Limited Slip Differentials

[Nick Graves]

AD08Rs hate being cold and have minimal tread - kudos that man!

At least it's a trad LSD - the Torsen one in the S2000 and 86 don't function if there is that big a difference in mu and it's fully open. With the engine at the wrong end, they're a bit hopeless.

The Leg End has a snow button that converts SH-AWD into boring AWD - just as well as its Yokos also dislike cold. You can imagine which one I choose to smoke around in...

[britlude]

at mot time when jacked up, and the man turns the back wheel, the other wheel has always turned the same way, regardless of speed... obviously this is with the turning input coming from a wheel, rather than the engine, so guessing i have a tight LSD then...

tho, in the recent snow and ice, i've had to knock mine out of drive (yes, auto, no, i don't care) in order for slow speed maneuverability as the LSD axle wants to push the car on in a straight line, regardless of steering lock....

in addition the TCS stops unexpected wheels spin by killing engine power. (i dont think it has the ability to talk to the abs and brake individual wheels accordingly, but i may be mistaken, mines is an early one, so maybe later ones got more sophisticated!)

[Kaz-kzukNA1]

Swipe or voice typing only for nearly a week and just started using the keyboard again after suffering from the side effect of flu and the covid autumn booster so missed the boat.

A-1.
91-94 standard coupe + 95 Type-R
Preloaded DF (Differential)

Regardless of the changes in the input torque, the locking torque is kept at constant figure.
There is a single spring washer at the back of the multiple wet friction discs and nothing else to increase the locking torque.

It's more of a stability improvement DF than a sport type.
Because of this, you will notice the lack/reduced traction with the sharp acceleration on the exit of tight slow turn on track.

Type-R is still the same preloaded type and using exactly the same spring washer but there are two of them instead to increase the initial locking torque.
Hence some 91-94 owners added the extra washer to their original DF.

95+ models
Preloaded + Torque reactive DF
From 95 onwards (except for NA1 Type-R), it still uses the spring washer to apply preload to the multiple wet friction discs but as you noted, the internal, planetary and the central gears are all now helical type.
When the engine torque applied to the DF, the central gear moves towards the multiple friction discs.
The more the engine torque, the harder the central gear presses against the friction discs.
Hence, propotinal locking torque against the input torque.

Still, not to the level of mechanical locking DF like the OS patented one but for all sorts of street driving conditions, OEM is good enough.


A-2.
Regarding driving on the snow….

From what you wrote, the DF was properly acted as the LSD.
I don't know how steep the hill was but without the LSD, you would end up with hard time climbing the compacted and already polished mirror like snow/ice surface.

Many ordinary production cars with Open type DF would simply get stranded on the snow not just because of the wrong tyre but also for the lack of LSD.
Once one of the drive wheel starts spinning freely without any traction, the other drive wheel won't even rotate because of the Open DF.

I used to live in Shibuya, Tokyo and there are so many hills/slopes even around the station area and just 2inches of snow was a nightmare for the drivers.
It rarely snow around that area and normally, it would melt away before settling.
So, almost no one changes the tyre for the winter.
Even if for a few inches of snow, many cars got stranded because of the tyres and the loss of drive on the hill without the LSD.

Sounds familiar here....


You at least managed to zigzag climb the hill so the LSD was working but the tyre was not suitable and the TCS killed the input torque.
Next time, switch off the TCS, adjust tyre pressure, use 2nd gear for the launch and if the condition permits, use reverse gear to reverse up the hill.

91-94 models are non-DBW and use TH cable.
The TCS is done using dedicated stepping motor and reduces the TH butterfly angle.
However, the control is almost like On and Off so in my personal view, it's actually dangerous.
I think I disabled it more than 20 years ago.

95+ models (except NA1 Type-R) are DBW and TCS is controlled by the same stepping motor at the TH body.
I don't know how good the TCS is on the DBW model but there is no sophisticated link between ECU/TCS/ABS/DF/etc so no active drivetrain algorithms on our NSX.


I used to take my NSX and other NSX on all sorts of snow conditions (fresh, powder, compressed, ice, sorbet, etc) using the summer, snow tyres and sometimes even with the use of tyre chain.
As long as the front nose can clear the block of snow that other larger cars or the HGV dropped on the road, NSX can perform fairly well on several different type of snowflakes.

Just needs to be extremely careful when crossing over the tyre tracks on the snow when being forced to change the lane.

Practicing on the low mu ground is good way of safely experiencing different type of driving environments.

The type of snowflakes makes significant effects on the performance of the snow tyres and something good in one area/country doesn't mean the same for the other.
Driving in the blizzard condition around Chicago while working in US, visiting Stuttgart every winter for several years, holidays in Canada, etc and the hire cars all had different makes/models of snow tyres.


With my generation in Japan, it was very popular to drive to the skiing resorts so I drove all sorts of cars with my friends every winter for years.
There are several areas that require the use of snow tyre by law before driving (just like some of the European countries) and recently the law got tightened and under specific condition, the driver is required to fit the tyre chain even on the snow tyres.
Otherwise, you'll be turned away.

Because more than 70% of the land in Japan is covered in mountain, the roads around these area are twisty and once the snowplow truck starts operating, they tend to become even narrower.
I would never drive on the snow without the LSD on the 2WD car.

Many delivery drivers in these snowy areas either use the van with the factory fitted LSD or modify it using the LSD from other models.


Hope I can drive my NSX soon as it was a big challenge moving any joints including the fingers as it just hurts so much.


Kaz

[duncan]

Thank you Kaz for those explanations, adding what others replied I think I’m getting a better understanding.

Limited Slip Diffs.
From your explanation for the 91-94 cars: they start locked and remain locked until stressed after which they slip. Presumably then they are not fully open but not fully locked either. That in my mind the other way around to my understanding of other LSDs.
For the 94 on cars: they start locked with I’m assuming a lower initial preload than the earlier cars to allow for parking/ low speed manoeuvring, however once stressed they stay locked.

Traction Control.
For 91- 94 cars: you regard TC as potentially dangerous and choose for yourself not to have it engaged.
In part the factory appears to have done the same and dispensed with TC, Nick (NZNick) notes his 99 type S was not fitted with TC. I’m assuming the factory fitted the earlier earlier / non Helical / type R crown wheel set to the type S cars.

For 95 on DBW cars: are you aware of others who would not choose to not to have TC enabled, in particular what is the view of Japanese owners?
For me I found the power cut to be the most disturbing aspect, if as you say the TC and ABS don’t talk to each other, the extent of power cut felt excessive and to be counter intuitive.

Having looked over TC related posts here and on Prime, it seems that those upgrading to S2000 ABS modulators have the TC deleted in the process anyway.

[britlude]

yup, the S2000 ABS doesn't make all 4 wheels sensor signals available on the output pins (some output 2) so the TCS cannot compare and contrast the wheels speeds to determine if TCS needs activating

i still have the TCS active as it helps when i'm out in snow!!!! now i have another car to commute in, so hopefully won't need to test it again!