I currently own a 99 civic ex 98,000 miles. Basic mods I/H/E and a skunk 2 short shifter. When shifting into second or third gear hard it grinds and both gears tend to just "pop" out. Third gear will do it from time to time but second gear will always do it when my foot is off the gas. So in other words when i am decellerating in second it just pops out. My guess is that the tranny is shot but i was wondering if anyone has any ideas or solutions being that i am trying to sell this soon. So my main goal is to get the tranny fixed and get rid of it. Thanks

 

If it's popping out of gear, it can likely be a shift fork.

For the grinding, that can sometimes be a shift fork, sometimes synchros.

Just for safe measures, check the fluid level in the tranny. If it's dirty replace it. You could also try GM Synchromesh MTF and it might help.