Question about 5th gear synchro and high RPM shifting

Hi everyone,

I just wanted to know if high RPM gear shifting is bad for the transmission synchros. I recently bought a used car and I’ve been a little OCD about checking the 4th to 5th gear upshifts to make sure there are no grinds since 5th gear is usually the most common one that goes bad in manual transmissions. I must have done a few hundred up shifts between 4-5k rpm (7500 redline) but I did them with proper form (didn’t slam the gear, didn’t shift super fast) and I moved the shifter up from 4th, to the right and all the up into 5th rather than the diagonal shift people like to do. I never once heard or felt a grind – it was quite smooth actually.

But it got me worried that I might have accelerated synchro wear with the high RPM shifting. Could it have even though it feels perfect to me? Again, I never skipped gears or shifted fast or slammed the gear in.

Thanks in advance

As long as there's plenty of gear oil in the transmission you should be fine it's kind of hard to tell since manual transmissions don't usually have dipsticks. It's also a good idea to change the gear oil every 20,000 miles or so. If you're worried about your gears, you can also drain the oil, pour it through a coffee filter and check for metal shavings.

Thanks for the feedback. Gearbox has full tranny oil. Could those repeated higher rpm shifts from 4-5th have caused accelerated wear? They went in fine all times, no grinds, and I wasn't slamming the gear in or fast shifting it as well. Is that how synchros get ruined?

you can also switch to a synthetic fluid. they usually have better protection than the 80-90w oils. i have a sentra se-r that had a crunch going into 5th unless i granny shifted it, put in syncromesh and the crunch went away. as long as your not missing shifts or grinding the gears it shouldn't really matter what rpm your shifting at. but the brass synchros will eventually wear out but with normal use should last a long time