how to: mod 1 piece torsen diff. with pictures.

[k0mpresd]

me and my friend modded his b6's 1 piece center diff earlier this afternoon.

the 1 piece diff in my b5 was the exact same as his. so all these steps are the same for b5 and b6.

i figured i would let the pictures do the talking. post any questions.





you must knock the torsen out of the housing. hit the shiny part.

[Wizard-of-OD]

What does that change the bias to?

[k0mpresd]

4:1

[D's Avant]

I wonder how this set-up would handle in the snow? Fun I'm sure, but maybe too much fun?

[BONFIRE074]

i know nothing about diff's..what exactly did you do, and what does it change? thanks

[audiness]

i know nothing about diff's..what exactly did you do, and what does it change? thanks

i'd also like the cliff notes about what this does

[k0mpresd]

changed 2 washers in the differential. this turns the stock 2:1 diff into a 4:1 bias diff.

stock diff is only capable of doing a 33/67% split between front/rear wheels. this mod will do 20/80% front/rear.

hope this helps.

[Wizard-of-OD]

I am trying to understand the mechanics of this.Your just changing 2 washers?How does that change the bias?

[Nexus1155]

increased friction from thicker washers? I love reading your threads komp good work! and Issam got my motor mounts you guys ship FAST! ;)

[djwimbo]

I am trying to understand the mechanics of this.Your just changing 2 washers?How does that change the bias?

I just wrote up everything I knew, then started looking around on the internet. Turns out I'm an idiot, but I was also interested. It's been a few years since it was explained to me.

linky

that is the very basics of it

[djwimbo]

Quote from Torsen.com
"Okay, so tell me how the Torsen differential works in non-technical jargon!

This, by far, is the most commonly asked question. The Torsen differential is simply a torque multiplier that works through the use of friction generated by thrust forces from the internal gearing. It multiplies what torque is available from the wheel that is starting to spin-up or lose traction and sends that available torque, multiplied by the TBR, to the slower turning wheel with the better traction."

EDIT: The way I look at it from the cross sections and my slight previous understanding...
Either a setup w/ a RWD as a Limited slip diff, or in our case the center diff, the outer carrier is driven. The power/torque is transferred to "side" gears and then to the "spider" gears. The spider gears are splined to the output shafts, axles, etc.
Being that the gearing inside the Torsen is a 45 degree helical cut setup, you cannot drive the carrier w/o turning one or both of the output drives(spider gears, as I'm refering to them). In the event(like I had) where there is no(0) friction/traction on the output of a driveshaft/axle the Torsen Bias Ratio(TBR) will multiply the torque by this number. Anything multiplied by 0 is 0, thus no traction, accel, and curse words.

In the event of a 0 output due to 0 traction, it would also seem to multiply the output speed by at least 2 times.

Changing the thrust washers in the spider gear axis would seem to change the preload on the gear teeth and I'm not sure still how the torque ratio is changed.

If per say in our transmission setups, the vehicle were to be placed in gear w/ the engine locked up/off/not able to rotate. The carrier of the diff would be completely stationary, and two of the wheels were on a moving surface while the other two remained sationary, the diff would bind as it then would be using one of the spider gears for input torque. The binding of the diff (presuming it was indestructable) would cause one of the following to occur.
#1 the wheels that are stationary, would no longer be stationary bur rotating, in the same direction as the wheels being forced to move.
#2 the engine would then begin to rotate, as the one output to the wheels remains stationary the side gear for that spider would be forced to turn the carrier around the spider gear. Similar to a planetary gearset.

... my brain needs to sleep. Hope that helped. The post clock is wrong, it's ~2am.

[Ian@Absolute]

increased friction from thicker washers? I love reading your threads komp good work! and Issam got my motor mounts you guys ship FAST! ;)

the washers are not thicker. they are simply minus the orange teflon coating. and they are the exact same specs as far as size is concerned.

it works off friction. dont ask me to explain how because i honestly do not understand how the diff works exactly.

this is some good reading. from this thread.. http://audizine.com/forum/showthread...ghlight=torsen

The Torsen center diff varies the torque split between the front and rear wheels by limiting the difference in rotational speed between the front and rear driveshafts. Torque from the engine causes the gears inside (in simplistic terms, half of which are connected to the front driveshaft, half of which are connected to the rear driveshaft, and all of which are in-mesh with each other) to jam together as the front and rear driveshafts attempt to rotate at different speeds, almost -- but not quite -- locking up solid until one of the driveshafts overcomes the gears' resistance to rotation (i.e., the designed bias-ratio is reached) and they begin to rotate at different speeds.

