dropping resistor disconnected. This would explain the problems that some have with transfer clutch binding, when the resistor is disconnected, or if the Shift kit is adjusted too much.
In short, the TCU sets the line pressure by adjusting the A solenoid, it knows what the pressure should be, so it sends the apropreate signal to the clutch, but if the pressure is higher, due to the resistor, the clutch pressure will be higher, to cause the binding.

Harvey. ;)

[Chiketkd]

I reckon if you cruised at about 80 MPH in D on a light throttle, you would see a lower signal. Not that it matters, as soon as you hit the pedal the signal would go up.
Cool. That gives me something substantial that I can loook into. Next time I hang out with Svxfiles, I'll be sure to try that. :)

-Chike

[svxfiles]

I reckon if you cruised at about 80 MPH in D on a light throttle,





These words you say, Harvey


"light throttle"




what do they mean?






Perhaps it is a language problem,





:D :D :D

[ThetaReactor]

Cruise control?

;)

[svxfiles]

Cruise control?

;)



My car has "outta control" ;)

[oab_au]

These words you say, Harvey


"light throttle"




what do they mean?






Perhaps it is a language problem,





:D :D :D

It's only for 'stock boys' Tom, you might be better to use Cruise Control, and keep the size 11s on the floor. :D

Harvey. :D

[svxfiles]

It's only for 'stock boys' Tom, you might be better to use Cruise Control, and keep the size 11s on the floor. :D

Harvey. :D

10.5D, and, yes, it's on the floor!!!!!!!!!!




BU,HAHAHAHAAAAAA!!!!!!!!

[BigBlueSVX]

10.5D, and, yes, it's on the floor!!!!!!!!!!




BU,HAHAHAHAAAAAA!!!!!!!!

...and yet another SVXer is sent to a mental hospital :eek: .




:D :p

[THAWA]

UberRoo and oab_au have it going right. What you were seeing was the duty cycle of the solenoid. Not the torque split. It is related but not the same. Subaru's official stance on the regular 4eat is a 90/10 split under normal driving conditions, and the usdm svx is a regular 4eat, and it can send as much power as 50% to the rear. So what is normal driving conditions? As you saw though it spent more time with a higher duty ratio. So it wasn't in a 90/10 condition. Suffice to say it's constantly changing, and the Select Monitor doesn't have the resolution to monitor the duty changes in real time, so what you were seeing was not all the changes. Anyway, cool topic.

[svx_commuter]

About what SVXCommuter said, about the line pressure to the Transfer clutch with the dropping resistor disconnected. This would explain the problems that some have with transfer clutch binding, when the resistor is disconnected, or if the Shift kit is adjusted too much.
In short, the TCU sets the line pressure by adjusting the A solenoid, it knows what the pressure should be, so it sends the apropreate signal to the clutch, but if the pressure is higher, due to the resistor, the clutch pressure will be higher, to cause the binding.

Harvey. ;)

Hi Harvey, :)
I really like the Subaru AWD system. I think it does what it is supposed to do. Of course the non USA system would be nicer. I am glad you posted this as sometimes I do not know if I communicate well enough and if it leads to confussion. I have actually measured the transfer pressure in my SVX. That how I found out the "C" solenoid was dead.

Take care,

John

[oab_au]

;) Hi Harvey, :)
I really like the Subaru AWD system. I think it does what it is supposed to do. Of course the non USA system would be nicer. I am glad you posted this as sometimes I do not know if I communicate well enough and if it leads to confussion. I have actually measured the transfer pressure in my SVX. That how I found out the "C" solenoid was dead.

Take care,

John

No it was a timely post John, I had not thought about it like that before you posted that. But I remembered reading a few complants of AWD binding with the fuse in, and didn't relate it to the line pressure, but that explanes it. Thanks.

Harvey. ;)
Ps. We have come a long way, since I asked you "what was in your Transfer case"? Remember mate? :D