2015+ S550 Mustang Forum (GT, GT350, GT500, Mach 1, Ecoboost) - Mustang6G.com 173 - AWE - 1
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Transmission & Drivetrain Everything related to transmission, drivetrain, gears, etc.


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Old 01-06-2017, 02:18 PM   #61
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I know this isn't directly the OP's original complaint here, but - I know any number of Mustang track racers who really don't care much for the factory street Torsen for track use. There's a fair bit of personal preference involved in how much and when you want your diff kicking in, depending on your cornering style. Of course, Torsen and others offer more hardcore stuff for the track, like the Race High Bias 4.0 version that came in the FR500's. Then there's the Wavetrac that works in loaded and unloaded conditions both, and tend to be a bit stronger than the Torsens. There are many, many others that do a lot of different things.

So - don't feel bad if the Torsen isn't your cup of tea. You are not alone, and there's plenty of help out there.
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Old 01-06-2017, 02:22 PM   #62
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Quote:
Originally Posted by TexasRebel View Post
So the torque being transferred from the diff. case, through the parallel gears, and to the axles is what forces the parallel gears into the sides of their pockets? I thought the action of differential torque applied to the axles forced the floating parallel gears outward, away from the helical gears on the axles, into the pockets. More torque differential, more normal force, more friction (as well as more parallel pairs, and larger diameters, and different pitches, &c.)



Nah. I painted the tops of my tires once after I reclutched an Eaton Posi on my C10. Without any weight in the bed those marks almost never moved. Everything went into increased tire wear.






I'm in that grey area of being and OEM customer (well, designer technically, but that's how parts end up in OE specs) as well as an end user in my free time. You've still avoided my post #45 question.
Not avoided, just lost it in the swarm of other comments/questions. Is the answer not already apparent?

Anyway, torque flows into the diff housing (case) from the ring. The rotation of the housing transfers torque into the planet gears, which are journaled in bores within the housing, so they are forces to revolve around the center axis with the housing. As the PGs are driven around under torque load, they're in mesh with the side gears, and push them around as well, thereby transferring torque from the PG through the SG, to the axle shaft and out to the wheel. When torque flows through the gears as such, the actual force loads at the mesh points have reaction forces, which push the gears apart.

The combinations of these force reactions - from PG to PG and PG to SG - generate multiple thrust forces. The PGs are pushed somewhat radially, the SGs axially. The gears are pushed into the housing, and contact surfaces between them is where the friction is generated. As torque is increased, the loads increase proportionally. So as torque is increased, the total friction increases. That's why, with no load, it differentiates freely and above the performance torque threshold, it won't differentiate at all.

Anyhoo, back to your previous question, I've been doing this for long time. So, if it I run right past something that I think is obvious (but isn't), let me know. I have been a design/test/development engineer, occasional vehicle dynamics engineer and some-time sales engineer for Torsen products for just short of 20 years, so its easy to forget that normal people don't always make the same assumptions I do...
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Old 01-06-2017, 02:24 PM   #63
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Pardon my dumbass question amidst a sea of technical talk, but would the Torsen contribute to my right rear tire wearing out much faster than my left? Tire guy said it didn't look alignment related and that it was due to the diff.
http://www.mustang6g.com/forums/showthread.php?t=60375

could be a factor.
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Old 01-06-2017, 02:30 PM   #64
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I'm not sure how, off hand. If the axle differentiates freely, then I can't think of why it would contribute to one side alone. If the diff were binding, you'd probably see both tires scrubbing because they'd be more locked together. Unless you do a lot more turning to the left, and put more load on the right. I will offer that the driveshaft torque tends to lift the right side and plant the left (that's why open diff cars almost always spin the right side), but that tendency is much pronounced compared to live axle cars. I'd have to imagine its tied back to something specific to what's controlling the wheel/tire on that side.
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Old 01-06-2017, 02:41 PM   #65
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I have been a design/test/development engineer, occasional vehicle dynamics engineer and some-time sales engineer for Torsen products for just short of 20 years, so its easy to forget that normal people don't always make the same assumptions I do...
Nice! I'm in year 3 designing underground construction equipment and accessories. Came from designing agricultural equipment for research (University, graduate research). Right now my scope is so broad I'd love to narrow it down to focus on one type of component. In this "Jack of all trades, master of none" world I know just enough about a lot of different things to get into way too much trouble.