When a car goes around a corner, the front wheels travel a longer distance than the rear wheels. With an AWD car, this requires the front driveshaft to rotate faster than the rear driveshaft. Whereas an open center diff can fully accomodate a difference in the driveshafts' rotational speeds but always splits torque 50-50 between the front and rear wheels, and a locked center diff can't accomodate any difference in rotational speeds but can split torque 100-0-100 and everywhere in between, the Torsen center diff behaves like a hybrid of the two: It's never fully "open" (which is why it can vary the torque split between the front and rear wheels over a limited range) and never fully "locked" (which is why it can accomodate some percentage difference in rotational speeds between the front and rear driveshafts).

To increase the Torsen's bias-ratio -- from the OEM setting of 66-34-66 (~2:1) to say, 80-20-80 (4:1) -- all you need to do is make the gears jam together more tightly (which is what the modification discussed herein does, by replacing a needle bearing or Teflon-coated washer with a hardened steel washer, thereby increasing the internal friction that resists differentiation) and thus cause it to behave even more like a locked center diff. The tradeoff, though, is that the more you make a Torsen behave like a locked diff, the less it behaves like an open diff. In other words, by increasing the bias-ratio, you're _reducing_ the Torsen's ability to accomodate differences in the rotational speeds of the front and rear driveshafts. [I won't go into it here, but if you think things through, you'll see that under power and with all other things being equal, a Torsen biases the torque split toward the rear wheels whenever the steering wheel is turned away from straight ahead and toward the front wheels whenever it's turned back ... ponder the implications of how _this_ might affect a car's behavior while going around corners, especially if you have to apply opposite lock to catch a slide or if you keep the power on and left-foot brake!]

As an aside, it's interesting to note that with its first generation of Torsen-equipped cars (Type 44 chassis), Audi set the bias-ratio at ~3.5:1 (78-22-78) versus the ~2:1 it used with its later chassis. I don't know if this reduction in the bias-ratio was done to address NVH issues or performance/safety concerns -- some people believe the higher bias-ratio resulted in quirky handling with the Type 44 chassis under certain conditions (aka as the "Spider Bite" phenomenon) -- but there's no doubt this change did reduce the amount of "shuddering" people experience as they drive around in parking lots.

Anyway, the bottom line is that what you gain on one side of the equation, you lose on the other, and Audi chose to set the bias-ratio of its second-generation Torsen (i.e., the one with one-piece housing) low enough so that most people never experience any shudder, even if this also means settling for a less than optimal bias-ratio so far as outright performance is concerned.

(Note that there are some Audi enthusiasts -- among whose number I tentatively include myself, although I've never driven an A4 with a locked center diff so I have no actual basis for comparison -- who believe that even the 4:1 or 5:1 bias-ratio of a modified Torsen isn't high enough, preferring instead the infinity:1 bias-ratio that a locked center diff offers, not to mention the consistency/predicability of a torque split that varies in sync with front-to-rear weight transfer rather than differences in the front and rear tires' slip angles.)

[djwimbo]

the washers are not thicker. they are simply minus the orange teflon coating. and they are the exact same specs as far as size is concerned.

it works off friction. dont ask me to explain how because i honestly do not understand how the diff works exactly.

this is some good reading. from this thread.. http://audizine.com/forum/showthread...ghlight=torsen

Good stuff.
I experience shudder though. I am curious, would get worse or better? I only ever experience it during an AutoCross event at full lock(or close to) and under some throttle, never WOT.

[Ian@Absolute]

you have shudder now w/o the mod?

i get shudder at low speed cornering. when pulling out of a parking space for example. and i assume a rear lsd would make it even worse.

