About the Author: Michael Flood


  1. I never liked worm gears. Though they may be quieter, they have the highest coincidental wear and tear due to increased tooth friction when the teeth slide in the groves of another worm gear to force the other gear into motion.

    I am a certified mechanic/engineer. I have repaired many diffs and found that worm geared combination have more wear and tear than direct contact of planetary and other toothed gears that have slightly arched teeth for quietness. My father, an ex WW2 army mechanic, used to repair diffs of 1944-48 trucks and cars and had done so in modern diesel trucks until the 80's when I took over the business and he saw how little their diff gears had worn out after years of hard work since late WW2. Eaton diffs were the best as they are today. Chevrolet truck diffs were incredibly hard to destroy. International Harvested diffs, with years on fields and road use never saw a repairing service in our workshop bar a new diff oil changes. Their bearing were one of the best used in diffs in the USA.

  2. How does this guarantee perfect ratio in normal turns? The two blue gears always spin at the same speed, and they are both connected to to red and orange gears so doesn’t this mean the red and orange gears will spin at the same speed?Can someone help me pls?

  3. I wish it was like that in real life but it’s not. If 1 wheel has zero traction this type of diff will be useless.

  4. Whose mans is this, i dont get it if the worm spinning things are spinning attthesame speed then how can one wheel spin faster? Whaaaat

  5. Pretty sure I have torsens in my truck. Great for off roading. Let on the brakes and it locks the spinning wheels

  6. Watched this 5 times.. I'm still lost. How is it that during a turn, the wheels are "locked" but also have one wheel spin faster than the other?

  7. My Volvo is AWD, mainly through front but when it slips, rear is in use.. could i buy a torsen diff for the rear?

  8. Great video! Thanks for this excellent refresh on what people should know about their cars. I live in Canada because of our rugged weather, I sincerely think that all car should come with a limited slip differential either for front wheel drive or rear wheel drive cars. Open diff or traction control is for moderate weather and it is inadequate for what we have here. I think car companies should make the effort standardize limited slip differential on all models coming to Canada. Keep up the great work!

  9. No its BS that this axel will lock up if one wheel spins ..
    It will not but it will transfer more power to the other side at an instant.

  10. This explanation is abit misleading as if most of the differential explanation videos. The purpose of a differential is allow power "transfer" from higher to less resistance side. It utilizes the power transmission system. LSD and Torsen is quite different mechanism but serve the same purpose. LSD limits the power transfer at higher torque situation by locking up with the hub. Torsen limits power transfer at all time but at lower amount, depends on the angles between the spur-worm gears. The major pros of Torsen is almost maintenance free and being effective at lower torque. However, its always on characteristic causes under-steering. Hope it helps.

  11. through the video you deal like the power comes from one of the tyres and drives the differential so a w-gear drives a w-wheel firstly, which is wrong and the fact is the opposite, except no-engine-acceleration situation. power is usually driven through pinion to w-wheels to w-gears to tyers. so let's deal with facts.

  12. accelerating while taking a turn with a car is actually the same as accelerating in a one-tyre-slippery situation. both leads to a w-wheel tries to spin a w-gear which causes the pretended locking mechanism, if doing at all.

  13. please update the video to correct the low traction operation of a torsen differential. Torque applied is limited to the torque being applied to the tire spinning the fastest. In the case of near zero traction for one tire, the lack of torque resisting the spinning tire means that the other tire gets a proportionally reduced torque. Good for cornering, not so great for snow.

  14. The level of intelligence of engineers who come up with these technologies is staggering. While this is relatively easy to understand when it is explained, coming up with this technology initially is amazing.

  15. I didnt include gear ratio in the elecrical production prowess. If we employ gear boxes powered by low volt direct current motors the high speed side of gear box will propel a high output AC alternator.

  16. This system was invented and used by Walter Trucks in about 1930. Detroit True Trac and another brand called Wave Track use it too. Also Strange Engineering builds their own .

  17. Remeber those commercials like over the waves and the one from chevy on open diffs i think its called around the corner. Aim to explain it to a five year old, and dont include any jargin. If there is anything vaguely confusing, give the most straightforward answer possible. It would also be nice if you gave a simplified PHYSICAL REPRESENTATION YHAT WORKS, so that the simplified animation that barely explains anything isnt the only thing we can see. When you are learning about cars, visual learning with audio assistance is better than the opposite way around.

  18. This looks nothing like the 4 different Torsen differential housings I used to make. Also we called the central gear the sun gear and the smaller worm gears were called the planet gears. The planet gear bores ran parallel and concentric to the Sun gear. All the housings we made were for high HP applications (Boss Mustang, Raptor, Camaro & Stingray) so they all had 8 or 10 planetary gears.

