Limited Slip Differentials

[duncan]

My understanding is that the Limited Slip Differential changed on manual transmission cars in 1995.
It went from a Torque Control Differential to a Torque Reactive Differential.

So as Question 1, how do each of the set ups work?

Both comprise a set of wet stacked clutch plates that can lock together to lock the axles:
- the 1991-1994 cars have a straight tooth inner gear in the differential whilst,
- the 1995+ have a helical inner gear

Help me here but I’m assuming
- with the earlier & auto cars one axle spins up, the clutch plates heat up with the spinning until they expand and then lock up, if both axles rotate at the same speed their is no lock up.
- on the later manuals, the helical nature of the gear induces an axial loading and this pulls the plates together thus locking the pack, again if both axles rotate at the same speed their is no lock up. In addition, on over-run or slipping backwards (see below) the diff unlocks.


And as Question 2, and I appreciate that their may be a clue from the Limited in LSD, but, in either case can the axle be induced or tricked into locking?


I ask because when trying to drive my car (manual, 1995) in Sunday night’s snow I had great difficultly in getting and maintaining traction. Trying to move off on hills; low revs, trickle away and I stalled, more revs and I was spinning without traction, if I caught traction the car had a really heavy, dead throttle response (no increase in RPM with significant throttle depression but slowing and stalling without) and when moving I was getting some form of cycling / pulsing from the drive train.
No doubt those behind on the hill watching me saw tooth at 45 degrees across two lanes were amused but I wasn’t.
Admittedly the Advan AD08 tyres may have been sub-optimal for the situation.

[NSX 2000]

This may or may not answer either of your questions.
Do you have a TCS button near the instrument cluster? I know I do, and this may (I'm guessing) activate how much spinning one wheel is allowed to do before they both turn (spin). I know in some cases car manuals tell you turn TCS off when driving in snow or mud so that both wheels turn (spin) at the same time.

[duncan]

That’s a thought, pity I didn’t think of it at the time - but - I won’t go out to try it now.
I’ll have a read up.
Thanks.

[britlude]

if I caught traction the car had a really heavy, dead throttle response

sounds like TCS kicking in... it should be accompanied by a flashing TCS lamp on the dash, (in the rev counter i think)...

giving it more beans won't make any difference it'll still try to kill the engine power, it only 'ticks off' if you momentarily lift off the throttle and reapply....

(found this out when an abs sensor failed, i was turning tight out of a garage forecourt , the TCS was convinced the rear wheels were spinning and killed the power... as i was trying to pull away up a hill!... pretty awkward to lift off completely and re apply with someone close behind that accelerated better than me!)

[duncan]

I’ve had a read, page 146 and 147 of the handbook: there it notes
- that the TCS will brake a spinning wheel and will also reduce engine power. (I certain felt the reduced power, i.e the car would barely go uphill)
- that it can be switched off but only suggests that when the folding spare is used. (Logical as the spare is a different diameter to both the front and rear wheels)
I can’t see any suggestion for disabling it’s use in mud or snow. (Though I used to do that very thing with my AWD Audi TT and had forgotten)

SO THANKS Paul and Jonathan, yes, I should have tried switching the traction off: thinking it through, with one wheel spinning it should then provoke the LSD into locking, I’m not about to go out and try,
ANYWAY, as lesson learned, even after 18 years ownership, read the b****y instruction.

Any thoughts from anyone else?

[NZNick]

My car doesn’t have TCS, so I don’t know what I’m missing. Also, not had need to use the car in snow so far, so nothing to add, sorry.
Kaz has driven his car in snow previously, shod with AD08’s - braver man than me!

[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!