[Laconvail]

I should have cleaned that table off! Very easy mod and big thanks to Ian for the assistance.

[alen]

Ian, so the 2000 a4 are w/ 1piece torsen?

[k0mpresd]

correct.

[djwimbo]

you have shudder now w/o the mod?

i get shudder at low speed cornering. when pulling out of a parking space for example. and i assume a rear lsd would make it even worse.

Oh hell yea. I AutoCross my car on a regular basis and notice it every time. It's always at near full lock (I do not hold my car at full lock, ever, I'll hit it and back off a smidge) coming out of a turn as I start to roll into the throttle, sometimes before I even begin to accel.

Suspension-wise my car is bone stock OEM sport suspension, Drivetrain mods are SPEC 2+ clutch, SPEC F/W, 034 Street Mounts, and well the basic mods of Uni Stg1+ and Homebrew TBE w/ TT DP.

The shudder I feel always seems to come out of the front of the vehicle while it's trying to understeer. I know it's not the tires, and it feels like it's out of the drivetrain.
The drivetrain is stong, without a doubt, but I'm curious of what is going on. I don't think my diff has been modded before, it's a rather new thing to the B5's right? I found out only by looking that I had a 710n and a ECS "race" N75 previously installed in my car.

I haven't had my car shudder in a parking lot yet, maybe I need to spend more time in congested areas.

[airy52]

automatics suck

[soupie69uk]

Nice work, that answers most of the questions I had!!

[k0mpresd]

Oh hell yea. I AutoCross my car on a regular basis and notice it every time. It's always at near full lock (I do not hold my car at full lock, ever, I'll hit it and back off a smidge) coming out of a turn as I start to roll into the throttle, sometimes before I even begin to accel.

Suspension-wise my car is bone stock OEM sport suspension, Drivetrain mods are SPEC 2+ clutch, SPEC F/W, 034 Street Mounts, and well the basic mods of Uni Stg1+ and Homebrew TBE w/ TT DP.

The shudder I feel always seems to come out of the front of the vehicle while it's trying to understeer. I know it's not the tires, and it feels like it's out of the drivetrain.
The drivetrain is stong, without a doubt, but I'm curious of what is going on. I don't think my diff has been modded before, it's a rather new thing to the B5's right? I found out only by looking that I had a 710n and a ECS "race" N75 previously installed in my car.

I haven't had my car shudder in a parking lot yet, maybe I need to spend more time in congested areas.

see if this helps answer any of your questions. ~> http://audizine.com/forum/showpost.p...1&postcount=29

[djwimbo]

That's a good read.
So if I'm reading that the way I'm supposed to, it sounds as though the reason I'm gettin a shudder is because the rear wheels(being the higher bias) are tryin to spin faster than the front wheels. However because of the slip angles(another thing I need to learn more about), the front wheels are forced to travel a greater distance, and thus need more speed than the rear wheels to cover more ground in the same amount of time.

The idea of the inside rear wheel travelling the least amount of distance is somethign I well understand. I've been a tech for 3 years, and that's the tire w/ 75% of the punctures via, nail, screw, S&K combo wrench, etc.
Depending on the radius of the turn also depends on if the inside front wheel or the outside rear wheel is next in line for the least amount of revolutions in a turn.

the Torsen doesn't differeniate at all until the bias-ratio reaches its limit.

The way I'm translating this in my mind is that the shudder I'm feeling is due to the fact that the center diff is trying to overdrive(essentially like a separate transmission) my rear wheels and underdrive my front wheels, BUT the traction of all four wheels causes the differential to basically get confused.
The part I'm curious about, or rather haven't seen it put into words that I can comprehend, is if the Torsen varies torque application by varying output speeds, how does it compensate for loss of traction on one axle while applying torque to both? I'm still slightly confused on how steering input changes the demands to the Torsen.
I know that turning the wheels will increase the drivetrain power loss due to friction, angles, etc. and therefore require less torque/friction in the Torsen to overcome the predetermined friction coefficient in the differential.
However, if the TBR is already 2:1 and in this case the Torsen senses that there is more resistance/friction in the front axle than the rear, why would it not apply 2x more torque to the front axle than the rear? It would seem that it would essentially "sense" that ther's more traction on the front wheels than the rear if there's a higher load on the front.

