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Your Clutch master cylinder worn out? » Read more about common malfunctions • Repair • Replacement manual
Transmitting the hydraulic power: the master cylinder
The master cylinder is part of the clutch hydraulics, connected to the clutch pedal with a cable and a lever mechanism on one end. The hydraulic line on the other end leads to the slave cylinder. The slave cylinder is responsible for clutch disengagement.
Construction and location of the master cylinder
The clutch master cylinder sits right in front of the clutch pedal on the engine side, usually screwed onto the bulkhead. It can also be fixed to the gearbox. The master cylinder is a simple hydraulic cylinder. Stepping on the clutch pedal compresses the hydraulic piston in the cylinder, which in its turn compresses the hydraulic fluid. This pressure is transmitted to the slave cylinder via a metal pipe. The slave cylinder extends a rod and by doing so disengages the clutch. A return spring causes the master cylinder and the clutch slave cylinder to resume their original position when the pedal is released.
Advantages of the construction
The hydraulic power transmission allows the builders to position the clutch and the clutch pedal relatively randomly. Due to the hydraulic bypass, master and slave cylinder can be put in random order and just as randomly far or nearby. Furthermore, the hydraulic power transmission allows for a power boost through cylinders with different diameters. This enables within certain limits the use of large and slow clutches without additional power boost.
Clutch master cylinder defects
A defective master cylinder can be identified in different ways:
- No resistance from the clutch pedal
- Clucking or hissing sound when engaging the clutch
- Oil patches under the car
- Heavy gear shifting and engaging clutch.
A visual check can identify oil leakage from the master cylinder or a porous hose. This is a serious defect and compromises traffic safety. It should be repaired as soon as possible.
Usually, clutch master cylinders have a long life span. They should be checked on occasion of each clutch replacement. A failure of this component normally does not occur before the 200.000 km mark. However, the individual driving style strongly influences the wear of a clutch master cylinder. Short distances and urban traffic cause more strain to the clutch master cylinder than long stretches on the motorway. Replacing the entire clutch system in case of damaged hydraulic clutch component is always the better option. Master cylinder, slave cylinder and the connecting hydraulic line are always equally strained and therefore wear simultaneously. When a master cylinder fails, the slave cylinder is bound to follow soon. You save a lot of work and money by simultaneously replacing all parts. In addition to the correct installation of all components and the change of all gaskets, venting/bleeding is very important. The hydraulics transmit power by way of fluids. They only function when there are no air bubbles in the line. Unlike liquid, air allows compression. An unvented hydraulic clutch line would considerably impair its functionality. Installation is not very difficult and speaks for itself. Be sure to clean the engine thoroughly prior to repair. This prevents dirt from penetrating the lines and allows you to spot leakage better. After removal of the old parts all points of contact should be thoroughly cleaned again. This helps installing the gaskets correctly and assists adequate sealing of the system. The venting/bleeding procedures may vary. In some cars the system, bleeding is done by way of the master cylinder, in other cars by way of the slave cylinder. Consulting a repair manual is indispensable in this case. With a bit of skill and exercise this repair can usually be performed by an experienced DIY'er. It is important to ensure full sealing and tightness of the clutch hydraulics after repair.
Costs for a clutch master cylinder
A high-quality branded component from LuK costs ca. 60 EUR (± £53). For a repair of older cars in consideration of their market value, cheaper spare parts can be used. Nevertheless, only branded articles from the professional trade should be used. Amazingly, prices for the master cylinder vary greatly, reaching from 30 EUR until 200 EUR (± €26 - £180). The clutch pipe on the other hand is rather cheap with 30 EUR (± €26). Nevertheless, it is always worth while to replace the hydraulics of the clutch completely.