LSD Limited slip diff differential

[madras]

Hi, does anyone know where to get a diff rebuilt. I think after 135k miles mine is not locking up as much and also letting one wheel spin a bit more than it should if that's possible with this type of diff.

Gear oil was changed 18months ago so not quite due yet.

Many thanks,
Chris

[goldnsx]

Before you spend money did you check the torque according to the manual?

[madras]

No, how would I do that? I did ask Honda to check it about a year ago and they just said it was fine.

[duncan]

Jack the car up, put it in gear and turn the wheel over with a torque wrench, see attached PDF. Or ask garage to do and report on the torque obtained.

[madras]

Thanks. And whats the fix? a new diff or can they be rebuilt - do the parts come from Honda or is that just a complete diff?

[Kaz-kzukNA1]

Hi, Chris.

If you have original/earlier DF design on your NSX, I’m afraid the initial locking torque is not that high any way so it will let the inside wheel to spin if driven hard through the corner.
The design was aimed at more towards the straight line/side wind stability at high speed driving than the traction at the corner exit.


Not sure which type of DF you have on your NSX but you need to be aware of two different methods for testing the locking torque.

The procedure in the above pdf file is for the later spec DF that uses the helical gears at the internal/planetary/central gears with input torque reactive type. Hence, the test requires the trans to be in 1st gear.


The original DF design is just a preload type with non-helical gears used so the test procedure is similar but you need to keep the trans in neutral.
Lift up just the right rear wheel while keeping other three wheels on the ground and block them to prevent any movements.
Due to the way the DF is engaged, you must check the locking torque only at the right rear wheel.
The detail of the procedure and spec is in the original workshop manual released in 1990.


There are multiple clutch discs submerged in MTF inside the DF and you can refurbish your original DF by replacing these discs to the new ones.
These discs and plates are available through Honda.

If you have the earlier DF design, you can increase the initial locking torque by replacing/adding the spring plate from Type-R model although it may not be enough depending on the shape of the race track.

If you use your NSX hard on track, although it is mega-expensive, you may want to consider going for the aftermarket DF such as the one from OS Giken (but not the off-the-shelf model, you want the one customised for NSX) balancing between the behaviour/noise on street driving and track usage.

In any cases, it will require SST for DF service work and although the SST are not that expensive, not sure whether they are still available or not. Also, if you have 5MT Gbox, putting back the trans case over the main/counter/reverse shafts requires almost like three hands so may want to take it to Honda.

Kaz

[madras]

Thanks Kaz. I use Honda for the servicing, it's a early 5 speed originally with the longer gears but now with the later 1995 shorter gears. Could be that it is ok, but certainly spinning up way too much compared to other cars I've driven hard on track - what is the locking slip %? I have an e36m3 evo and that is 25% and this seems a world away from that. It also seems to spin the left hand rear more than the right hand consistently in a straight line when I tested it on wet roads - could the diff do that do you know?

[Kaz-kzukNA1]

Hi, Chris.

If you are using the Gbox from the later model, then you may already have the torque reactive preloaded later spec LSD unless you have swapped out the gears on the main/counter shafts and left the DF untouched from your original Gbox.

In Japan, the upgraded LSD was released from NA1-130 type in 1995 with Gbox serial no. starting at SR8M-6100001 onwards.
AT model stayed with the simple preloaded spec.

I’m not good at in using the ‘year model’ because the definition is different from one country to another but I think UK NSX was equipped with the same upgraded LSD from similar time frame.

In fact, looking at the parts system, if you have SR8M-61* series Gbox, you have the later spec LSD.


I’m more familiar with the electrically controlled DF which can have several maps so not sure what the best way to explain the locking ratio on this type of DF.

Preload won’t change regardless of differential torque input and this characteristic is the same for both the early/later spec LSD on our NSX.

Torque reactive will kick in once the differential input exceeds the preload and the angle of helical gear will determine the thrust force against the multiple clutch plates which generates the locking torque.
Can’t remember the torque bias ratio/slope but I think it was around 1.5 – 1.8.

If you have the later spec LSD, you should follow the test procedure described in the above pdf file.


Kaz