So I have noticed lately that when I shift into 3rd it grinds. I know that honda is known for the 3rd gear grind but i didnt know 4th gear as well. I have a b20b motor with b16 trans. It does not pop out or anything just makes nasty sound when I shift. Would that penzoil synchromesh temporary fix both gear grinds or is it something else? It is like the shifter is not lining up probably and if i do it slow its fine.

 

it maybe as simple as bushings on the shift linkage, or a crappy short shifter. It also could be the syncros inside the transmission. I'd start small and cheap and worst comes to worst open it up and rebuild it all since your opening it up. I personal don't run anything but honda MTF if your putting anything else in there on a stock power set up you're just hiding a problem that not can, but WILL get worst if put off

 

Check the shift linkage for any play, but i wold bet on synchros - het the synchrotech ones - i had the same issue, replcaed with 3 and 4 synchro from synchrotech and problem is gone - don`t wait too long with fixing the synchros since it can beat up your gears as well !

 

Majority of the time it is the selector sleeve that wears down. Replacing just synchros with a bad sleeve will only mask the problem temporarily. When one side of the sleeve for 3rd is damaged it makes it hard for the opposing side to engage 4th since the sleeve does not slide smoothly on the center hub. You will also want to check the synchro teeth on the gear as well to make sure they are not smashed or rounded over. 3/4 sleeve set is a common replacement item in B series transmissions. As mizerb16 stated...the longer you wait, the more damage that can be caused. I would also check your 3/4 fork for wear.