The clutch master cylinder in your Ford Focus transforms the pressure you apply with your foot on the clutch into hydraulic pressure. This pressure then travels to one or more slave cylinders, which in turn facilitate the shifting of gears in the transmission. If the clutch master cylinder goes out, you will lose the ability to shift gears. The clutch master cylinder replacement procedure can be time consuming, due to the fact that it is located opposite the clutch pedal along the firewall beneath the engine.
Open the bonnet, and disconnect the negative battery cable from the car battery using a ratchet and socket. Climb into cab and set the front seat back to make room for accessing the dash.
Unscrew and remove the lower dash using a Phillips screwdriver. Locate the diagnostic connector, which is directly behind the lower dash panel near the right side of the steering wheel. It is a black, double-ended cord with ends similar to those of a USB cord. Unplug both ends. Pull one end out by hand, then unscrew the two thumbscrews on the other end, and pull it out.
Line the floor beneath the clutch pedal with rags, which will absorb any hydraulic fluid that might spill while replacing the clutch master cylinder. Raise the front of the car with a jack, then allow the car to rest on jack stands.
Climb beneath the vehicle and locate the main hydraulic fluid hose along the firewall on the other side of the clutch pedal. It is connected to the topmost pipe in the firewall. Locate the hose retaining clip on top of where the hose connects to the firewall. Remove the clip by hand. The other end of the hose is attached to the clutch master cylinder. Remove the pipe fitting from the clutch master cylinder with an adjustable wrench, and plug the opening with a rubber plug. Remove the other end of the hose from its connecting pipe in the firewall by hand.
Locate the secondary hydraulic fluid pipe just below the main one along the firewall. Pull the retaining clip from the pipe by hand, then unfasten the small pipe fitting from the mater cylinder with an adjustable wrench, and plug the opening with a rubber plug. Pull the other end of the hose of from its pipe connector in the firewall by hand.
Locate the clutch master cylinder's pipe flange along the firewall, then climb into cab and access the nut that connects the pipe flange to the firewall through the lower dash. Remove the connecting nut using a ratchet and socket, then unscrew the flange with an adjustable wrench.
Climb back under the car and unbolt the clutch master cylinder from the pedal bracket using a ratchet and socket. Pull the retaining clip from the clutch master cylinder by hand, and pull the cylinder out of the retaining clip sideways. Remove the piston rod from the top of the pedal bracket by hand, then pull the master cylinder out of the footwell.
Fill the new clutch master cylinder with hydraulic fluid, then slide it into the retaining clip sideways, and fasten the retaining clip by pulling it forward over the cylinder. Reattach the piston rod to the pedal bracket, then reconnect the pedal bracket to the cylinder with a ratchet and socket.
Climb into the cab and refasten the pipe flange with an adjustable wrench, then reconnect the connecting nut with a ratchet and socket.
Reconnect the smaller hydraulic hose to the master cylinder and firewall connector, then reattach the pipe fitting to the cylinder with a ratchet and socket. Refasten the hose retaining clip to the hose's firewall pipe by hand.
Reconnect the main hydraulic hose to the master cylinder and firewall connector, then reattach the pipe fitting to the cylinder with a ratchet and socket. Refasten the hose retaining clip to the hose's firewall pipe by hand.
Climb into cab, then reconnect the diagnostic connector, and reinstall the lower dash. Reconnect the negative battery cable with a ratchet and socket.