Been grinding gears lately.

mostly at the track, both Road Atlanta and Daytona. 4th and 5th mostly.

changed trans fluid last year, Royal purple 75-90. It’s what I had on hand. That fixed the 3rd gear grind I was having when I first got the car.

clutch system is all new, from the master cylinder all the way to the disc. Bled before Daytona and RA with ATE super 200.

should I swap the fluid for Honda fluid?

or set my clutch piston to ensure full disengagement?

seems fine driving around town. Only time I have issues is when I’m shifting/reving hard on track.

 

I've been using Royal Purple Synchomax. It's been all good, but I don't track the car.

 

Definitely check the clutch pedal free-play, if you didn't do that when the new master was installed.

 

Correct Grease in all the correct spots and verify pedal adjustment…this should be done #1. Clutch fluid, verify no Internal master cylinder leak. Not sure if 90w is helping or hurting you

 

I like where the free play is now but I can probably take some out. Thants probably it. Thanks

 

Correct freeplay is 1/4", and all of it is inside mc. There should be zero play between rod and back of piston it presses against.

 

Before you adjust....what is your freeplay set to?

The only correct freeplay setting is 6mm (1/4").

More than that will move you toward grinding from incomplete disengagement.

Less than that will move you toward a slipping clutch from incomplete engagement.

75W90 is just the weight of the fluid. Its a little thick...but the fluid weight itself shouldn't cause a grind (within reasonable allowances).

However, if you are using 75W90 GL5 hypoid gear oil not meant for synchro's...that's bad, and will absolutely cause issues. Typically GL5 hypoid gear fluids are too slippery for synchros, and a lot will also damage brass synchros due to their EP additives for hypoid gear use.

You need a GL4 manual transmission fluid, or a GL5 specificially designed for use with synchronizers.

Honda MTF is the best overall fluid for street use. For track use, its also fine if you are OK with frequent fluid changes. The current Honda MTF (MTF2) is about a 70W75ish or 75W80ish fluid. Its a little on the thin side if you're banging the car out at a track for 15-20+ min sessions.

Or....Royal Purple Synchromax, Redline MTL, Amsoil MTF...all examples of usable aftermarket transmission fluids that should last longer and provide more high temp protection for track use, as compared to Honda MTF2. All of them are thicker than MTF2. But they're designed for synchronizers.

 

This was what I had on hand. 3rd gear was grinding when I bought the car so I wanted to change asap. This fixed the grind immediately.

Says it’s also good for trans, GL4 or 5


im going to adjust the free play, it’s certainly more that 1/4inch. Maybe 1”. That ought to fix it. If not, then I’ll try swapping to Honda MTF.

thanks for the feedback

 

RTFM It's not good for the gearbox. The car needs Manual Transmission Fluid (MTF) and there are many acceptable products including Honda's own MTF, Royal Purple, etc. Threads abound.

Acceptable, temporary substitute for MTF is 10W-30 motor oil, not GL5 gear oil.Royal Purple makes lots of lubricants. If you want Royal Purple MTF use this not hypoid gear oil (differential oil).



Currently in my gear box although I can't detect any difference from Honda MTF. Seems ANY MTF makes the box shift smoother immediately after the oil change.

Additives and viscosity matters. List of MTFs.

-- Chuck

 

1" of freeplay will definitely cause issues. Your clutch engagement point is probably pretty close to the floor.

The fluid you're using is non corrosive to synchros, but probably doesn't have the friction modifiers that a synchromesh fluid has. Royal Purple Synchromax is what you want, if you'd like to stick with RP.