  19. So if one tire is supplying torque through the axle shaft into the side of the diff like when you’re turning its open but if the engine is supplying the torque causing the wheel to spin it locks

  20. i have a 1996 jeep cherokee xj does the dana 35 rear end suppose to have thrust washers behind the spider gears or can i run it without them mine didnt have any when i pulled it out while replacing rear axle bearing and seals

  21. Read this and techdaemon's comment BEFORE watching the video. The Torsen does not work the way the video narrative suggests.

    1. The video begins a worm gear can turn the worm wheel, but the worm wheel cannot turn the worm gear. That statement is correct. What is not correct, is that the Torsen uses worm gears and worm wheels. Next he calls his worm wheel, a spur gear, which cannot mesh with a worm gear. Then, notice how the gears magically transform from worm gears to 90 degree helical gears when the animation assembles them into the differential case. 90 degree helical gears work much like the ring and pinion gears on cars and transmit power in both directions. Moreover, with worm gears and worm wheels, the worm gear is always the much smaller gear. This shows the opposite. Since the differential pinions (which he calls the worm wheel) is smaller in diameter to the axle side gear (which he calls the worm gear), it is actually easier for them to turn the axle side gear than the reverse. This invalidates the basis of his worm-gear-based premise. However, the narrative continues based on the false worm gear premise, even though it is obvious to all there are no worm gears and worm wheels, and thus the remainder of his explanation of how it works is also false. I will prove in the following that differential pinion gears driving the axle side gears is central to how the Torsen works in a low-traction environment.

    2. Gear types: Spur gears are the most efficient because all of the rotational thrust is applied between two gears in mesh is in their direction of rotation, which is 90 degrees to the shaft they spin on. Spur gears are never in contact with more than one tooth of the opposing gear at a time. The drawbacks are, since gears must have clearance to work, they generate noise and vibration when transferring from one tooth to the next. They are also not as strong because there is only one tooth in contact with the opposing gear. Helical gears are quieter and stronger because more than one tooth is engaged at all times as they slide in and out of contact, which is why they are used in transmissions. The downside of helix cut gears is gears sliding in and out of contact and the thrust vectors are not all in the direction of rotation of the gears, because the helix creates an inclined plane, thereby causing some thrust to be in line with the shaft, they rotate on. Optimizing this downside is what allows the Torsen bias its torque. One could argue that condition exists with 45 degree spur gears. That is true, but to a much smaller degree.

    3. Open Differential: With a standard open differential, the axle side gears and the differential pinion gear that spans the distance between the two axle side gears is a highly efficient 45 degree bevel spur gear. The only time the differential pinion would turn relative to the differential case is if the axles were not going the same speed, either due to a turn, or loss of traction on one of the wheels. Therefore, when traction is good, and the vehicle is traveling straight down the road, the differential pinion gears are not rotating relative to the differential carrier, and since the differential pinion gears are in mesh with the axle shafts side gears, the teeth of the differential pinion gears simply push on the axle side gears through their teeth, with no movement between the the gear teeth of the gears. With no gears moving relative to each other, the effect is as though the axles were simply splined to the differential carrier because the axles rotate at the same speed as the differential carrier. Assume the differential carrier is rotating at 2 rpm, and you go around a corner that reduces the inner wheel speed to 1 rpm, then the outer wheel speed must turn at 3 rpm. Next, assume we have 100 rpm and 100 lbf of torque applied to the differential carrier. 50 lbf torque would go to each wheel when there is adequate traction at both wheels. Assume we are stopped, we add power, and the right-side tire starts to spin at 10 lbf of torque but the left tire doesn't move. As the carrier continues to turn at 100 rpm, the torque to the right-side wheel drops to 10 lbf of torque because that is all that it can do. However, because the carrier is still rotating about the stationary left-side axle, the left-side axle drives differential pinion gear, which in turn drives the right-side axle gear, thereby doubling the rpm of the right-side axle. The force generated to turn the additional 100 rpm cannot exceed the 10 lbf maximum imposed by the right-side axle, but the opposing force that drives the right-side axle through the differential pinion is on the left-side axle side gear, so 10 lbf is exerted added to the total tractive force for a total of 20 lbf, 10 lbf to each wheel, even though only right-side axle is turning. An open diff has a 50/50 torque split, 100% of the time.

