Manual VS Auto for AWD

[jasinwa]

Putting aside stick vs. automatic (I like stick myself, but my wife wants me to buy auto. so she can drive my car!!).....

 

Does anyone have an opinion ( ) about which type of AWD process is best, the one used in sticks or automatics?

 

thx...

[cookie]

They both do the job. My Forester has been a winner in the mud for me with a stick, and I hope MT Smiths chimes in. He lives with a steep snowy driveway and says his automatic could outperform his stick in the snow.

[mtsmiths]

They both do the job. My Forester has been a winner in the mud for me with a stick, and I hope MT Smiths chimes in. He lives with a steep snowy driveway and says his automatic could outperform his stick in the snow.

 

Here I am. And yes, we've had four Subarus (two GL-10s and two Legacies) while we've lived with our steep snowy driveway in Whitefiish, and we drive a LOT in deep snow, because we are on the low priority plow routes. I find the AT to deliver smoother power and far less likely to spin than the MTs.

 

'Sides, I'se gettin' old and lazy.

[NorthWet]

I discovered that the manual will not move with the rear driveshaft removed (for towing) while the auto will. This *may* translate to what happens when one rear wheel slips.

[Manarius]

For the MT's, the AWD is 50/50 all the time. With the AT, there's a solenoid to transfer power.

[idosubaru]

on newer generation Subaru's (EJ) the manual trans do not have the option to lock the center diff. BOO for SUBARU for not keeping that trait of the older generation models. for automatic trans subarus you can install a duty solenoid C switch and control lock up of the transfer clutches for the rear. this will essentially "lock" the front and back, the car will hop and jump like a truck in 4WD. can't do that with the manual trans, the center diff will always remain open.

 

on older model manual transmissions (EA, ER series vehicles) they offered locking center differentials and even dual range. those are great vehicles in terms of 4WD capability.

[NorthWet]

For the MT's, the AWD is 50/50 all the time...

Slightly OT, and not wishing to start a discussion/argument, but this is technically not correct. It is 50/50 until the viscous coupling gets involved, and then the "split" shifts in favor of the non-slipping wheels. Technically, a vehicle with an open center diff that has one wheel spinning and all others sitting still has a 50/50 torque split.

[Manarius]

Slightly OT, and not wishing to start a discussion/argument, but this is technically not correct. It is 50/50 until the viscous coupling gets involved, and then the "split" shifts in favor of the non-slipping wheels. Technically, a vehicle with an open center diff that has one wheel spinning and all others sitting still has a 50/50 torque split.

Mmmph, I was pretty sure that the 5MT's were 50/50 all the time due to the viscous coupling - but, we learn something new every day.

[nipper]

Ive had both, i like the automatic. There is a misconseption with the manual. The manual has to have some slippage to get the 50/50 split. The automatic uses a computer(and solenoid), two speed sensors and an internal spool valve to figure out when where and how to apply the AWD. The newer systems are also more responsive do to G sensors. The autpmatic will give better handling when the car is pushed to the edge, but that doesnt matter in normal agresive driving.

The automatic tends to get more torquebind if its not maintaned. the manual doesnt get it as much, but when it does, just write a big check. Manual will give you better gas mileage.

 

nipper

[MountainBiker]

Mmmph, I was pretty sure that the 5MT's were 50/50 all the time due to the viscous coupling - but, we learn something new every day.

No, the manuals are 50/50 due to the DIFFERENTIAL, not the VC. The Auto doesn't even have a center differential.

 

Remember driving a rear wheel drive car or truck and spinning one wheel? Those vehicles have a 50/50 split between the rear wheels due to the differential, and what good does it do you?

[nipper]

No, the manuals are 50/50 due to the DIFFERENTIAL, not the VC. The Auto doesn't even have a center differential.

 

Remember driving a rear wheel drive car or truck and spinning one wheel? Those vehicles have a 50/50 split between the rear wheels due to the differential, and what good does it do you?

