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NA2 6MT differential to NSX-R spec question

11 July 2014
France, Switzerland
I am still refreshing my '98 engine and transmission. Engine is done, new fresh synchros are mounted (and new needle bearings where needed), diff case is open.
Wanted to tighten the differential to NSX-R spec so I bought these two parts:
(that's the J-spec NSX-R retainer, and a conical washer)

But here's the thing (lets take a diagram from Amayama for reference: https://www.amayama.com/en/catalogs.../chassis-and-transmission-7/differential-1346 )

NSX-R diff, seems almost identical to NA1:

and my diff (identical to 2002+ according to Amayama):

See how I have a conical spring washer (13 on bottom diagram) on one side, that's not present on the NSX-R.

Installing NSX-R parts would involve installing 11 & 15 (middle diagram) on the other side of the diff - and removing the needle bearing (9 15 & 8 on bottom diagram).

In the end that would mean:
- having two conical spring washers (one on each side)
- keeping the needle bearing on one side only (along with the existing conical washer)
- adding a snap ring and 60mm flat washer (14 & 9 on middle diagram) that are not there in my diff (the snap ring groove is there, it's just empty, means the casing is identical on all gens NSX)

Would that work at all ?
Is the existing conical washer redundant ?
Would the diff torque be OK ?


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The NSX-R differential is identical to the 91-94 differentials except for the preload spring configuration which is why its such a simple change for those years.

95-05 differentials had a slightly different internal design which shares a few parts but the clutch pack configuration is different as you noted, so trying to get the R diff parts to fit would be a shot in the dark. The 91-94 diff uses straight cut gears so the preload washers are solely responsible for the pressure in the clutch pack, whereas the 95+ differential uses helical cut gears which will vary the pressure on the clutch pack based on torque so messing with the preload washers could negatively affect the way the differential functions.

I'd probably either leave it alone if it's a street driven car or consider going with an aftermarket differential if you're tracking it hard.
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[MENTION=30520]Zoom[/MENTION] , it depends on what your definition of NSX-R diff is I suppose. To most people that just means increasing breakaway torque. Other than the slight differences [MENTION=33247]MotorMouth93[/MENTION] listed you can very easily increase the breakaway by changing just a single shim. The shim is part #5 on your diagram and is a 112 mm size. Part numbers 41261-PR8-000 to 41270-PR8-000 for the various sizes in 2 mm increments. Note it's actually EASIER than the 91-94 diffs to increase the breakaway as you don't need a press; you just unbolt the housing and it's sitting right on top.

You can see my 2005 differential refresh starting at post 142 and onwards in the following thread:


It's not a "1 size universal" here is an NSX-R shim that seems to apply to the 91-94 diffs. You need to know what your existing breakaway is. Then go up in shim thickness to target the NSX-R breakaway (I don't know that value but I'm sure someone does). The OEM maximum spec for a 6MT is 101 ft-lbs.


In the picture below the spring washer is on top (part #13 ), the single clutch is under it (can see the internal teeth, part #4 ) and then under that is the 112 mm breakaway torque shim part #5 that you can just see sitting in the teeth of the carrier (with the external teeth).

Good info for future searches :) Mine is going to get closed soon enough (trying to get replacement clutch discs so at least I wont come back to that..) so I wont get that shim in time, also my mechanics didnt have the proper tool to test the diff torque (need a specific wrench socket) so I wouldnt go and blindly change that... I suppose fresh clutch discs will make it feel as new which would be enough for me I hope.