    4. Torsen Differential: While going straight down the road and axles turning the same speed, the Torsen differential behaves similarly to the open differential. If you simply go around a corner, and one wheel is going proportionately faster than the other, there is no torque being applied through the turning differential pinions because their axle side gears and rotating differential carrier are both perfectly coordinated. If the left-side wheel is on dry pavement, and the right-side wheel is off the ground, the differential carrier revolves around the left-side fixed axle side gear, and as with the open differential, transfers the left-side rpm through the differential pinions to the right-side axle side gear. Because the wheel is off the ground, very little additional torque against the left-side axle side gear is required to transfer the rpm from the left-side axle to the right-side, and thus negligible torque on the left-side axle gear is available to move the vehicle. If the right-hand wheel is on ice, and it can generate 10 lbf of torque, the differential carrier again revolves around the left-side fixed axle side gear, but this time it requires significantly more than 10 lbf of torque is required due to the thrust vectors of the helical gears to transfer the the rpm through the differential pinions to the right-side axle side gear, and arrive with 10 lbf of torque. The extra effort of torque as a ratio required at the left-side axle side gear is the design Torque Bias Ratio (TBR). If the designed TBR can achieve 3:1, then there will be can be up to 30 lbf applied to the left-side axle side gear, 10 lbf to the right-side axle side gear for a total of 40 lbf. If 40 lbf, is not sufficient to move the vehicle, the left wheel will remain stationary, and the right wheel will continue spinning at twice the differential carrier rpm, just like with an open differential. If there were a worm gear and worm wheel used here, it would be instant lockup, and there could be no TBR.

    5. Torsen Implications:
    – When turning a corner, it is not effectively different than an open differential.
    – When the differential carrier rpm is not perfectly coordinated between the axles, as is the case when there is a traction problem, it biases torque to the wheel with the lowest rpm.
    – If there is 0 lbf required to turn one wheel, there is 3 x 0 = 0 lbf transferred to the stationary wheel.
    – If there is 10 lbf force on the spinning wheel, with a TBR of 3:1, there is a maximum of tractive force of 40 lbf available. If that is not enough to move the vehicle, it will still behave like an open differential with one wheels spinning
    – If 40 lbf was not available to move the vehicle, you could drag the brakes. By adding 10 lbf to both wheels, you would increase the tractive lbf at the stationary wheels to. (10) + (30 + 30 – 10 = 50) = 60 lbf of total tractive force. Of course with one wheel off the ground being at 0 lbf for one wheel, you could also get moving by applying the brakes and gas.
    – If I can drag the brakes on a Torsen and gain more traction, then why doesn't that work with an open differential with its 45 degree spur gears? It does to a lesser degree. Computers and traction control these days can also apply the brakes to the spinning wheel to bias torque perfectly to meet conditions.

     Again, techdaemon's comment explains accurately how this device functions, which is critical to its application and usage.

  22. Good old worm, spur and ring gears, no tatoos, no alt lifestyles, sin drogas, it was a better time. Input and output shafts, i miss them

  23. I didn't understand; if the spur gears are always locked to each other, how can each wheel rotate in different speeds when negotiating a curve? When telling the torsen diff supports different speeds in each wheel, the graphics show like there are no spur gears. But they are always there and locked all the time. I have to see this bu myself in real life. I know the conventional diff, it's really easy to understand, but this video messed my mind up!

  24. Great video. You explained it so well, even an idiot like me got it. I have felt it before in my RX-8, torsen is awesome. Especially when you`r into shaking car asses.

  25. so with this thing car wheels will never stop rotation on one side right??? not like old diff will let one side wheels stop rotating…

  26. That was actually a great video understand Thank you I just purchased a torque lock diff and 4.11 gears for my ss

  27. Is there a Toy model of this Torsen Differential available anywhere on internet so I can buy?

  28. A great system for road car applications as it is not intrusive to the electronic setup of the car.
    As used on the Ford focus RS !!!!
    Small differential oil coolers have been used to keep the oil from overheating and breaking down.
    As they say horses for courses.

  29. as brilliant as this design is, i wish the nomenclature was correct.
    a spur gear has straight teeth. these are helical gears. except the spur gears on the end of the worms.
    a worm gear ( or crossed helix) will drive either way unless the pitch of worm falls below 25° or so…
    i hate bevel gears😉

  30. The worm wheel rubs against the other worm wheel with a bunch of schleem.
    It’s important that the worm wheels rub together because the worms have all the fleeb juice.
    The blamphs rub against the trumbles.
    And that leaves you with a regular old Torsen differential.

  31. JTEKT may hold the patent on this , but they didn't invent it . The Gleason Torque Sending Differential came out over 50 years ago.