...so when does the Torsen T2 get a sliding shaft between the splines of the two sun gears to lock up on demand?
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Old 01-07-2017, 06:04 PM   #66
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Originally Posted by BmacIL View Post
Now that's tempting...

Send me a PM if your interested.
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Old 01-11-2017, 03:18 PM   #67
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I came across this video today. While it touches on the basics of how a Torsen works, it shows a T1, not a T2.

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Old 01-11-2017, 03:43 PM   #68
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That video is also pretty much incorrect. The whole worm wheel/gear theory, acting like a self-locking gear set, is great and very popular. It is also not true in general practice. FWIW, I can tell you that the man that invented the layout truly believed it, but that doesn't change the basic situation.

The gear geometry isn't nearly severe enough for that principle to work (even in their rendering, its not suitable). The helix angle of the side gears needs to be around 80 degree or so to be able to prevent worm back drive, but in practice they're usually in the 45-50 degree range. So instead, the gears roll across each other, albeit with a bit of friction added due to the partially sliding mesh. So, it would still free spin if a wheel was unloaded. That's not to say that such a design couldn't work if the geometry were changed, but such a high helix angle would trade away substantial strength as well as driving dynamics. Consequently, no one makes them that way.

With all of that said, even if the geometry of the crossed-axis design (Type-1) were such that it would prevent back driving, none of this has any real bearing on the Type-2 parallel axis design that's used in almost all Torsen applications (including S550) today. I do appreciate the effort in finding and posting that, but it still isn't relevant...
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Old 01-11-2017, 04:38 PM   #69
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It's relevant if you have no inkling of the Torsen design. Kind of a step 1 if you want to figure them out.

While the helical angles don't prevent backdrive, they increase the torque required to do so. Which, as you pointed out, was the basis behind the T1 design. Notice the helical angles on the sun gears are not mirrored in the T1. I thought this was just incorrect in this rendering, but no:



The T1 did not drive the sun gears (side gears, you call them?) together under torque. It seems, to me at least, the separation and axial forces on the helical gears were observed in the T1 and put to use in the T2.

Regardless, the video above does a very good job of demonstrating how the carrier transmits torque to the axles through the planet gears. At least it does with no sound... I don't have speakers so I don't know if there's narration.

There wasn't much effort. Came across it on an old Jalopnik post while "researching" at work.
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Old 01-11-2017, 04:51 PM   #70
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There is narration with the sound on, which discusses the worm wheel / backdrive at length. That's why I felt its important to point out that such a theory isn't true. I'd agree that as a piece of animation, it is nice, and that taking the video alone (no sound) would do a nice job at showing the inter-gear connection.

Excellent observation regarding the helix angles - while parallel-axis designs use a combination of right and left-hand helix gearing, making them thrust together or apart under load, Type-1 designs all use left-hand helix only gearing. The exception was for the Ford 9" Type-1 differentials, which are all RH. That means that both side gears thrust together, in the same direction (to the left as show in the photo posted, when drive torque is applied). The left side gear would be sandwiched between the right side gear and the casing, but both gears are pushing left. In coast mode (decel, reverse gear), they'd both thrust to the right instead.

All of that - including the symmetry observation - is relevant to parallel and crossed-axis models, since it does underscore how both use the same basic principles. Gears thrust under load and generate friction against the housing case. With a Type-1, they also add a bit of friction in the gear mesh itself, which does a lot of sliding across each other. That makes the overall "natural" friction level higher for crossed axis designs. But essentially, every thing I described previously still applies.
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Old 01-11-2017, 05:00 PM   #71
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Then there's the Lego "Torsen"... which actually does use high angle helical gears because that's all that's available.

Although, without opposing torques on the wheels this appears to be locked, not limited slip. More like a Detroit without the clicks.
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Old 01-13-2017, 01:51 PM   #72
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The Torsen is used in the Mustang road race cars, and is commonly used on rally cars. It is superior to the standard clutch style diff.

Now Torsens are non adjustable, but serious clutch based diffs can have a number of adjustments. So for certain types of racing (including drifting) that adjustment allows them to be better tailored to a specific track or condition. But if you aren't adjusting your preload or your power vs coast ramps twice a week (and doing maintenance 5 times as often), then the Torsen type is the way to go.
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