I've been looking around trying to figure out what sort of diff the soon-to-be-mine Miata has (I thought I heard a bit of wheelspin during U-turns when I test-drove it today), and I came across mention of T1 and T2 torsens, looked into it, discovered there was a third type (T3, how creative...), and was immensely confused by the evident 3-ways-to-do-the-same-thing. can anyone explain to me the difference between the three?
It's not really 'the same thing' that the variants are doing. The Torsen can be designed with as little as 2.5:1 torque bias for slippage, up to 6:1 bias and possibly higher if the friction surfaces are modified, by varying the helix angles of the sidegears and their mating gears. Torsens have a helix on the outside of the portion that an axle shaft goes into. As that angle is increased or decreased, the tendency to allow slippage is varied. So, it can be pretty aggressive, like with circle track cars with Winters QC axles. In that case you may have 500 or more horsepower, driving a car around a dirt track, which allows tire slippage against the surface. The tires WANT to spin anyway, and the high torque bias ensures that they do so, grabbing traction all the way. Then when the straight is reached, the bias releases and allows normal differentiation from side to side. As a practical matter, a Torsen-type diff can only transmit about 80% of the total torque available thru the gearset.
Whether or not an increasingly aggressive diff is chosen, depends on the intended audience for the vehicle. The miltary is going to want the maximum locking ability it can get (H-1 Hummers) with the best on road manners it can have. The Torsen is seamless in its transition from regular operation to wheelslip correction. A lot of drivers barely notice that the wheels have slipped and been caught by the diff. The best, bar none, for my money is the Detroit locker type, but it's awfully harsh and requires some driver education. Which is why you don't find it very often in OEM option books; where you'll find the Torsen and similar 'limited slip' diffs quite frequently. The hierarchy is: open diff, then friction plate ltd slip, then Torsen type, then gear type (Detroit).
The Torsen has GOT to be about the best ltd slip available. I'm a little surprised that it's not offered more.
Of course, I'm probably preaching to the choir here anyway, considering the universal anwer is 'Miata'.
Nice post Mikey, I learned something.
Your hierarchy statement ( The hierarchy is: open diff, then friction plate ltd slip, then Torsen type, then gear type (Detroit). ) should be tempered with your first sentence ( "depends on the intended audience for the vehicle").
I have a detroit locker in my hot rod truck (500+ hp). A friend, who spent his carreer setting up diffs for NASCAR, tried to tell me to stay away from the detroit locker for the street and I didn't listen. The truck is WAY scary in the dry and deadly anyother time. [1] Of course, power slides in the rain are a hoot IF you know its coming.
Other than drag racing, and perhaps LSR (Bonnevilee and paved mile events) the Torsen rules!
Again, thanks for the paragraph about helix angles.
David in Durango
[1] In a curve, the truck will "push" horribly on application of any power. Harsh is an understatement, IMO.
PS, the Mazda Torsen is wonderful!
Didn't we read about a hybrid torsen/clutch type being the best of both worlds? I thought the bummer about the torsen is that if you lift a wheel, it will act as an open diff, but with the hybrid clutch/torsen the clutches will keep some giddyup on the wheel with traction.
In reply to Teh E36 M3:
Dunno, never lifted a wheel in the Miata (guess I don't drive hard enough?)
anyone?
It's true.
I hate to spread anecdotal evidence, but some allege that if you lift a wheel on a torsen-equipped car under full throttle, then the wheel touches down hard enough to get good traction, you can bust the torsen.... dunno if its bs or not. I'd still like to get one- the worn out rx-7 clutch-type in the back of the midget doesn't lock up much, especially in tight corners. Can't justify the $1500 or so for that hybrid unit (giken?).
Every off-roader knows that dropping a spinning wheel on to the ground is a great way to bust stuff :) Torsens are tough, but high horsepower wheel hop will take 'em out. Usually a Miata will frag the transmission first.
The OS Geiken is expensive, but holy cow does it hook up. Feels like one of the Positractions we use in the V8 conversions. We're adding it to our catalog.
My statement about the Detroit Locker being harsh and requiring driver knowledge was based on my own experience. I had a '57 Chevy wagon converted to 4x4 with Jeep pickup parts, that when I bought it, had both differentials blown. The only gearset I could find 2 of in the yard I worked at, was 5.38:1, from Jeeps. The only complete Dana 44 center (for the rear) was a Detroit. Honest! The yard owner (my boss) let me have the Detroit for US$25. A sweet deal, to be sure, but I wanted a Spicer 4 pinion ltd slip. But I had only pieces/parts of any 4 pinion Spicers, no complete units, and I couldn't afford the US$125.00+ that would've been 'my' price thru work for a new one. So the Detroit, for better or worse.
The '57 had a 327/Muncie m-20/Jeep Dana 28 gear train, and with the short gears, I could get thru 3 of the 4 speeds in an intersection. Really cool for street racing, but about worthless for highway. Anything over 45 minutes at 60 mph was really tiresome.
The best/scariest story of that time was me coming out of a KFC parking lot on a snowy evening. My feet, wet from the snow, slipped off the clutch to the left and off the brake onto the throttle on the right, launching me rather dramatically, and since I was already turning left, the torque reaction pulled the throttle. 
So there I was: sideways in the street, throttle wide open, and heading west but body pointed southwest. It was a scary 5 or 6 seconds before I got it shut down. It seemed about like an hour. 
It was just good luck there was no oncoming traffic. The next morning at the shop, I found some better pedal covers off a rig in the yard 
, and vowed I would preach the gospel of staying away from Detroits unless you really, REALLY need them. They're a Godsend if you need them, but spooky at best if you don't. They can turn your world upside down in a heartbeat.
BTW, the Detroit True Track (TruTrak?) is basically a Torsen. Just for those who know Detroit stuff.
Keith wrote: BTW, the Detroit True Track (TruTrak?) is basically a Torsen. Just for those who know Detroit stuff.
Yup, but with a helix angle that's pretty mild. When it first came out, it was rated for about 250 hp; and not over 32 tires. Fine for front axle use as long as you didn't get real heavy with the right foot. A little shaky for rear and lots of power.
The newer versions of the Locker, are about the same as the older ones but with weaker springs and less radical ramps for the overrun operation. Not quite as spooky as the original, but still not to be taken lightly in a short wheelbase high horsepower car. Detroits like longer wheelbases, like over 140", really well. The longer WB calms down the reaction time and event harshness. But the LWB is contraindicated for auto-x, so that tells you where the Detroit and its newer offspring fit for little cars. The Detroit variants will probably be great for the tow rig, though.
For auto-x, the friction plate and Torsen variant ltd slips are PERFECT.
"
need one of these for my all trac
http://cgi.ebay.com/JDM-Toyota-ST185-Celica-Rear-Torsen-LSD-helical-ST205-/140449200891?pt=AU_Car_Parts_Accessories&hash=item20b36cbafb
all I know about torsens is that they require much less maintenance than clutch type lsd's
smog7 wrote: need one of these for my all trac http://cgi.ebay.com/JDM-Toyota-ST185-Celica-Rear-Torsen-LSD-helical-ST205-/140449200891?pt=AU_Car_Parts_Accessories&hash=item20b36cbafb all I know about torsens is that they require much less maintenance than clutch type lsd's
10-4! Basically keep the right fluid in, with the appropriate high pressure additives, and they'll live a GOOD long time! They are worth the money you'll pay, though I'm a little uncertain about the Giken hybrid.
You'll need to log in to post.
