Clutch Master or Slave Cylinder
 

I have a 92 Civic Vx, which refuses to get out of neutral. The transmission shifts fine, but the pedal will not allow me to change gears. What is the best way to diagnose this btw the car has 280,000 km

first pull back the slave boot, see if its leaking. If it is, change it.

Then check air in the system.

follow up
 

There was no leaking after pulling back the boot, and I bled the sytem, so the pedal has a good feel, any other suggestions

...

have someone press the clutch pedal while u look to see if the slave is actually moving the shifter fork

if not the the seals have gone in the cylinders and u need new ones