I wish this was added as a disclaimer to every forum post recommending GM Synchromesh. I wonder if the wiki could be updated with this info under fluids section?
I would like to hear from Larry specifically why he doesn't like it. IIRC, there has only been one '91-'94 clutch-type LSD that has been rebuilt that used GM Synchromesh. When you consider the number of NSX owners putting this MTF in their clutch-type LSDs over all these years, that's not a statistically high failure rate.
The problem with transaxles that share MTF with clutch-type LSDs is that it is hard to balance lubricants to make synchros AND clutch LSDs happy. Anti-wear additives, extreme pressure additives, and friction modifiers all need to be balanced. Not easy, and is probably one of the reasons why Honda abandoned clutch LSDs later:
https://bobistheoilguy.com/forums/ubbthreads.php/topics/729344/EP_Additives_-_Lubricant_Rheol#Post729344
There aren't many automotive manufacturers that have transaxles with clutch-type LSDs (the NSX Torque Reactive Differential referred to above). But, data does exist out there for other Honda's... Civics, Integras, etc. with aftermarket clutch LSDs (Spoon, Mugen, Kaaz, OBX, Cusco, etc). Sometimes it's hard to read through Honda-Tech, but you'll find all kinds of information on various MTFs and homebrew cocktails people have used on the street and track over the past ten years.
If you read through it, you'll notice a trend that Honda MTF works great on the street, but does not hold up on the track once a certain temperature is reached. The oil/friction modifiers break down and you need to replace it early.
Racers predominantly use Kaaz MTF (which doesn't appear to be synchro-friendly in cold weather... i.e. not great as a daily-driver), Torco, Motul, or GM synchromesh with friction modifier as necessary.
As racers and other street users have used GM Synchromesh on their Honda clutch-type LSDs for many years under extreme conditions without complaints, then it should obviously work great for our '91-'94 NSX transmissions with similar design/materials used (synchros, yellow metals, oil passageways, tolerances, etc).
As I said before, I've used the 2qt GM Synchromesh blend with 1qt friction modified, and it worked great for 40k miles. Break-away torque was about 85ft-lbs and near the high-side of the SM spec. I've since put another 30k miles on this transmission using Amsoil and Honda white cap. About 130k total on my '92 tranny. The transmission is currently out to replace my SOS twin carbon clutch and I will preventatively replace my ISB's at this time. GM Synchromesh is going back in. :smile:
If the car was under warranty, I would use the Honda MTF and replace it more frequently. That's what I have to do with my '14 MDX because Honda ATF sucks too. However, at this point, I'll take my chances with the nice, smooth gear changes GM Synchromesh allows over Honda MTF. My diff and synchros work fine so far after 60k miles of it (like all the people over on Honda-Tech with clutch-type LSDs and our synchros)... but of course, YMMV.
