transmission probelems. 5th gear.

[pancho y onions]

I got a 91 240sx HB. Here is the probleme.

Well for some reason it does not lock into 5th gear. I would think 5th gear would be the last to go out. I was hoping it might be the shifter bushing, so i changed it. It goes into 5th gear now but i have to really push it in hard and while pushed in i let go the clutch or else it just grinds. So im pretty sure its something different and not the gears. But once its in i cant let off the gas cause then it doesnt stay in gear like it pops out. And if im on a bumpy road it pops out again. It seems like it doesent lock in all the way like the other gears. I can feel a differnce too when i try putting it in 5th, like it doesent engage all the way. so if you guys can help me out that would be cool. Thanks

[pancho y onions]

Oh yeah and when i do have the car off it still wont go all the way in.

[zerepdivad]

bump

[geddis]

on my gearbox the main shaft retaining nut came loose cause that problem