Clutch Master Cylinder

Clutch Master Cylinder

A clutch master cylinder can be found in those clutches which rely on pressurized hydraulic fluid to operate. Instead of a clutch cable, they feature a master cylinder that forces hydraulic fluid into a slave cylinder when the clutch pedal is depressed, causing the slave cylinder to disengage the clutch by moving a special fork that pushes the release bearing.

Hydraulic release systems have been popular thanks to their ease of operation. A driver doesn’t have to push the clutch pedal harder and harder to overcome the spring pressure of the pressure plate, which usually takes lots of force. His or her hydraulic release system makes it easier to disengage the clutch, so the driver can enjoy the ride instead of training muscles.

A typical hydraulic clutch consists of a clutch disk, a pressure plate, a release bearing, a master cylinder, a slave cylinder, and several other components. Covered in special friction material, a clutch disk that sits on the transmission input shaft is pushed against the flywheel when the clutch is engaged. This happens thanks to a pressure plate that puts force on the clutch disk, causing it to spin together with the flywheel. When a driver needs to shift up or down, he or she steps on the clutch pedal, which, in turn, moves the piston inside the master cylinder, causing it to force hydraulic fluid into the slave cylinder. The latter pushes on the clutch fork, which then moves the release bearing that involves the pressure plate.

Since a clutch cylinder is subjected to high pressure, it is prone to fluid leaks, which can cause a variety of problems, including the following:

Hydraulic fluid leaks 

A master cylinder is usually placed close to a clutch pedal. That’s why, if your master cylinder begins to leak, you’ll notice marks of the fluid on your floorboard or your carpet. Check there if you have to top up the fluid on a regular basis.

Loose clutch pedal

A leaking clutch master cylinder can increase the free play of the clutch pedal (the distance it travels before the clutch is engaged) and make it loose or soft. Depending on your vehicle, the free play should be between 0.5” and 1.5”. If it is less or more than required, this can shorten the service life of your clutch components and cause shifting problems.

Hard pedal

If your clutch pedal is hard to press or it jerks, you might have a swollen seal or blocked compensating port in the cylinder, or a worn-out transmission bearing retainer.

You can’t go into gear

Your clutch relies on high hydraulic pressure produced by the master cylinder to disengage. If the clutch master cylinder fails, the release bearing will not disengage the clutch when you press on the pedal. As a result, you’ll experience shifting problems.

Clutch master cylinder repairing procedure

Replacing a bad clutch master cylinder is not a part of routine vehicle maintenance, so it’s better to leave this job to a professional. Before replacing the cylinder, your mechanic should inspect the clutch and the transmission to make sure the cylinder is the only source of the problem.

Once a new cylinder is installed, the mechanic must force all air out of the hydraulic system, which is usually more difficult than bleeding brakes as this may involve special equipment.

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