# Quattro center diff - housing and Torsen questions/discussion



## DHill (Jan 8, 2002)

Point of thread: Show me some Quattro transmissions, real ones. Please?
Background: 
Over on the VWVortex Quattro/Syncro/4Motion forum there has been a lot of discussion about the function of a Torsen differential. A lot of the Syncro guys would like something that puts power to the rear a little faster and stronger than a viscous coupling, so the current thing to do is swap in the Haldex limited slip coupling with stand-alone electronics to run the thing.
While a viscous coupling really only has an input and output, a Torsen differential is usually driven via the housing, i.e., using a ring gear, perhaps a chain-driven sprocket, or in the case of the A4, apparently there is an input shaft sleeved over one of the output shafts, making a compact assembly for the Torsen center diff to split torque front/rear. The housing is the input, and the two output shafts drive the front and rear drive axle shafts, respectively. 
However, there are still a few holdouts. From looking at hundreds of images and staring at the differential, it seems that it cannot be used as anything other than what it is... a differential. What would be great is if you could unbolt the viscous coupling on the Syncro rear axle, and then bolt up a Torsen diff, therefore having a direct gear-gear connection and better control of traction. 
So what would be great to see here is any pictures of Quattro transmissions opened up, exposing the Torsen diff and its interaction with the rest of the gearsets. A friend of mine over there has shown me a few ETKA drawings of his A6 transmission, and from them I do not see how the Torsen housing is driven. I told him it uses the sleeved shaft design, to my best guess, but he doesn't buy it. Can someone show me a real transmission to put this to bed???? TIA!








Pictures for reference:
*Syncro* Note the viscous coupling (cylindrical thing in front of rear diff with ribs in the casting). The clutch plates slip in the viscous fluid to transfer torque between shafts. Distributes torque to the rear axle when the front wheels slip, thus Syncro is "part time" AWD. Works best for transverse-mounted engines designed typically for FWD service. 
























Syncro transmission. Much like a normal FWD transaxle, there is an additional transfercase which splits torque to the center propshaft via a bevel gear.
















Here's the Audi A4 cross section that revealed to me that one of the output shafts on the Torsen can be sleeved to the Torsen housing input shaft.








The Torsen diff, for those that don't know:








*How it works:* 
Mesmerize yourself by staring at this diagram:








Ignore the arrows for the moment.
1) Rotate the shaft on the left counter-clockwise (CCW) - I like to pretend I'm turning it with my left hand.
2) The helical gear (splined directly to that shaft - just inside the housing) will now be rotating CCW.
3) The top Invex gear (or worm gear) is now rotating CCW about its journal pin (the pin through its axis).
4) Since that Invex gear is rotating CCW, the one right next to it is rotating clockwise (CW). 
5) Since that Invex gear is rotating CW, so is the helical gear (on the other side) to which it is meshed. Thus, the other shaft is rotating CW.
Ta da! CCW on the left = CW on the right.


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## TORSEN TRACTION (Mar 27, 2002)

*Re: Quattro center diff - housing and Torsen questions/discussion (DHill)*

Hey, you are right about the Torsen not working when mounted like a coupling. If you want to make it more RWD then I would think a more agressive viscous coupling should take place of the stock unit. 
As far as trying to modify the transaxle it wont work because of the space you have to work with and it would be tricky.
I have seen a few cut away transmission pics. They are pretty much the same layout. here is a pic of the Audi ZF 6speed automatic.


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