3rd gear grind

actionseeker said:

On our transmissions, a Redline MT-90 and Syncromesh blend is very commonly done due to the issues that newer GL-5 gear oils present for our gears. TL;DR, the new stuff has high amounts of sulfur, which eats our brass synchros. This made it so people had to find an equivalent GL-4 oil that was free of sulfurs. MT-90 worked best, but was well known for being pretty notchy while cold, so often people would blend in a bit of Synchromesh to allow better cold shifts. This is the mix I use as well, and it's done nothing but good for me. I run a 1:3 ratio of Synchro to MT, and at the very least it made the grind a bit smoother and allows me to granny shift without grinding.

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Valvoline is one of the most reputable lube makers in the world. Here is what they say about Synchromesh MTF. I also pulled up the MSDS for Synchromesh and did a quick Crtl+f for "sulfur" and found no mention. The additives and quantities used in these oils are guarded industry secrets, which is why I don't like mixing oils that engineers w/ PhDs and millions in R&D money carefully designed. Who knows what chemical reactions or decline in operation parameters might come from mixing different additive packs? I have no idea bc I didn't go to school for cheimical engineering and I don't want to find out. Do whatever works for you, but I wouldn't do it becuase of anecdotal advice.

Edit: I've been running Synchromesh in my 175k C60 for 3 years after I used MT-90 the first year because it worked great in my C59, but I was still having gear clash in 3rd and 5th. This last year of driving I have had no clashing and once warmed up I will catch lift from 2nd-5th gear 3-5 times per day with buttery ease. I do have brass shift bushings and the MWR shoft shifter with a weighted knob. That's just my anecdotal experience.