Traditional Limited Slip vs. Torque Bias, Please eduficate me! Options

[SirAndy]

Purpose of the car, in order:

Spirited street driving, occasional AX, occasional track days.



Here's what i think i know (IMG:style_emoticons/default/biggrin.gif)

LSD
- Always locks wheels together under acceleration and deceleration.
- Introduces understeer in slow corners.
- Generally considered the better choice for the big track.

TB
- Only locks wheels under acceleration.
- Acts like a open diff if a driving wheel is off the ground.



So, the question is, what should i get for my 915???

The car will never be a dedicated track car, it's mostly driven on the street.
The TB seems to be easier to drive on the street.
However, the slow corner understeer of a LSD could probably be tuned down with suspension settings.

The TB loses it's magick if one wheel is off the ground. In an AX setting, the suspension would need to be pretty stiff to keep both wheels on the ground at all times, would a LSD be the better choice here?


Anyone compared the two back to back in a 914?
(IMG:style_emoticons/default/idea.gif) Andy

[Joe Bob]

Only used LSDs....one came in my 915 and it's been good to me. I added a Quaife to my 901 in the Rocket....

TB needs periodic maintenance if I remember....

[pcar916]

I have run both and like the LSD better in almost all cases. Most AX'ers I know like the TBD's better because they like to snap the car through AX elements when the TBD goes open on deccel. I've always thought the deccel-oversteer in a turn with a TBD is more acute, but it does make for better slalom snaps. TBD's do one more thing that's easily driven around but it's a little annoying to me.

When I accelerate in a long sweeping turn which of course, we all do, I can feel the bias changing now and then. It doesn't seem to upset the suspension (except that I can feel it) so it's just an itch. Still, it's a little like someone tapping on their glass eye while they're talking to you.

It doesn't really effect you, but it has your attention.

The LSD is smoother and the transition from deccel to accel causes less drama. But the LSD is gonna cost more and the maintenance is higher. The clutches and plates need to be replaced now and then based on your driving style and mileage. Of course, there is something wonderful about the TBD install-it-and-forget-it thing.

There's my 2 cents. They're both good

Good luck

[whatabout1]

I have run Quaife's in my fwd rabbit, awd audi, and rwd 914 2.7 six.

The torgue biasing takes some learning but I love them. In the rabbit it would
put so much traction to the inside wheel on a corner that you had to limit the throttle
to what you could hold on to (fwd).

The awd Audi was a beast !!! If you got it fish tailing the torque transfer was scary fast.
But when/if you learned it, the beast would hook up and grab !!!
I loved racing anything in the snow (IMG:style_emoticons/default/biggrin.gif) See ya !

The rwd 914 is much the same. It puts power down on the wheel that is gripping.
It wants to understeer on the exit of slow corners. But once again the torque transfer side-to side can happen really fast. Can you say tank slapping !!!

That said I prefer the torque biasing.

[PeeGreen 914]

I forget what the difference is but I have been told by every racer up here that the TB diff is the one you want for AX. It would seem to me that if it didn't work while lifting wheels they would not have said that.

Fordahl's advice for an AX setup for a 914 is no rear sway with 200-250lb rear springs and a TB diff. I did what he suggested and my car does fine (IMG:style_emoticons/default/smile.gif)

[SirAndy]

It would seem to me that if it didn't work while lifting wheels they would not have said that.

From the Guard website:


"A torque-biasing differential performs like an open diff whenever one of the two drive wheels lifts off the ground. Lock-up and traction are lost until both drive wheels are again planted firmly on the ground."


(IMG:style_emoticons/default/idea.gif) Andy

[PeeGreen 914]

It would seem to me that if it didn't work while lifting wheels they would not have said that.

From the Guard website:


"A torque-biasing differential performs like an open diff whenever one of the two drive wheels lifts off the ground. Lock-up and traction are lost until both drive wheels are again planted firmly on the ground."


(IMG:style_emoticons/default/idea.gif) Andy

So would that mean the power is always on the ground? (IMG:style_emoticons/default/confused24.gif)

Ah, or is it so that you can get both wheels on the ground faster. I don't know. That is why I listen to the pros and do as they tell me too... (IMG:style_emoticons/default/smile.gif)

[SirAndy]

"A torque-biasing differential performs like an open diff whenever one of the two drive wheels lifts off the ground. Lock-up and traction are lost until both drive wheels are again planted firmly on the ground."

