I just had a clutch job done on my integra about 2-3 days ago. Today was the first time i really drove long distance with the car. i took it on the freeway and i made it about 63 miles before it started popping out of 5th gear and going into neutral. I pulled over to the next exit into city streets and 1-4 shifted and stayed in gear fine. but when i throw it into 5th it will stay in gear for about 30-45 seconds untill it pops out again. i also noticed it would pop out when i hit a bump. but idk.... I had to drive all the way back home on 4th gear because i was afraid i was gonna wear something out. (i made the drive from the central valley,california to the bay area california. roughly about 2 hours away from each other. anyways could anyone tell me what could be the problem id appreciated it thank's.

 

Hey, I believe it is your 5th gear synchro. It will probably need to be replace.

 

I've seen this happen on a couple late 80s nissan pulsars. My dad had his replaced, another guy I know had his rebuilt. Mine is at 280k and I haven't had issues. However, I replace my fluid frequently.

 

Synchronizers affect your ability to get into gear, they don't cause pop-outs.

 

Sounds like you either did something wrong when you changed the clutch, or your input shaft bearing just happened to go bad at the same time.
I'd check the shift linkage, and make sure the clutch slave cylinder is not pressed down on to the fork when your foot is off the pedal.