Best trans fluid for synchro grind?

[e30mitch]

Hello All!

My transmission sometimes grinds when going into 3rd…I currently have new gear oil in there (Red Line full synthetic 75w90). Is there another oil that may help ???

Thanks!

[It's Soda Not Pop]

thats the fluid I use as well. Every once in a blue moon mine will grind going into to third on the upshift. Most of the time I slow down just a bit prior to shifting which works.

[It's Soda Not Pop]

My buddies vert does the same thing every once in awhile as well.

[reelizmpro]

Why not MTL (75w80)? That's been the go to for decades.

[lukeADE335i]

I run Redline MT-90 (75W90) as it’s the same viscosity as BMW recommends stock. People have been running MTL for decades without any issues and you can’t go wrong with the Redline MT fluids, maybe the thinner MTL will help?

In the e92 I run Redline MT-LV (70W75) and that has also been excellent - this is what Redline recommends for the GS6-37 transmissions.

e30Mitch - are you running MT-90 or the 75W90 gear oil? If it’s the latter - the 75W90 gear oil is GL5 for diffs rather than GL4 for transmissions. That might effect your synchros?

[bmwman91]

I switched from Redline MT90 to this Motul stuff last year and I feel like it shifts better cold, is slightly less noisy overall (input shaft rattle), and generally seems like the better option for old high mileage transmissions like mine.

https://www.motul.com/us/en-US/products/gear-300-75w90

They also make this stuff which is recommended for noisy gearboxes, whatever that means. It might be worth looking in to as well.

https://www.motul.com/us/en-US/products/gearbox-80w90

Both are rated as GL4 AND GL5, so you can use them in transmissions and diffs. I also use the Gear-300 stuff in my Wavetrac diff since it is what the manufacturer recommends, and it is how I "discovered" the stuff in the first place.

[It's Soda Not Pop]

I switched from Redline MT90 to this Motul stuff last year and I feel like it shifts better cold, is slightly less noisy overall (input shaft rattle), and generally seems like the better option for old high mileage transmissions like mine.

https://www.motul.com/us/en-US/products/gear-300-75w90

They also make this stuff which is recommended for noisy gearboxes, whatever that means. It might be worth looking in to as well.

https://www.motul.com/us/en-US/products/gearbox-80w90

Both are rated as GL4 AND GL5, so you can use them in transmissions and diffs. I also use the Gear-300 stuff in my Wavetrac diff since it is what the manufacturer recommends, and it is how I "discovered" the stuff in the first place.

I think I'm going to switch to this fluid next round that I do a fluid change. My tranny is noisy.

[moatilliatta]

The wrong gear fluid will grind.. So try ATF or MT-LV Or BMW MTL2.