Eunos versus Aussie MX5 Diffs

aussiecossie · Postby **aussiecossie** » Sun May 21, 2023 8:24 am

Morning all,

From personal experience I know that NA6 diffs are not that strong but my questions relate to JDM Eunos cars - firstly, did they all have LSD's (?or was that torque sensing) and secondly, if they did, are they stronger than standard NA6 diffs?

Cheers

Jeo · Postby **Jeo** » Sun May 21, 2023 11:36 am

Not all imports had an LSD. If they did though it was viscous, not torsen.

It's generally the ring gear that fails in the 6" diffs so LSD or not doesn't make a lot of difference.

aussiecossie · Postby **aussiecossie** » Sun May 21, 2023 12:49 pm

Thanks Jeo, so am I right in understanding that an NA6 diff, whether open or LSD, will always be weaker than an NA8 one?

greenMachine · Postby **greenMachine** » Sun May 21, 2023 12:55 pm

Yes, that is my understanding.

Note also that the viscous LSD is subject to deterioration of the fluid's ability to perform its function and it tends to move towards an 'open' state often described as the fluid 'wearing out', whereas the Torsens are pretty bulletproof.

:mrgreen:

bruce · Postby **bruce** » Sun May 21, 2023 2:22 pm

Bear in mind the diffs are around 30 years old and would be a bit worn. My Torsen is noisy (a hard life with previous owners).

StillIC · Postby **StillIC** » Mon May 22, 2023 9:15 am

My JDM NA6 does have a Viscous LSD; I believe it was an option.

Many have said the NA6 viscous diffs are crap; they wear out and will break. Mine has 180 Mm (mega metres) on it and it works great. I can feel it chirp the inside wheel when cornering into some driveways. It pulls hard out of tight corners on the race track. Sometimes driving straight on grass/mud one wheel will slip slightly and there is a slight hesitation in forward progress, but the other wheel picks up the drive within a small fraction of a second and progress continues. And there is zero pulling, locking/unlocking, or adverse feeling from it whatsoever. It is just smooth in, smooth out of corners.

I like it. I think it is a shame that the larger NA8 diff was not offered with a viscous LSD.

greenMachine · Postby **greenMachine** » Mon May 22, 2023 2:29 pm

I presume you have changed the diff fluid?

I remember reading, I think on Mt.net(!), of someone reporting their good experience with these viscous diffs and a regular schedule of fluid changes was part of the reason for their happiness with it. IIRC there was a little more to it but nothing very dramatic.

I assume this was in a later 7in diff, because a power bump was involved - but I don't know if this was so, or even if retro-fitting one to the later bigger diffs is even possible.

:mrgreen:

StillIC · Postby **StillIC** » Mon May 22, 2023 3:42 pm

GM, the viscous fluid can't be changed AFAIK. It is held in a sealed unit in the diff centre. It doesn't mix with the gear oil in the diff.

greenMachine · Postby **greenMachine** » Mon May 22, 2023 7:35 pm

Yes, you are right, but it is possible, at least according to my memory of this thread/post. It is certainly nothing like undoing a drain and filler plugs as per a normal open or any other form of LSD that I know of. It may be the unit had to be sent somewhere, I can't remember the details but the poster was doing quite a sales job on the viscous units and replacement of the fluid was part of his pitch. Could have all been BS too (it is the internet :roll:

), but I don't remember there being any serious pile on like Mt.net is known for.

I see that you have 180K kms, that is pretty good life for it to be still performing well. Yes, like anything else the Torsens wear, and I have heard of a broken spring in the mechanism I think. They also have their limitations, mainly around need to keep the rear wheels on the ground because it will 'go open' if one loses contact with the ground.

:mrgreen:

StillIC · Postby **StillIC** » Fri Jun 02, 2023 5:13 pm

StillIC wrote:.....
I like it. I think it is a shame that the larger NA8 diff was not offered with a viscous LSD.

Perhaps I am wrong about this?! Here is an image of an RX7 VLSD, albeit broken. Is this the same centre as the 7 inch MX5 diff? Is it actually a VLSD??

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/can-you-break-viscous-type-lsd-861280/#&gid=1&pid=1

Ross · Postby **Ross** » Tue Jun 06, 2023 2:09 pm

I've got a VLSD in my 91 Eunos V-Special Roadster :lol:

OK, my MX-5

My experience is exactly the same as StillIC's and it seems to work as intended - If i've stopped on the side of the road somewhere, left wheel on gravel and right wheel on bitumen, and decided to depart rapidly, it does so, slight wheel spin from the LHS but the forward progress is much better than an open diff. My daughters ADM MX-5 has an open diff, I have dríven both.

On the rebuild option, if they are anything like the VLSD in the centre diff of a Range Rover, they are not really "servicable".
My FIL pulled his from his 95 RR and took it to a machinist to have it split, we then removed the "fluid" which had actually turned to rubber and wasn't providing any slip. We then refilled with a silicon fluid and had it re-welded to seal it.
Worked fine after that.
Rebuildable - yes, if you know what you are doing, have the right equipement and materials.
Seviceable - No.

StillIC · Postby **StillIC** » Tue Jun 06, 2023 4:10 pm

Ross wrote:...
Rebuildable - yes, if you know what you are doing, have the right equipement and materials.
Seviceable - No.

On GM's thought that the fluid might be replaceable with some work, I went Googling. I didn't find much, but two things caught my interest:
1) a cutaway drawing of the MX5 VLSD showed the fluid sealed by tubes with balls punched into them. Might be possible to drill them out?
2) the fluid in VLSDs is sensitive to temperature, and apparently works better (less slip) with some heat in the fluid.