 

 

Ok time ot get technical. If the car only had a center differential you can have 1 wheel drive. All the power can go to the wheel with the least resistance, thats the weakness of a differental. The VCD adds resistance to the center differentail so that when there is a speed differnce between front and rear, it in essance locks the center diff, to allow for 50/50 split os power to front and rear.

 

nipper

[MountainBiker]

And a little more technical. The VC never really "locks". It requires a speed differential to start doing much, which I've found to be a couple of tire revolutions of the slipping wheel on the front axle. Then one of the rear wheels starts spinning, but at a little slower rate than the spinning front wheel.

[nipper]

And a little more technical. The VC never really "locks". It requires a speed differential to start doing much, which I've found to be a couple of tire revolutions of the slipping wheel on the front axle. Then one of the rear wheels starts spinning, but at a little slower rate than the spinning front wheel.

 

even more technical the vscous coupling is made of altenating plates with calibrated holes in them. This all sits in a viscous fluid. The spinning plates at differnt speeds shear the fluid, creating friction, which causes heat. The fluid as it gets hotter becomes thick and transmits power. The size of the holes in the discs determines when this happens.

 

nipper

[ferret]

Preface this...Subaru's AWD systems are wonderful. Both different. Both require matched tire sizes and tire maintenance ( air pressure and rotation ). There are many out there driving Subaru's with non-functioning or damaged AWD systems and don't know it. (Center viscous coupling defective, Duty-C solenoids gummed up so they can't control clutch engagement pressures, Center couplings BAD from tire mismanagement)

 

I've owned both. I prefer the manual, My wife the automatic.

 

Manual starts in a 50/50 split. Driving it in the snow feels more like a RWD and handles like it. I can fishtail around corners if I give it a little more gas, but the front will take over.

It is ALL mechanical and requires a small amount of wheel slippage to 'shear' the fluid. AND YES the transfer changes from 50/50. But no driveline bang or clunk like when the duty solenoid engages the rear on an automatic.

 

Automatic starts in FWD mode. When it detects slippage, and YES a wheel here can turn for a second or 2 in the snow depending on speed, condition or just the turned steering wheel where the open differentials are only turning their input shafts back to the tranny at a fraction of the other side, then the TCM via input from the front and rear speed sensors, will pulse the duty solenoid to lockup the front and rear drive shafts up to a 50/50 split. Any more spin than that 1-2 second and your automatic is not AWD anymore. Also an early 90 Legacy manual stated you would stay locked in AWD until the vehicle speed fell below 7 mph or some low speed like that.

 

I attached 2 .pdf file from the current service manuals. As you peruse the automatic one, it refers to VTD. This was for turbo-charged cars only. So your non-turbo Legacy or Outback does not work this way.

03._Center_Differential.Pdf

11._Awd_Transfer_System.Pdf

[jasinwa]

I thought auto started in 90/10 mode.....not total FWD...

 

I live in the Seattle area and on a steep hill, if that makes a difference...

[nipper]

I thought auto started in 90/10 mode.....not total FWD...

 

I live in the Seattle area and on a steep hill, if that makes a difference...

 

auto runs from 90/10 all the way through to 50/50, and it is constantly varying.

 

nipper

[subie94]

ever since getting my first 5spd,i never looked back(cept a small mix up a yr back)

 

though at times,i feel lazy and want a auto..

 

 

i'll keep my 5spd

[NorthWet]

and not wishing to start a discussion/argument....

(deep sigh)

I am sorry that I brought this up. There is a general misunderstanding of the meaning of the term "torque split", so any discussion of this seems to start an argument. Any discussion of what has how much torque split falls into meaninglessness because of this.

 

50/50 split means that if one wheel slips then the others will essentially stand still: Small amount of torque (maybe 1-5ft-lbs) to keep the wheel slipping and THE SAME FORCE to the other wheels. All of the rest of the "power" doesn't exist; an engine in neutral at 4000rpm isn't transmitting any power, and an engine spinning a wheel with an open diff isn't developing any more power than to spin the wheel.

