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Torsen vs standard Traction lok LSD differential pros and cons?

FreePenguin

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There is no oil filter. Clutches are carbon fiber, there's also a load 's' spring in there. It's a very strong design.
123950462_3501399163288357_1278219605870280793_o.jpg
now I want one just because it looks cool inside lol
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Norm Peterson

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The torsen doesn't 'lock' at all, and neither does the clutch pack. The standard limited slip is an open diff with clutches on the outputs that minimize relative wheel speeds beyond what the open diff would allow for.
That's not quite the way I understand those things. With preload (that 'S' spring), the differential wants to be locked up until the preload is overcome by the wheels having to run on different radii. Then it 'sort-of' goes open still against the friction that 'wants' the axle shafts to run at the same speed. I think it's possible to use ramps to force tighter clutch pack compression and greater resistance to the axle shafts rotating at different speeds.

This preload makes clutch (and probably cone) style limited slip diffs inherently somewhat understeerish during corner entry relative to an open diff. And I suspect more understeerish on entry relative to a Torsen at least during neutral throttle conditions. There's probably a difference in driving technique involved.


Norm
 

Brian@BMVK

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That's not quite the way I understand those things. With preload (that 'S' spring), the differential wants to be locked up until the preload is overcome by the wheels having to run on different radii. Then it 'sort-of' goes open still against the friction that 'wants' the axle shafts to run at the same speed. I think it's possible to use ramps to force tighter clutch pack compression and greater resistance to the axle shafts rotating at different speeds.

This preload makes clutch (and probably cone) style limited slip diffs inherently somewhat understeerish during corner entry relative to an open diff. And I suspect more understeerish on entry relative to a Torsen at least during neutral throttle conditions. There's probably a difference in driving technique involved.


Norm
That's not my experience of how it operates. The trak lock actually had less corner entry understeer than the torsen does, but that didn't make up for the improvement in grip and torque biasing yaw on power the torsen has.
 

Norm Peterson

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Is that due to a difference in corner entry technique specifically for autocross, or is it more generally?

Everything I've read about Torsens that mentions corner entry at all says something like "easy turn-in at corner entry", which makes sense if you're not doing any leading throttle that early.


Norm
 

CorvZ061

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I have noticed a few things about my torsen, when I turn into my grand mother’s driveway, it’s a steep up hill from a flat road, the car doesn’t flex much so it picks up the rear inside tire, when it does that there’s no preload for the diff so it only spins that tire so no forward movement. I do get the wheel hop feeling at a low speed sharp turn, like turning onto a main road from a stop.

My Eaton Trutrac in my Chevelle, another gear type lsd, doesn’t do that turning into her driveway, it’ll lift the inside wheel and the outside will pull the car up, though I’m sure that’s not good for it. But the manners of that trutrac on the street aren’t nearly as good as those of the torsen, you can feel it transfer power rather harshly at times.
 

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Brian@BMVK

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Is that due to a difference in corner entry technique specifically for autocross, or is it more generally?

Everything I've read about Torsens that mentions corner entry at all says something like "easy turn-in at corner entry", which makes sense if you're not doing any leading throttle that early.


Norm
I'd say in general, but more specifically autocross where the relative speeds between the inside and outside is/needs to be larger due to corner radius. The torsen bias ratio goes both ways, and has the opposite effect off throttle/engine braking. We saw this rear its ugly head with our Formula SAE car when experimenting between the 4:1 and 2.5:1 setups for the torsen. 4:1 is awesome on throttle but it does induce entry understeer.

The clutch pack never had that kind of behavior off-throttle and was the only thing that was "better".
 

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I'd say in general, but more specifically autocross where the relative speeds between the inside and outside is/needs to be larger due to corner radius. The torsen bias ratio goes both ways, and has the opposite effect off throttle/engine braking. We saw this rear its ugly head with our Formula SAE car when experimenting between the 4:1 and 2.5:1 setups for the torsen. 4:1 is awesome on throttle but it does induce entry understeer.

The clutch pack never had that kind of behavior off-throttle and was the only thing that was "better".
I wrote a long thing a week or 2 ago on diffs that I'm not going to try to repeat, but some of what you felt concerning the Torsen and Trac-Loc was probably because they have the same bias ratio on coast and drive. When you get enough locking on one side it will be too much for the other. A clutch pack differential with different ramp coast/drive angles is much different than one that just uses the spreading force of the side/pinion gears. It allows much higher bias ratios and the ability to separate corner entry/exit.
 

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I wrote a long thing a week or 2 ago on diffs that I'm not going to try to repeat, but some of what you felt concerning the Torsen and Trac-Loc was probably because they have the same bias ratio on coast and drive. When you get enough locking on one side it will be too much for the other. A clutch pack differential with different ramp coast/drive angles is much different than one that just uses the spreading force of the side/pinion gears. It allows much higher bias ratios and the ability to separate corner entry/exit.
The Trac-Loc just doesn't have a strong bias ratio in general, so it feels a bit more like an 'Open' diff on coast, particularly with 70k mile heavily used clutches.
 

