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Hey guys, I know our cars have AWD. Does all AWD work the same? Is it actually all wheels driving all the time? Is our AWD the same as all AWD?

What's 4WD vs AWD? is 4wd just a mode you switch into whereas we are just permanent?

It may be noobish but im just not sure the difference

Thanks!
 

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unlike 4WD, AWD kicks in when it's needed. It isn't on all the time like 4WD. Most the time I believe the car is in FWD which is why if the Haldex/Angle Gear breaks the car will have torque steer and front wheels will do burn outs :D

All AWD systems will be different (Haldex has many different Generations with VWs, Subaru has their AWD system and Bugatti I believe uses Haldex for the AWD system and Audi has Quatto system)

I don't know if all this info is true cause I'm no AWD guru.
 

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unlike 4WD, AWD kicks in when it's needed. It isn't on all the time like 4WD. Most the time I believe the car is in FWD which is why if the Haldex/Angle Gear breaks the car will have torque steer and front wheels will do burn outs :D

All AWD systems will be different (Haldex has many different Generations with VWs, Subaru has their AWD system and Bugatti I believe uses Haldex for the AWD system and Audi has Quatto system)

I don't know if all this info is true cause I'm no AWD guru.
yep thats pretty much it. and yes we have a FWD biased AWD system. so as long as they have traction, only the front wheels will drive. when your front wheels loose traction, Haldex is activated and rear wheels will recieve a percentage of your torque. im not sure on the percentage of the torque they can get, if it is possible to get a 50/50 split in the snow i dont know for sure. so no the AWD is not always activated but will when needed. this is where the collar gear comes into play!
 

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haha NO, people, you do not understand. There is no system in the world on a passenger vehicle meant for street use that all 4 wheels have power all the time. You would be shattering half shafts and cv joints left and right. There are vehicles that offer locking differentials for offroad use(this would be 4 wheels having power at all times.) Really the only difference between 4wd and AWD is the adjustable transfer case.

Source: Myself, I work with, and on Land Rovers daily. But you can search all this stuff on Google :beer:
 

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haha NO, people, you do not understand. There is no system in the world on a passenger vehicle meant for street use that all 4 wheels have power all the time. You would be shattering half shafts and cv joints left and right. There are vehicles that offer locking differentials for offroad use(this would be 4 wheels having power at all times.) Really the only difference between 4wd and AWD is the adjustable transfer case.

Source: Myself, I work with, and on Land Rovers daily. But you can search all this stuff on Google :beer:
i think you might be splitting hairs here :p to me the difference between AWD and 4WD is AWD decides when it wants to work and 4WD is on or off and usually decided by the driver. this is just a simple/general answer to the question that was asked. so the R decides when you need the extra traction and engages AWD, but if I get in my pickup and I decide i need the extra traction I will turn 4WD on and it will not turn off untill i disengage it, therefor all 4 wheels would constantly have power. :beer:
 

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The short answer for someone that doesn't know the difference between AWD and 4WD is simply "No" :D

Question 1 : No
Question 2 : No
Question 3 : No
Question 4 : No
 

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There are a whole lot of ways this gets explained and many of those ways confuse.
The FWD biased AWD is the best way to say it for our cars.
RWD biased AWD is what most of the full size pickup based SUVs use and the high line AWD full size pickups. The other of these use a system with no way to split front to rear when engaged and are the old 4WD binds up if you turn on hard pavement stuff.
The proportioning of the AWD system on R's varies. 04-05 have less initial torque to rear wheels and 06-07 have more.
The ABS/TRACS system gets in on the show and can do in some ways what non-electric locking diffs can't do: give you torque vectoring at less than 5 mph. The centrifugal activation of mech locking diffs requires more speed difference before it is active.
Volvo touts that over 95% of torque can be directed to one wheel. That statement seems to suggest disconnecting those other wheels but that is not the case. This means that if it takes 40 lb-ft to move the car and three wheels have effectively no traction (on clean ice) with a 4th with good grip then the car may send 42 lb-ft out of trans and the 40 is there at the tractive wheel to move the car. 95% of torque to one wheel sounds a lot better without all those silly details.
On hard pavement with a little initial slip the R's have 25% to each wheel.

The newest Volvos use a Haldex with full electric pump and can give full torque to rear sitting still sense no speed diff frontto rear is needed for a mechanical pump to apply force to clutch.

But to get back to the AWD vs 4WD thing. Those are used interchangeably by marketing types. Off road capable vehicles have 4WD and the same system bolted under a luxury vehicle would be AWD.
 

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no i dont. and i do understand what you are saying. the power is being distributed between 4 wheels.
lollllllll noo man!!!! At no time is power getting to more than two of your wheels at the same time.

4wd/awd = 2 wheels having power
fwd/rwd = 1 wheel having power


Understand everyone? awd/4wd only means you CAN get power to each of your wheels, you NEVER POWER ALL 4 WHEELS AT THE SAME TIME!!!


Sent from my iPhone
 

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lollllllll noo man!!!! At no time is power getting to more than two of your wheels at the same time.

4wd/awd = 2 wheels having power
fwd/rwd = 1 wheel having power


Understand everyone? awd/4wd only means you CAN get power to each of your wheels, you NEVER POWER ALL 4 WHEELS AT THE SAME TIME!!!


Sent from my iPhone
i DIDNT say EVENLY distributed. Im saying the same thing you are just in a differeny way.
 

