Miata Stock Transmissions - Fluid Recommendations
 

Hey All - thought I would start a thread to find out what everyone is running in their transmissions for race/track days. I'm currently using Valvoline SynPower 75W-90 Full Synthetic Gear Oil and have started to notice 3rd and 5th getting pretty grindy on aggressive shifts. Back in my honda days in the early 2000s this was solved by GM Synchromesh Friction Modified, but I'm not sure if that's the right cure all when considering the heat/wear of track day or race usage.

I'm currently running the Motorcraft unicorn tears stuff that everyone seems to love. I've though about switching it out for something else due to some crunching when cold, but that could be due to my 5 speed being old and worn out. I mostly autocross but have had it in the car for a few years including a track day. No real issues with it.

Ford Motorcraft XT-M5-QS 75-90 gear oil is the actual name.

I have Redline 75w-90 in mine and it's not good. Super crunchy going into gear when warm - can't shift it quickly at all. Going to try the motorcraft stuff next.

I ran the Ford Motorcraft XT-M5 in my 5 speed just like SimBa. It eliminated the 2nd-3rd gear grind that the car originally had when I got it. Never had any issues running ~200whp on track with it. More recently, when I dropped my 5 speed back in temporarily, I switched to a 50/50 mix of Redline MT90/Lightweight Shockproof. It seemed to like that even more. Smoother shifts when cold, for whatever reason. Plus the fluid turned that sweet baby blue color from the Shockproof. That's gotta be helping something.

I've also heard the MT90/Lightweight Shockproof combo is good. I know Bofi racing recommends it. I plan to try that next time I'm swapping the fluids.

Am I missing something? Thought the Redline 75w-90 was a GL5 gear oil for use in differentials, not manual transmissions.

Yeah, I had good luck with it. My original 6 speed was filled with it when I picked it up from the PO and he said the fluid made it notchier but he liked it for track use. Come to find out, that trans was rebuilt missing a shift fork bushing. Swapping to that fluid in my 5 speed made it a little less notchy.

While we're at it: I also have run Motorcraft dual clutch fluid in a pinch (for way longer than I originally intended) in both my 5 and 6 speed. The transmissions didn't seem to mind it, but both seemed to shift marginally worse than with the XT-M5 or Redline fluids.

Street car, but ill chime in.
One bottle each of mt90 & light shockproof in the [6 speed] trans and redline 75-90gl5 & heavy shockproof in the diff (rx7 housings take more fluid)
Gear whine and loud shifts in 1-2 when cold but no grinds. Reverse picks and chooses if it works the first time but thats expected.

I have the motorcraft miracle fluid in my cart on rockauto but havent really felt the need to switch yet.

I'm also on the motorcraft sauce. it shifts great, was a huge improvement over the generic stuff that came out of the box. I also run it in my Mazda b2600i pickup truck, and 323GTX gearbox, both of which come from the era of "brass syncros" that the ford fluid is good for.