TeeLew

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The Trac-Loc just doesn't have a strong bias ratio in general, so it feels a bit more like an 'Open' diff on coast, particularly with 70k mile heavily used clutches.
I don't remember how many 'traction events' they're supposed to be good for, but it's not many.

A long time ago, if you were racing with a Trac-Loc, you'd take a sanding disk to get the friction material off of the clutch plates. This would make the clutch pack steel on steel (better for longevity) and allow you to put (I think?) 2 extra plates per side (increased bias ratio/locking). It was also common to try to expand the 'S' spring to give more preload, which made it a bitch to get installed.
 

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I'm going to log all 4 wheel speeds on my AccessPort during AX runs this weekend to try to understand the differential and anti-lock systems a little better. I'll report back.
 

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That would be great. I'm looking forward to it. :like:

Anyway, racing aside, for street driving I like the Trac-LOK. It's very smooth, no clunks, no wheel hop, no nothing, and when I give it some beans in a tight corner I feel like the whole car rotates around my hips. It's an awesome sensation. I love it. I often accelerate on corner entry precisely to get this effect. This may be a no-no in a race, but on the street, at low speeds, it feels awesome.
If I mash the throttle in a straight line the car does tend to fishtail a bit. I guess that's something all LSDs do, but is the Trac-LOK more prone to it than the Torsen, or the other way around? I have a hunch that the Torsen may be more prone to that. Is it?

I was initially planning to replace my Trac-LOK with a Torsen, but now I'm not so sure anymore. Not only does the Trac-LOK seem to work just fine in real life, but the more I read and understand about its inner workings, the more impressed I am with its simple but solid design.
 

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If I mash the throttle in a straight line the car does tend to fishtail a bit. I guess that's something all LSDs do, but is the Trac-LOK more prone to it than the Torsen, or the other way around? I have a hunch that the Torsen may be more prone to that. Is it?
No. If the car is fishtailing in a straight line, either the road isn't actually straight, has heavy crown, or you have an alignment discrepancy left to right.

On corner exit, the torsen is far easier to control throttle-induced yaw.
 

ice445

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That would be great. I'm looking forward to it. :like:

Anyway, racing aside, for street driving I like the Trac-LOK. It's very smooth, no clunks, no wheel hop, no nothing, and when I give it some beans in a tight corner I feel like the whole car rotates around my hips. It's an awesome sensation. I love it. I often accelerate on corner entry precisely to get this effect. This may be a no-no in a race, but on the street, at low speeds, it feels awesome.
If I mash the throttle in a straight line the car does tend to fishtail a bit. I guess that's something all LSDs do, but is the Trac-LOK more prone to it than the Torsen, or the other way around? I have a hunch that the Torsen may be more prone to that. Is it?

I was initially planning to replace my Trac-LOK with a Torsen, but now I'm not so sure anymore. Not only does the Trac-LOK seem to work just fine in real life, but the more I read and understand about its inner workings, the more impressed I am with its simple but solid design.
Its a classic design that works well, even if it's not as good in a racing application. For street use I wouldn't bother upgrading. The units are pretty cheap to replace too once they wear out. You can get two or three trak lok rear pumpkins for the cost of one Torrent unit lol
 

Norm Peterson

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Anyway, racing aside, for street driving I like the Trac-LOK. It's very smooth, no clunks, no wheel hop, no nothing, and when I give it some beans in a tight corner I feel like the whole car rotates around my hips. It's an awesome sensation. I love it. I often accelerate on corner entry precisely to get this effect.
That's exactly the kind of abuse that wears the clutches or cones out in those styles of limited slip diffs in track driving. Just that you may not be pushing as much power through everything as you would while racing or driving at near race-pace at HPDE on the track, so wear rates would tend to be somewhat lower.

Trac-loc and similar limited slip diffs can also cause increased rear tire wear rates if there's much bias. The force required to make the limited amount of slip happen and permit normal cornering ultimately comes from increased longitudinal contact patch forces.


Norm
 

Norm Peterson

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I wrote a long thing a week or 2 ago on diffs that I'm not going to try to repeat, but some of what you felt concerning the Torsen and Trac-Loc was probably because they have the same bias ratio on coast and drive. When you get enough locking on one side it will be too much for the other. A clutch pack differential with different ramp coast/drive angles is much different than one that just uses the spreading force of the side/pinion gears. It allows much higher bias ratios and the ability to separate corner entry/exit.
Saw that.

It's part of what leads me to believe that driving with a Torsen might take a slightly different approach to use of the throttle at various stages of your cornering, and perhaps a little rework with bar and/or damper settings if adjustments to those is available.


Norm
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