I drive a 1993 civic ex, d16z6 5 speed. Recently, my car started being difficult to downshift, even with the clutch pedal all the way depressed. Occasionally it's difficult to shift up as well. It seems as though the clutch is not disengaging fully,but my shifts don't grind at all. My dad thinks it could be the throwout bearing, but I don't hear any squealing when the clutch is engaged, nor whe the pedal is fully depressed.

 

check the clutch fluid

 

Clutch fluid is full.

 

shifter bushings? try some energy ones.

 

Try draining the transmission fluid and refilling with a Honda-recommended MTF.

 

Also, when I'm sitting still, car in gear, clutch in, sometimes my RPMs dip low enough that there's some rumble throughout the car. This goes away as soon as I take it out of gear. Any ideas?

 

Try bleeding the clutch master and slave cylinders to purge any air and also to replace your really old fluid.