AWD and open diffs kinda defeat the perpose, no...?

coondogg

coondogg

New member
Well, short story long, I managed to get my OBS highsided on a snow bank today. The wheels were not off the ground totally but it was pretty close, lol. While I was trying to push the car down with the gf at the wheel, I got to take a look at my AWD "in action". I was kinda disappointed...

To this point (almost 1,500 miles) I've never noticed any issues with the AWD. The car does an amazing in the slippery and I've never had an issue in throttling the rear out in the snow. With the car sitting as high as it was on the snow bank, there was practically no resistance on the tires. I was visioning all 4 wheels flinging snow up in the air but that wasn't what I saw. Maybe I'm just being naive in its operation or was oblivious to this point of the open differentials but all I had was two wheels moving. Not that having all 4 wheels spinning would have helped where I was but left me with questions on the operation.

manual gearbox have a system that uses a bevel-gear center differential and a limited-slip viscous coupling that splits engine power 50/50 between the front and rear axles in normal conditions.
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While that all sounds advanced and technical, with "open" style differentials, the wheel with less traction is still going to be the one that the power is being directed through. So I guess why even equip this advanced and technical AWD with open diffs...? Guess it should be called AAWD (Almost All Wheel Drive)

 
coondogg said:
Well, short story long, I managed to get my OBS highsided on a snow bank today. The wheels were not off the ground totally but it was pretty close, lol. While I was trying to push the car down with the gf at the wheel, I got to take a look at my AWD "in action". I was kinda disappointed...

To this point (almost 1,500 miles) I've never noticed any issues with the AWD. The car does an amazing in the slippery and I've never had an issue in throttling the rear out in the snow. With the car sitting as high as it was on the snow bank, there was practically no resistance on the tires. I was visioning all 4 wheels flinging snow up in the air but that wasn't what I saw. Maybe I'm just being naive in its operation or was oblivious to this point of the open differentials but all I had was two wheels moving. Not that having all 4 wheels spinning would have helped where I was but left me with questions on the operation.

While that all sounds advanced and technical, with "open" style differentials, the wheel with less traction is still going to be the one that the power is being directed through. So I guess why even equip this advanced and technical AWD with open diffs...? Guess it should be called AAWD (Almost All Wheel Drive)
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Dear Coon:

Don't matter what kinda diffs you have...when you are beached, you are beached. Have had this happen to the rally car with locker diffs front center and rear. Don't blame the car, blame the snowbank!

 
PS...ref further to above...the bit about your diffs splitting power 50/50 in "normal conditions" which obviously does not include straddling snowbanks....

also that a center diff "spltting power 50/50" and open diffs splitting traction side to side are 2 entirely different issues.

so yes, when beached, the the standard open diffs basically give you 2 wheel drive. if there is equal traction at all 4 wheels then you have AWD

 
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Isn't this the difference between 4wd and AWD?

Also the fact the 4WD systems have a "low" mode where the front/rear wheels spin at different speeds, but this isn't really of importance in this situation.

 
Well, the story was just the background to how I noticed the open differentials. My issue is why even equip the car with the fancy dancy center differential to split power between the front and rear carriers for the carriers to only have an open differential sending power to ONE of the wheels...?

Granted that there wasnt much that would have helped me in the story other than the chain that eventually did and I guess that 2WD (AWD equipped with open differentials) is till better than one wheel drive but the "AWD" seems kinda misleading to me without being equipped with limited slip style differentials...

 
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nategr8ns said:
Isn't this the difference between 4wd and AWD?

Also the fact the 4WD systems have a "low" mode where the front/rear wheels spin at different speeds, but this isn't really of importance in this situation.
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No, not at all. A 4WD will do the exact same thing as what the OP is saying, unless it has lockers, or a healthy LSD. The biggest difference between 4WD and AWD is the AWD has a center diff that allows slip so that you can make tight turns on hard surfaces without any binding.

Also, the "low" mode you speak of doesn't make the front/rear ties turn at different speeds. It simply reduces the gearing. The only way the front and rear woul turn at different speeds is if the front a rear gear ratios were different.

 
coondogg said:
My issue is why even equip the car with the fancy dancy center differential to split power between the front and rear carriers for the carriers to only have an open differential sending power to ONE of the wheels...?
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Because it's infinitely better than having an open center diff. Without the lsd in the middle the AWD system would be like fwd when in drive and rwd when in reverse. If you ever drive a suby with an open center you'll understand how much it does.

 
2point5RS_Dan said:
Some of you guys need a refresher....

http://www.mainelysubarus.com/forums/index.php?/topic/7304-lets-have-a-discussion-about-awd-and-transmissions/

I wrote that a while ago and have a better understanding of things now, but there's still a lot of good stuff there. Watch the videos.
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words like in effect lsd, in essence LSD, or ...

get it? risiducoulous. (I don't know what I just spelled there)

hahaha.

risiducoulous

default_smile.png


anyhoo

lock up breaks things. I am disappointed too with the post 80s subes...if you aren't breaking belts in 160 hakkas sideways.. you aint got all wheel drive...or breaking centers out of steel wheels, or busting siz piece bearings like candy canes, or ripping subframes into another alignment...or popping axles, and ujoints, and steering racks, an struts...

I truly have the last of AWD subes, and without a mig welder , it is indeed impossible... the open diff stuff is to repsect the japanese tin can it is mounted to...else it will fail miserably in the steel.

the closest I have seen the racers get is very skinny wheels, being sure the terrain has no pavement..then it is back to the slippery elusive "in effect" almost LSD.

 
well modern suby diffs are NOT lockers, they are limited slip....which means even though they can lock partially on or off power (5% to 50%+ depending on application) there is still some give so you're less likely to bust stuff

 
Why would you want to break things? And lockup DOES NOT break things if you don't use it in stupid ways.

The first time I landed my Legacy in a snow bank I too was upset that all 4 wheels weren't turning. I thought my car was broken.

 
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