I bought a 1995 Nissan 240sx s14 a month ago.(146K milage). It has a manual transmission. It didnt have any problems when i bought it. But right now when i try to up-shift from 1st gear to 2nd gear or 2nd gear to 3rd gear, it does not go in smoothly, instead it kind of grinds. I mean the gear still goes in and the car runs smoothly. But when i move the shift knob, i can feel that the gear grinds( for like half a second) before they got engaged together. It happens quite frequently. I would say 8 out 10 times. It is fine sometimes though. I am pretty sure that i did step on the clutch all the way before i shift and i usually shift at 3000rpm. Please tell me that if the clutch is too old or the transmission has problems.( I dont know how old the clutch is because the previous owner does not have any maintenance records.)

The vehicle appears to be suffering from "Clutch Drag". This is often caused by insufficient disengagement of the clutch pack components. On the Manual transmission I would expect 1/4 to 3/8 inches of "Free Play" at the clutch pedal. The distance between the rest position, and when depressed the point of first resistance. Anything in excess of this, requires adjustment to the Pedal stroke linkage, to obtain that measurement.
If this cannot be achieved then, the only alternative is to replace the Clutch Pack and Flywheel Pilot Bearing. At the same time. As the vehicle has covered 140k miles, without positive service records, a Transmission OIl change would be in order too.
Regards,David

First replace the fluid as if its old will cause this. If that doesnt fix the problem then unfortunately you have bad syncros which means the transmission will need to be removed and serviced completely.