My fourth gear in my transmission has been stubborn for a little while now. It's an old b16 transmission so I replaced a few parts to get me by and make it a working transmission again but I could never afford synchros or sleeves but plan on it this winter.

When I'm driving, I can shift into all the gears real nicely, but 4th gear sometimes doesn't go in all the way I'm assuming. The thing that makes me think it is probably the synchro is that when I shift into 4th at 3k rpms and slowly put it into 4th, it almost always goes in. between 3 and 4k rpm's, it doesn't really go in but all rpm's higher than that, it almost always goes in again.

A couple of times when I have been in 4th and taking turns, it has popped out which seemed like something like a mount but the whole rpm thing throws that off.

Anyone got any ideas and think it's probably sycnhro related

 

Synchro could be worn, synchro ring needs to be replaced. 3/4 hub/slider and 4th main questionable.