Hydraulic clutches for manual transmissions use brake fluid to supply pressure to disengage the clutch from the engine. Pushing in the clutch pedal makes fluid flow from a master cylinder (or fluid reservoir) to the slave cylinder, which moves the pressure plate, allowing the driver to shift gears. Seals and hoses can leak, and if enough fluid doesn’t reach the slave cylinder the clutch pedal may go all the way to the floor or the driver may not be able to shift gears. Air can also get into the hydraulic system, causing the clutch pedal to feel spongy. Some slave cylinders are mounted on the outside of a manual transmission, while others are inside the transmission bell housing.