 

A vehicle with a locked differential/transfer-system can have a 100/0 (or 0/100 split). Simple (2WD) example: Welded rear end, one axle pulled so 0-torque goes to that wheel and all the torque goes to the other wheel. The auto's transfer clutch pack is capable of 0/100 (3AT allows a "lock" by nature, 4EAT if the TCU allows it), as is the FT4WD manual boxes with locking diff.

[jon38iowa]

Ok time ot get technical. If the car only had a center differential you can have 1 wheel drive. All the power can go to the wheel with the least resistance, thats the weakness of a differental. The VCD adds resistance to the center differentail so that when there is a speed differnce between front and rear, it in essance locks the center diff, to allow for 50/50 split os power to front and rear.

 

nipper

?

Does anyone know how much these unique parts(VCD, Solenoid) cost and whats the typical service life?

John

[nipper]

?

Does anyone know how much these unique parts(VCD, Solenoid) cost and whats the typical service life?

John

 

Man do we know what they cost, they range from 800-1200 depneding upon location. I've heard some rediculous prices for VC from some bad dealers. My awd unit was 950 at 185,000 miles so im not complaining, thats a good run. Service life for the wuoto seems to be anything over 180K (educated guess) but can go far beyond that. On the manual till you drive on your first flat. The auto as long as the fluid is changed regularly they seem to last.

 

nipper

[cookie]

Thinking about what MT Smith has said about the controllable power delivery of the automatic reminds me of my last Jeep. I have had several Jeeps with both stick and auto.

The last one was a CJ7 with a rare turobo 400 automatic and a transfer case with clutches like and automatic Subaru. I bought it when my manual Chevy S10 was a pain in the butt pulling my heavy sailboat up slippery SSF boat ramps. The Jeep just dropped into gear and the torque converter gives you about 40 to one advantage. It would just idle up the boat ramp withoput spinning a wheel.

My five speed Subie goes through the mud well but there is some drama involved and I get to clean a lot of mud off later thrown by all four spinning wheels. I have to keep speed up to make it through. I'm sure if I had actual traction ony two wheels would spin but when they are all somewhat free look out.

[nipper]

Thinking about what MT Smith has said about the controllable power delivery of the automatic reminds me of my last Jeep. I have had several Jeeps with both stick and auto.

The last one was a CJ7 with a rare turobo 400 automatic and a transfer case with clutches like and automatic Subaru. I bought it when my manual Chevy S10 was a pain in the butt pulling my heavy sailboat up slippery SSF boat ramps. The Jeep just dropped into gear and the torque converter gives you about 40 to one advantage. It would just idle up the boat ramp withoput spinning a wheel.

My five speed Subie goes through the mud well but there is some drama involved and I get to clean a lot of mud off later thrown by all four spinning wheels. I have to keep speed up to make it through. I'm sure if I had actual traction ony two wheels would spin but when they are all somewhat free look out.

 

torque converters multiply torque 2:1. Automatics actually seem easier to deal with in alot of situations then manuals.

Only time a manual is better in special situations is when you can engage the starter in low gear to help you get out of a bad situation instead of using the clutch.

 

nipper

[cookie]

Is it really 2 to 1? I saw the 40 to one number on a Jeep board a few years back and I have always trusted it. Does this mean I can't trust everything I read on the internet?

[nipper]

Is it really 2 to 1? I saw the 40 to one number on a Jeep board a few years back and I have always trusted it. Does this mean I can't trust everything I read on the internet?

 

heheh look up torque converter on the net, its 2:1 and they have gone as high as 3:1,2;1 thats the number its been for since the things have been invented. Thats the reason VW semiautomatics didnt really have 1st gear, and powerglides only had two gears, the torque converter is so good at multiplying torque its not needed

http://auto.howstuffworks.com/torque-converter1.htm

http://www.drive.subaru.com/Fall02_TorqueConvert.htm

http://www.tciauto.com/tech_info/torque_converters_explained.htm

 

nipper

[cookie]

The author of that other article may have meant with the transmission and low range on then. Perhaps you could get down to that torque multiplication then but these articles indicate the the torque converter cannot do it alone.