My 98 civic dx clutch pedal is popping of the floor. If i pump the clutch a few times i can shift gears ok while driving through town. Once i get on the highway and get into 5th gear and drive alittle i can't get shift out of 5th gear without pumping the clutch. The master cylinder is full and i don't see any leaks anywhere in plain view. What could be going on or what should i check next? Slave cylinder?

 

The master cylinder is worn out. Replace it.

 

Is there anyway to be sure?

 

How is the rod connected to the clutch pedal?

 

If it's not leaking at the slave cylinder, and it's not leaking into the engine bay at the master cylinder, get in the drive'rs side footwell, and shine a flashlight up the clutch pedal/lever assembly. You may see it leaking there (and spilling onto the carpet). If not then, like mk378 said, it's probably the diaphragm inside the master cylinder that's toast.

 

Have someone step on the clutch while you watch for movement of push rod on the slave cylinder. Keep pedal steady on floor, see if the push rod maintains its position or gradually retracts.

 

There is grease coming out of the master cylinder under the dash

 

Your master cylinder is dead. It is a fairly simple job to do IMO. Google for a few DIY guides on installation and bench bleeding.

 

Is bench bleeding really neccessary? How would you even bench bleed it when the fluid resevoir is not part of the master cylinder? After looking at it, it will be fairly simple to replace, just a PITA crawling under the dash.

 

Gooooooooogle. Sry to sound like a dick, but bench bleeding is an extremely common concept and practiced on most all vehicles. The reservoir is technically a part of the CMC, just attached with a hose.

You do not HAVE to to it, but without bench bleeding, you will be bleeding the clutch fluid for a lot longer until all of the air is out of the new CMC.