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Why do you say you never power all 4 wheels at the same time? You do power all four. Even a conventional open diff starts with equal power applied to both wheels. If you have a wee bit of slip on an 06-07 R you have all 4 powered. If you have traction you have equal torque applied to those wheels. When there is reduced grip on one of the tires then the force goes to the slipping wheel with some wasted energy spinning the diff gears around the stopped or slowly rotating axle gear for the wheel with traction.
Only when traction is unequal or turning corners does the torque split go away from 50/50 to the two sides.
Some solid axle suspension designs like to have a lifting torque from the opposing force to the axles turning that predisposes one wheel to spin more readily but that is only the result of traction difference when the wheels have a big difference in down force to keep tire grip equal.
 

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No they don't start with equal power. it's called an "Open" differential for a reason. Traction control systems can send power to different wheels but only locking differentials can send power to all 4. There's a reason people upgrade offroad vehicles to locked differentials, because if two of your wheels are off the ground they'll spin until traction control corrects it. Power goes with the path of lesser resistance.


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Power goes with the path of lesser resistance.

EXACTLY!
When you are on the street and there is no slip and the torque applied to wheels is below the amount needed to exceed mass on tire times coefficient of friction then you have EQUAL resistance. If it was as you suspect then torque steer would make front drive cars IMPOSSIBLE to drive without hanging onto the steering wheel. You'd have grossly unequal tire wear. You'd have some weird stuff whenever the traction was more or less equal and the power was swapping side to side if only one wheel drove the car.
If the traction is substantially unequal, and even moreso when the torque applied is in excess of what is reasonably needed to move the car, then the torque goes to the easy wheel and it fails to move the car efficiently if at all.
I consulted on a locking diff 95 960 years back when that was a relatively new car. I got the case on its 4th or 5th trip back to dealer with 11K miles. Complaints in history were clunk when dropped into gear forward or reverse. Pulls to left on acceleration. The new complaint not on previous repair orders was excessive wear on right rear tire. The tire was worn down to wear bars evenly across and the left rear looked new. I was looking over car with the tech and then we drove it. The complaints were very accurate. You'd put it in gear and a delay then THUMP! Drive it and on a crowned road it would pull up the crown under power but drift a little with the crown as you'd expect with steady power.
Put it on a lift and then Had the tech go into gear with park brake locked. I could see the prop shaft spin and no wheel motion then THUMP! and the prop shaft stopped and engine would load.
I had tech release parking brake and then I pulled the cables individually with it idling in gear. I could stop the left wheel and no slowing of prop shaft. With effort I could stop right wheel and that also stopped the prop shaft. The splines on inboard CV joint inserted into axle gear were not heat treated and sheared.
The gist of this is that if power only went to one wheel you'd have load of symptoms. Power goes to both unless there is an easy path and only if there is an easy path.
I have laid two tire wheelspin marks with numerous cars and trucks that have open diffs.

Offroad vehicles will lose traction repeatedly on one wheel and overspeed a wheel and overtax a conventional cone or friction lining clutch set. The gov-lock factory fitted locking style will shear the locking mechanisms repeatedly. They put locker diffs with other mechanisms much more sturdy so they survive or weld them locked totally.

Most of the factory fitted limited slip diffs are very limited in sending power equally to both wheels when there is a huge difference in traction side to side. The main purpose of the feature is to get you moving by assuring 50-75 lb-ft of torque can go to the tractive tire instead of 100% going to the slipping tire. WHen the force exceeds the clutch limit then it goes to low traction wheel bias. When you drive a car aggressivley on the street with one of these LS diffs the traction split may only go to 45/55 when you unload thne inside tire in a turn and the limited slip can handle that and prevent the shift in torque to the inside wheel and the resulting excess wheelspin.

Let's put it this way: with open diffs the torque is applied equally to the wheels unless there is a change in the traction on one of the wheels or if the torque applied is able to overcome the grip available for one of the wheels. In these cases the wheel with reduced grip becomes the easier path of power flow. With limited slip diff the torque is distributed equally to a greater level to impede unequal distribution with traction differences side to side. With locking diff the rotational speed can be kept equal when the traction is unequal without regard to the torque applied.
 

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To the OP......

Search how a 'differential' works and you will learn which wheels get power and why.

All 4 wheels powered at the same time 'can' happen but highly unlikely, and probably for only a split second in reality.
Mathematically/on paper, yes all 4 wheels powered at the same time can happen.

But then again our engines are 900horsepower....
 

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So essentially a car has 4 wheel power until it starts moving. Ahh okay then!
Comprehension fail.

Cattlecar is spot-on.

As long as the available traction at each tire is sufficient for the amount of torque sent to that tire, then an open differential applies equal torque to each tire.

When Haldex is fully engaged, the front and rear differentials are locked together, so torque will be split 50/50 if there is sufficient traction at both axles. If there is NOT sufficient traction at one axle, then more torque will go to the axle with MORE traction. If one axle has ZERO traction, it will get ZERO torque (ignoring the torque required to simply spin the drivetrain components). This is a very ideal setup, and explains why it's used on the Veyron, Lambo Aventador, Audi R8, and countless other performance AWD cars (either Haldex or a similar design from another company).

Now looking at each axle individually, with the open differential, when one tire has insufficient traction for the torque applied, then it will slip and start to accept more torque than the tire with sufficient traction. This is NOT ideal and is what the TRACS system on these cars attempts to solve by applying the brake to the tire with insufficient traction, this transfers torque back to the tire with sufficient traction (and also absorbs some torque itself, of course, converting the power into heat in the brakes).

TRACS can not be turned off by the user short of disconnecting sensors or fuses. DSTC OFF still leaves TRACS fully operational.

I've no idea if TRACS is more or less aggressive depending on DSTC setting, I've never seen any evidence that such variance exists however.
 

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this thread took a turn.

interesting info though cattlecar, i have MT but my car does the "drift right under acceleration but drives straight with steady power" had alignment checked and all was good the Volvo shop told me the car was fine. but syptoms persisted. i may need to look into CV's
 
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