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3rd gear grind

340 Views 15 Replies 4 Participants Last post by  actionseeker
I just got this car and 3rd gear grinds going into 3rd but push past it 3rd gear works fine it is strange and could I use syncromesh fluid along with recline Mt 90
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could I use syncromesh fluid along with recline Mt 90
No, never mix gear oil unless it is an emergency. Use 2.3qt of the Valvoline Syncromesh filled from the correct plug on the distal end of the transmission. It is the plug with the large allen key hole in it. If you fill from the 21mm plug under the shift fork you won't be able to fill the trans all the way up to 2.3qt, which would certainly cause problems.
If you're topped up with a single type of gear oil then check your shift bushings in the engine bay. If original, they should be replaced with Brass Shift Bushings to remove any slop from the linkage. You may also consider a short throw shifter for more precise shifts. The C60 is notchy and not the most forgiving transmission, especially when it's cold. So if the car is new to you it may take a few more months of learning to drive it slow and smooth before you get the hang of it. I had a similar experience when I bought a XRS 4 years ago and I've been shifting my own gears for over a decade.
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.
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