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Discussion Starter · #1 · (Edited)
Car is a 2015 Si

Hey all, I've been having some problems shifting from 1st >2nd and 2nd>3rd while above 6500 RPM. I have to really force it to come OUT of gear, and it will also occasionally grind while going IN to the next gear. If I clutch in and just wait for the RPMs to fall a bit, it'll pop out nice and smooth as soon as the tach dips below 6500. It's been doing it for a few months and I've mostly been ignoring it, but I feel like I eventually need to address the problem.

Mods on the car that might have relevancy:
-Sirimoto N1 master/slave clutch cylinders
-Clutchmasters FX350 clutch with stock weight steel flywheel
-Acuity shifter bushings
-Acuity short shifter assembly

Minor fixes I've done that haven't solved it:
-Changed tranny fluid
-Changed clutch fluid and bled the clutch line
-Adjusted master cylinder and pedal to give it a longer disengage length

I'd appreciate any suggestions. I'm thinking maybe bad synchros but it also has serious problems getting stuck in gear (I have to really jam it to get it into neutral unless I just wait for RPMs to drop) and from what I understand synchros wouldn't affect this.
 

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Photoshop Masta
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When did the issue start happening? Did you notice it after any specific mod was done?

But, it does sound like a trans fluid issue.
 

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if you double or triple press (2-3x) your clutch pedal before shifting does it help ?

that would indicate synchros
 

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Discussion Starter · #6 ·
if you double or triple press (2-3x) your clutch pedal before shifting does it help ?

that would indicate synchros
Gonna be kind of hard to double press while holding it close to redline in 2nd gear since the problem only shows itself at high rpm but I can try lol

When did the issue start happening? Did you notice it after any specific mod was done?
The last mod I had installed was shifter bushings, but it didn't start happening until a few months after so idk if it has to do with that. I might try switching back to OEM bushings if I can find them.
 

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Photoshop Masta
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The last mod I had installed was shifter bushings, but it didn't start happening until a few months after so idk if it has to do with that. I might try switching back to OEM bushings if I can find them.
I doubt it's the bushings, you would've likely noticed an issue immediately.

When's the last time you changed your trans fluid?
 

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Discussion Starter · #8 ·
I doubt it's the bushings, you would've likely noticed an issue immediately.

When's the last time you changed your trans fluid?
3ish months ago, changing the trans fluid was the first thing I tried after I noticed it happening. I've never used anything except Honda MTF though, do you think I should try a different brand?
 

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Photoshop Masta
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Could be synchros issue if you changed your fluid recently, or even the slave/master cylinders. There's so many components that work together.

I have heard of issues with certain fluids. When did you upgrade your cylinders? How many miles would you estimate you've put on the car since?
 

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Discussion Starter · #10 ·
Could be synchros issue if you changed your fluid recently, or even the slave/master cylinders. There's so many components that work together.

I have heard of issues with certain fluids. When did you upgrade your cylinders? How many miles would you estimate you've put on the car since?
Timeline is as follows:
January 2020 : clutch master / slave.
July 2020: New clutch kit installed
October 2020: shifter bushings installed
January 2021: the problem first appears (or at least it's the first time I notice it)
Over the next month I changed all the fluids, bled the clutch line, and adjusted the pedal, problem persists.
April 2021: Acuity short shifter installed. Problem persists
So probably around 20,000 miles or so on the cylinders. Not brand new but also not a lot of miles on them. Another thing me and a buddy tested was to bang off launch control at 5000 rpm while the car was on jack stands and in gear with the clutch pedal fully depressed to see if the wheels spun at all and they didnt, so I'm pretty sure the clutch is disengaging properly.
 

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Photoshop Masta
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Timeline is as follows:
January 2020 : clutch master / slave.
July 2020: New clutch kit installed
October 2020: shifter bushings installed
January 2021: the problem first appears (or at least it's the first time I notice it)
Over the next month I changed all the fluids, bled the clutch line, and adjusted the pedal, problem persists.
April 2021: Acuity short shifter installed. Problem persists
So probably around 20,000 miles or so on the cylinders. Not brand new but also not a lot of miles on them. Another thing me and a buddy tested was to bang off launch control at 5000 rpm while the car was on jack stands and in gear with the clutch pedal fully depressed to see if the wheels spun at all and they didnt, so I'm pretty sure the clutch is disengaging properly.
Damn. Well, I'd start off with the easiest (least expensive) fix first and work my way up.

Trouble shifting gears is symptom of a bad slave cylinder, so are bad synchros but you'd be grinding gears more often than them sticking, so I'm leaning towards a bad slave cylinder. Definitely not a lot of mileage, but it also depends on how hard you are on the trans and how you shift.

Try switching to a different fluid first.
 
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