Weird looking diff
08-13-2009, 09:30 AM
#1
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Weird looking diff
Anyone know what this is? It came out of the 03. I've never seen one with a spring in it before.
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Last edited by levnubhin; 03-12-2010 at 03:50 PM.
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08-13-2009, 09:41 AM
#4
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It looks like an open, is it not? What's it worth?
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08-13-2009, 09:46 AM
#5
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The '03 Miata has a Tochigi Fuji Super LSD (tm). It is a spring preloaded, cone clutch, torque sensing differential. In this differential, the normal separation forces created by the spider gears drives the side gears apart. Instead of being entirely constrained by bearings, this force, proportional to the torque transmitted, pushes a cone clutch on each side together. It, like the Torsens installed in Miatas before it, has relatively modest torque bias ratio. I think the TBR is 2.0 to 1 whereas even the Torsen could manage 2.5 to 1. There is a minor spring preload on the Tochigi which the Torsen Type I and II do not have.
Torque Bias Ratio is the ratio of the maximum split of torque between the axle shafts. The TBR of the Miata Torsen is about 2.5 to 1. This is independent of the amount of torque and axle speed. If one wheel is supporting 50 ft-lbs, the other can support up to 125 ft-lbs (2.5 x 50 = 125). If that 50 ft-lb wheel, sitting on gravel, hits a patch of ice and drops to 5 ft-lbs, the other wheel will also drop to 12.5 ft-lbs max (2.5 x 5 = 12.5). If 12.5 ft-lbs of torque on the high traction wheel is not enough to move the car, the Torsen will allow the ice wheel to spin up just like an open differential.
A regular open differential has a TBR of 1 to 1 (actually about 1.1 to 1 due to internal friction). If one wheel is supporting 50 ft-lbs, the other can support no more than 50 ft-lbs. This is why it is easy for the ice wheel to spin up on an open diff. 5 ft-lbs on the ice wheel means only 5 ft-lbs on the traction wheel. Of course, 5 ft-lbs won't move anything, so the low traction wheel spins up.
The Tochigi Fuji preload is only good for 36 ft-lbs. A Torsen II will always divide at 2.5 to 1. So, if the low traction wheel will support 1 ft-lb, a Tochigi Fuji will provide 37 ft-lbs to the other wheel and a Type II will only send 2.5 ft-lbs to the other wheel.
As you can see the Fuji diff is the mildest of the OEM ones available, having a TBR closest to an open diff. Having recently switched from a TorSen II to a Tochigi Fuji I would definitely agree with this and have noticed a marked reduction in tyre chirping pulling out of T junctions and parking spaces.
Torque Bias Ratio is the ratio of the maximum split of torque between the axle shafts. The TBR of the Miata Torsen is about 2.5 to 1. This is independent of the amount of torque and axle speed. If one wheel is supporting 50 ft-lbs, the other can support up to 125 ft-lbs (2.5 x 50 = 125). If that 50 ft-lb wheel, sitting on gravel, hits a patch of ice and drops to 5 ft-lbs, the other wheel will also drop to 12.5 ft-lbs max (2.5 x 5 = 12.5). If 12.5 ft-lbs of torque on the high traction wheel is not enough to move the car, the Torsen will allow the ice wheel to spin up just like an open differential.
A regular open differential has a TBR of 1 to 1 (actually about 1.1 to 1 due to internal friction). If one wheel is supporting 50 ft-lbs, the other can support no more than 50 ft-lbs. This is why it is easy for the ice wheel to spin up on an open diff. 5 ft-lbs on the ice wheel means only 5 ft-lbs on the traction wheel. Of course, 5 ft-lbs won't move anything, so the low traction wheel spins up.
The Tochigi Fuji preload is only good for 36 ft-lbs. A Torsen II will always divide at 2.5 to 1. So, if the low traction wheel will support 1 ft-lb, a Tochigi Fuji will provide 37 ft-lbs to the other wheel and a Type II will only send 2.5 ft-lbs to the other wheel.
As you can see the Fuji diff is the mildest of the OEM ones available, having a TBR closest to an open diff. Having recently switched from a TorSen II to a Tochigi Fuji I would definitely agree with this and have noticed a marked reduction in tyre chirping pulling out of T junctions and parking spaces.
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10-07-2009, 01:02 PM
#6
As you can see the Fuji diff is the mildest of the OEM ones available, having a TBR closest to an open diff. Having recently switched from a TorSen II to a Tochigi Fuji I would definitely agree with this and have noticed a marked reduction in tyre chirping pulling out of T junctions and parking spaces.
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10-07-2009, 01:28 PM
#10
I was pretty sure he switched to another TorSen...but knew it was recent which made the lack of quoting peak my interest.
I've seen all the m.net threads on the cone clutches shedding their tabs...and want to make sure this will hold up for a few years of my 150 mile daily commute before I commit to the install.
I've seen all the m.net threads on the cone clutches shedding their tabs...and want to make sure this will hold up for a few years of my 150 mile daily commute before I commit to the install.
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10-07-2009, 02:09 PM
#13
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Having recently switched from a TorSen II to a Tochigi Fuji I would definitely agree with this and have noticed a marked reduction in tyre chirping pulling out of T junctions and parking spaces.
Interested because my track car is getting a Torsen II for xmas...
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10-07-2009, 02:29 PM
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On a different note: my Torsen II is from a 2002 or something and used single piece shafts according to the docs.
My 94 has two piece shafts with stubs. I read that the single piece halfshaft uses different machined groves to oil the seal than the stub shaft design
But it will just fit?
My 94 has two piece shafts with stubs. I read that the single piece halfshaft uses different machined groves to oil the seal than the stub shaft design
But it will just fit?
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