The purpose of the TBR is to make some sort of figure to compare torque requirements to output correct?

I just got interupted in the middle of my thought process, so I'm all messed up now....

[onemoremile]

The Torsen can direct the majority of torque to the front or the rear. There really is no static bias since it is constantly changing. Just cruising down the freeway the car should have 50/50 distribution. Torque goes to the rear when accelerating and to the front when decelerating. What you may be feeling is the EDL trying to brake one of the front tires. It could also be related to a worn drivetrain mount.

Cars with tight diffs are interesting at low speeds. I parallel parked an Sti and it was popping and locking and making all sorts of funny noises. Nothing that couldn't be lived with but I'm sure some people would have thought the car was damaged in some way.

[fred2ka4]

Is this the same mod that STaSIS does to the diffs. that you send them or is there more to it than just changing a few washers?

Just curious as I bought the STaSIS diff off of a member who had wrecked his car a while back and I love how the car handles on the twisties now!

[k0mpresd]

basically same mod as stasis.

jared says they go about it a different way depending upon the diff. 400hpa4 says his diff was shimmed.

this mod does not use shims.

[AB18]

Is there any scientic data to back this up? I mean how do you know just by changing these washers to a dif material it goes to a 4 to 1? I am just trying to fully understand, thanks.

[ShawFM]

Is there any scientic data to back this up? I mean how do you know just by changing these washers to a dif material it goes to a 4 to 1? I am just trying to fully understand, thanks.

I think it was explained in this article. If you search Torsen T2 there is a whole lot explaining the science behind it.

[sean1.8t]

man, that does look really easy to do!

as soon as i scrape up some extra dough, im picking up these "ridiculously over priced"(haha, jk) washers!

btw, Ian, you're the man! it's really good to have you back on the forums and even better with everything you're bringing to the table. no other company, or person, that has the resources would put in the time to help the audi community out like you did. you've really stepped up. anyways, just trying to say, and i think i speak for most everyone with an audi and the modding bug, we really appreciate it!

hope to see some more tricks from you in the future.

[djwimbo]

The Torsen can direct the majority of torque to the front or the rear. There really is no static bias since it is constantly changing. Just cruising down the freeway the car should have 50/50 distribution. Torque goes to the rear when accelerating and to the front when decelerating. What you may be feeling is the EDL trying to brake one of the front tires.

I'm rollin a 98.5 I don't have EDL. I could see that being an issue though for cars that have it.

It could also be related to a worn drivetrain mount.

True, I do need to get my rear diff mounts fabbed up. Anybody ever ran solid mounts in the rear? A lot of IRS behicles have them, why don't we?

Cars with tight diffs are interesting at low speeds. I parallel parked an Sti and it was popping and locking and making all sorts of funny noises. Nothing that couldn't be lived with but I'm sure some people would have thought the car was damaged in some way.

How low speeds? Less than 10mph? If so I'm not going to worry about it.
Funny noises I can deal with, I'd love to get the DogBox when it's becomes available for the B5. I'd need a reason to get it though, AutoX and road racing don't really have a use for it.

[k0mpresd]

thank you sean.

[dingguhlbary]

even though i prob wont do stuff like this because im scared, i DEFINITELY appreciate people you like putting their time and some money into something that we all love. we all benefit from your hard work and i just wanted to say thanks for making AZ and everything a better place to be.

uhh, no homo? haha

[Siena]

Do the same modifications work in a 2001.5 S4 6-speed? (DSY / 01E).

[k0mpresd]

yes. same mod works for 01e.

[k0mpresd]

bump. check sig. ;)

[testosteronas]

k0mpresd doesn't reply PM...
Hi, everyone!
What are dimensions (outer, inner diameter, thickness) of those 2 teflon thrust washers. Interested in both T-2 01a and 01e.

[MooseWhip]

Anyone still have the pics of this?

[k0mpresd]

i have them. ill upload them later.

[MooseWhip]

Awesome, thankyou

[bryans12v]

i have them. ill upload them later.

Id love to see them too. Just seeing this for the first time.

[k0mpresd]