  32. 2 things about this explanation:
    1. There has to be some amount of grip on the wheel with lesser traction to cause the mechanism to start to lock up and send power to the other side. This is never stated in the video and also seems to be lost on people when trying to explain most differentials. This diff works off of a torque bias ratio so lets say that ratio is 4:1. That means that in a situation where 1 wheel has less grip than the other, the diff can send 4 times the amount of torque to the outside wheel to compensate. Its nice because then you don't spin all the power away on the inside wheel. However the problem with this is that lets say the wheel with lesser grip actually has no grip and is putting 0 lb-ft of torque to the ground. Well 4*0 = 0 so therefore, the wheel with lesser grip spins and no torque gets transferred to the other wheel. That thing about full lockup with a wheel on ice is incorrect. Also when it does that its still not the most efficient thing you can have because the its now just working to couple the wheels together and send some amount of power to each instead of to each proportional to how much traction each actually has. The video is misleading however because if one wheel completely looses traction, it will not be able to lock. The worm wheel on the side that has no traction will just spin the wheel on the side that does right around the worm gear but it won't actually transfer any torque to the wheel. The graphic shows the wheel in water or on ice which would imply that it would have no traction at all. In that case, the lock up will not happen as shown because of how the torque bias ratio works as mentioned above. The key thing to remember that while a worm wheel cannot spin a a worm gear as stated, the worm wheel can spin on its axis around the worm gear while the worm gear is stationary and if it is doing so, it isn't transferring the torque to that wheel.

    2. It is not the most unique and ingenious method for providing differential action and overcoming the traction difference problem. It still has a fatal flaw which is that it never fully gets rid of 1 wheel slip. The most unique and ingenious diff is the Weismann differential. This is the only one that fully gets rid of one wheel slip – that fatal flaw. In short, the Weismann sends power to each wheel proportional to how much grip each wheel has. So if one wheel has 3 times the grip as the other, it'll get 3 times the power, if its got 4 times the grip, it'll get 4 times the power and so on. Critically, what the Weismann will do that all others won't, is if that one wheel is on ice or in the air lets say, it will send 100% of power to the wheel that's on the ground with the grip and 0% of power to the wheel in the air or with no grip. That's what makes it the best and most ingenious design.

    So this video does a good job with the animations for the most part but does a shit job with the explanation. Leaves a few critical things out and gets a couple of things completely wrong.

  33. I'm thinking kinetically viscous coupling would be more advantageous. Instead of applying the viscous coupling directly between the two halves of the drive shaft, though, use planetary gearing to multiply the velocities and apply viscous coupling to the much more rapidly spinning plates. While this adds some additional complexity and weight, it might reduce overall weight. Then again, perhaps not!

    An alternative approach would involve a turbulent flow surface plates whereby either plate could easily drive the other through a high weight gear oil using principles similar to Tesla's Pneumatic Valve: https://en.wikipedia.org/wiki/Tesla_valve

  34. Still not an accurate view of Vern Gleasman's differential, but pretty nice graphics. In actual use the Torsen beats clutch types by 1. acting instantly with seamless transition between differential action and traction adding action, and 2. never wearing out. No, it's not a "locker" so it will not replace a spool for all-out drag racing or all-or-nothing lockers for 4×4 applications. But for daily drivers in all weather applications it's hard to beat. Add in the action of most traction control systems and selective brake application will increase the torque bias beyond what the Torsen supplies by itself.

    One thing I dislike about the Torsen is that it does its job too well. It's often hard to get the rear end to break free and skate around freely for long before the torque sensing mechanism finds grip and replants the rear wheels. I'd like to try the T2R that has a preload that might allow this. A clutch type is great for this, and doing smoky burnouts, but is a terror in the rain and wears out. Any type that forces the halfshafts together by force dumbly is great for straight-line dry pavement, but makes turning on slippery pavement a scary endeavor.

  35. 2:42 Better redraw that because both are rotating in the same direction.

    If the right hand side were turning the opposite direction you'd make quite the turn.

  36. Originally made for military aircraft tow/tractors. The first manufacturer was Gleason gear works hence they were called Gleason Torsten differentials. Back in the 80’s I got some prototypes made for the Toyota mini truck 4X4. I replaced the front & rear “True Trac” that I had previously installed (really couldn’t tell they worked then they grenaded) with these Torsen’s. They worked like a dream. Unlike most posi’s and lockers, I had great steering control on snow and ice yet great traction. Unfortunately the production models were made with gears that were hardened “powdered metal” not billet like my prototype. I’m sure that short cut method was short lived because they scattered even with the puny little 22R motor. They now have an excellent endurance that many foreign and domestic manufacturers use these in their high performance vehicles now and they are perhaps as good as any electronic traction control. They had different torque bias ratios. I don’t know what mine was but it was perfect. In a two 2wd test, I did see one dive wheel in the air and the truck did pull forward up an incline without wild wheel spin. The free wheel turned about the same as the one on the ground. It seems that an outside force like running faster around a turn can override the lesser wheel.

Leave a Reply

Your email address will not be published. Required fields are marked *