Schaeffer Oil V-Twin Lube Primary Synthetic Plus
After years of recommending the same transmission fluid for the Spec Miata 5 speed transmission, Advanced Autosports has "shifted gears" and is now running a product from Schaeffer oil. Originally designed as a lubricant for Harley Davidson motorcycles, their "V-Twin Primary Case Lube" works better than anything I have found for the Miata transmission. The Primary case on a H-D trans is a multi-disc wet clutch system. Being a wet clutch, the fluid must provide lubrication and cooling to the chains, bearings, gears etc. While at the same time, not acting as a lubricant to the clutch discs. The Miata's brass syncro rings are similar in operation to the clutch discs on the H-D motorcycle.
Advanced Autosports has been testing this fluid since last summer. I have torn down multiple gear boxes after using the Schaeffer V-Twin Primary Lube and found reduced wear on shift forks as well as the brass syncro rings. The fluid has a different feel that is hard to explain. Very smooth and slippery when rubbing your fingers together, yet with a sticky feel when separating your fingers. From the driver's seat the transmission shifts very smooth, eliminating any notchy feeling when cold.
Advertised as a 30 weight oil, we have not seen any horsepower loss when doing dyno testing. In fact the last two June Sprints race winners have had Schaeffer V-Twin primary Case Lube in their transmissions.