So would that mean the power is always on the ground? (IMG:style_emoticons/default/confused24.gif)

No. With an open diff, power goes to the wheel which is up in the air. Hence the wheel spin.
If the TB acts like a open diff when one wheel is in the air, the TB effectively stops working and you get the dreaded wheel spin.

(IMG:style_emoticons/default/dry.gif) Andy

[PeeGreen 914]

I guess since all the pictures of my car lifting wheels it is only lifting the front should mean I don't have the dreaded wheel spin but still interesting. Maybe this is why you do NOT want a rear sway with a TB diff. (IMG:style_emoticons/default/confused24.gif)

[Mr G Force]

You can get Guard LSD with 60 accel/ decel40 lock up. Thats what I have on the Boxster and I love it. Very little push in AX and it gives very postive feel with no lightwheel spin. I can kick both rears out

[pcar916]

You can get Guard LSD with 60 accel/ decel40 lock up. Thats what I have on the Boxster and I love it. Very little push in AX and it gives very postive feel with no lightwheel spin. I can kick both rears out

Mine is 60 / 40 as well. And you can build it with other settings without buying any more parts. I just wish it was as easy to get in and out as fast as the 911 R&P's.

[BigD9146gt]

It was my understanding that a TB ONLY works under acceleration, even when one wheel has lost grip or in the air... however from the Guard Trans quote you posted, if one wheel is off the ground its an open diff. Interesting, thanks for posting this Andy. I personally would shell out the extra $600 or so for a clutch pack diff and be done with it.

Cheers, Don.

[pcar916]

It was my understanding that a TB ONLY works under acceleration, even when one wheel has lost grip or in the air... however from the Guard Trans quote you posted, if one wheel is off the ground its an open diff. Interesting, thanks for posting this Andy. I personally would shell out the extra $600 or so for a clutch pack diff and be done with it.

Cheers, Don.

It's also true that TBD's are really stressed bad with wheel-hop.

[whatabout1]

Torque biasing will divide the power to the wheel that has traction.
IE the one that creats the most torque.

This done by gears so when a wheel lifts the torque is very quickly transfered to the
wheel with grip.

Only way to go for AX. But it does take some learning for rally (IMG:style_emoticons/default/biggrin.gif)

The TB does not care if it is acel or decel, it's just gears (no clutches).

Wheel hop always blew my CV's and never a diff.

[r_towle]

Track, Limited Slip, no question.
AX, Torque Bias for the simple fact that you can drive the car as you need to in an Autox...with a Limited slip you MUST do burn outs to get around tight corners...

Given your motor, you can use either one. Torque Bias has little to no maintenance where a Limited Slip has a clutch pack that needs to be changed and maintained...which in the case of a 915 tranny is not a simple nor a cheap thing to do...you may end up having to reset the pinion depth but I dont know how the unit is designed (like can you swap out the clutch pack from just one side???)

I would go with whatever Guards recommends...he has alot more knowledge than most people about these things...and he sells both units.

Rich

[Porcharu]

As someone who has rebuilt a lot of clutch type LSDs I can tell you for certain that they need service - really depends on how hard you drive the car. When one wheel is up in the air the only thing transferring power on a clutch type LSD is the spring pack. The stronger the spring pack is the more the 'evil' characteristics come out - like major over-steer on lift throttle corner entry - they also want to go in a straight line on power. Real racing diffs are a different story with the different ramp angles but we don't usually have that luxury in a street car. I have built LSDs with enough pre-load on the spring pack to snap axles in drag cars so they can certainly do the job.
I also drove a car for many years that had a true 'locking diff - a Detroit Locker' and would not wish that POS on anyone. In my car I am going with a helical diff - it will be used for nearly all street and some open track events. Smooth, doesn't wear out or need special oil - just works.

[turboman808]

On the street I would use a torque bias for sure. Just smooth power and doesn't remind you it's there all the time except when you need it.

[J P Stein]

I used the TB diff in my AXer If you lift the inside rear, it does act like an open diff....I hear....never done it. The TB diff transfers the power to the wheel with the most grip ( even if the inside rear is just lightly loaded) and you can feel it happen.....the car tucks tighter into a corner. If you're lifting the inside rear your suspension settings are not even close to right and you should fix that before you think about an LSD. The TB was recommended to me for AX by Fordahl, Burfield, & Guard amongst others. Nobody recommended a clutch type.
I have a TB (stock) in my MR2 turbo also. It is seamless on the street and has no problems with AX.....all stock suspension with no inside rear wheel lift....even with a rear anti roll bar.....of course AAR set that car up for Toyoda so it figures.

[campbellcj]

[campbellcj]