I hear that syncro grind noise when shifting at high rpm too fast into 4th. I have to wait almost 1 full second before pulling 4th if I'm up to 5.5k or itl buzz. The wilwood master cylinder fixed the high rpm lockout with my spec 2+ and really made it sweet. CDV delete helped too I think but I have to be easy and slow into 4th.
Have you tried changing the tranny oil? I had a similar result. I had my CMC adjusted at the dealer and it solved the 1st to 2nd grind but didn't fix the 3rd to 2nd downshift. I read somewhere that at the factory some trannys weren't filled with the right amount of oil and was way too thin. So I went to the dealer again to change the tranny oil, no additives or different oil. Just what the dealer would change it with. I did this so that if I had to go through warranty to get my tranny replaced that it shows that I am going through the process. Well.. since the changing the oil the car shifts like butter and have not grinded once since then and it's been several months. The shifter now takes a little more effort to shift so I know that there is a lot more fluid to protect the synchros and prevent the grind. Try it!
Hey, did you ever fixed the grinding? My 2020 Si has been doing the same thing, it grinds in 4th at high rpms, I have to hold the clutch for a second, shift into 4th & let go for it not to grind, is it the synchros?
Yes, my 4th gear shift will still grind if I'm too quick at high RPM, or any RPM really. I'm sure it's the synchros taking a second to line up. I just take my time for 4th. I changed to amsoil Synchromesh at like 20k miles and to gm at like 40k miles. The second time I changed it, it still looked new vs the OEM fluid at 20k was dark. I think the gm is better but my 4th gear grind is the same either way.
