AS the title states, my tranny on my 02 WRX grinds when I shift into 4th gear (from 5th or 3rd) when I'm spinning above 2-2.5kRPM. I know what caused it (don't ask) but I'm kinda curious exactly what it is.

IS it synchros (bad, but not terrible IMHO) or is it gears (Bad bad bad). There are no other audible or physical (shudder or what not) signs after the shift, it is only when changing gears.

It has been doing this for about 3 months without getting worse, but I am curious.

Thanks.

edit: BTW, I am running AMSOil 75W-90 synthetic gear lube in both the tranny and rear diff.

 

Synchro, no doubt about it. Try regular dino oil in the tranny to see if that makes a difference. Otherwise, sharpen up your double-clutching skills.......

 

do regular part stores sell the dino gear oil. i put in royal purple and am regretting it. I get an almost chattering sound when slightly lifting off throttle, but not enough to start deaccelerating. Is this a sign of the synros going bad because of the synthetic oil?