Is the Subaru the only true AWD at all speeds... I was reasding up websites and the Honda/Acura AWD system only engages when required, so does Ford Escape, VW, Infiniti etc... Did not research all vehicles... but looks like the Subaru is a better system... No wonder I can never skid my Forester and could skid my A6 in extreme conditions turning in snow... Any thoughts/clarifications on this???

i know the older Quattro systems that had user lockable rear diffs automatically unlocked after 15MPH or so. I would say that is still true today with the "auto" systems.

I think what happens with the Torsen system is at speed the center diff unlocks - so power is sent to front or rear; but once one end starts to slip it then locks back up????

The torsen center diff is mechanical and works at any speed.

However the "locking" front and rear diffs are really the application of the slipping wheels brakes. Many cars have a limit to the speed, which this can be supported due to the limitation of the ABS system. So, a while ago the speeds where relatively low, but now they have generally increased.

Another data point is the stability control also uses the brakes to control roll and yaw of the car. If you remember stability control was optional on the TT when it first came out, but after a couple of high-speed deaths it became standard.
So I would assume is stability control can work at high speeds so can ABS and so does the "locking" diff for Quattro.

On a personal experience. I braked very hard while going 100 mph in my 99 A6q and the ABS did kick in.

But the bottom line is that I do not truly know.


Russ
97 A6qw

The locking rear differential on pre-96 cars was manual and would unlock at 15 automatically. I think the 96+ rear EDL works at higher speeds. But the torsen works the same at 100 MPH as it does at 10 MPH. It constantly varies the torque between the front and rear axles bases on which one it turning slower.

Go here
http://www.ibiblio.org/tkan/audi/usmodels.html

Look at the bottom of the page.

Rokas

and it works on all speed. EDL locks rear diff. and it works only on low speed (<25mph) because you need it only if you in really bad snow/ice. If you will lock rear differencial on high speed you most lickely will loose control of the car.

Subaru has two absolutly different AWD system for manual and auto transmission. I used to have Legacy Turbo with 5sp. Nice car and AWD really nice, but Audi Torsen is better IMHO.<ul><li><a href="http://home.attbi.com/~eliot_www/awd.html">here is nice link</a></li></ul>

it is a device which as a result of the worm and gear 'drive but not driven' principle, is capable of sending drive to bothe axles even if one is slipping. If a normal diff were used when one wheel looses traction, all the drive will go there. The torsen diff is capable of coping with the speed difference between front and rear when cornering and due to slight variation in rolling diameter of the tyres but it will not allow all the available torque to go to the slipping wheel. The only weak part in the system is is you have a car which did not have a lockable rear diff but was not new enough to be fitted with EDL. Then you could get stuck on snow or ice, this does not effect the system in normal driving though where neither EDL or manual diff lock are required.

No offence, but the 4EAT automatic in your Subaru is junk compared to the Torsen. The Subaru uses a clutch pack as the center diff. There is a front and rear speed sensor, when the computer detects a speed difference from front to rear then the clutch pack is pressurized (engaged) or unengaged to send power to the front or rear. The 4EAT is notorious for "Torque Bind" be sure you always replace tires in sets of 4, I think a difference in tire circumfrance of 1/4" from front to rear will cause pre mature wear on the clutch pack.

To sum it up the Torsen is bullet proof and with a lockable rear diff. You can moto through some pretty serious stuff. The Subaru system is vonerable and without a lockable differential you don't have as good a chance of making it through.

According to this the Subaru's Viscous Coupling Differential Lock is better that Audi's quattro<ul><li><a href="http://autozine.kyul.net/technical_school/traction/tech_traction_4wd_2.htm#Torsen">http://autozine.kyul.net/technical_school/traction/tech_traction_4wd_2.htm#Torsen</a</li></ul>

A friend of mine has a manual subaru, and I have always been surprized by his stories of slipping and then feeling the rear axle getting traction and straighten the car out. For having fun the subaru sounds better. But for going down the road in the direction I want, I will take the quattro.

Russ
97A6qw

It says that Torsen dissadvantages are cost, and does not have the ability to split torque.

The Subaru system they are refering to is only in the manual transmissions. The 4EAT AWD system I was refering to in my earlier post is found in the automatic Subaru transmissions, and it's not very good.