Your guide to clutch faults – Part 2
An ailing clutch can be expensive to repair but Rob Marshall explains the high labour charges involved with a clutch change and advises on how to prolong its life.
Despite being so essential, the clutch comprises of just three parts, known collectively as a clutch kit. A friction plate is clamped against the engine’s flywheel by a pressure plate and released by a release bearing. As the friction plate is connected to the gearbox, it can be clamped firmly, disconnected entirely or an infinite amount of “slip” can occur against the flywheel’s face, so that the car can move away progressively. The release bearing acts by either pushing or pulling the pressure plate, to disconnect the drive.
The components of a typical clutch kit.
Changing the clutch kit often dictates that the heavy gearbox is removed first. This explains why the labour charge often exceeds the price of the clutch kit.
PROBLEMS WITH THE CLUTCH KIT
As the clutch kit’s friction plate possesses friction linings, ‘slipping’ the clutch hard at high engine speeds causes the linings to vaporise and hastens the need for a clutch change. In advanced stages of wear, clutch slip can occur with the pedal released and, if it is ignored, the clutch could not only fail to transmit any drive whatsoever but also flywheel damage could result. Clutch slip might occur if the friction plate becomes contaminated with oil, such as from a failing engine or gearbox oil seal.
If a clutch’s friction linings wear out completely, through excessive clutch slip, the plate’s metal backing will grind into the flywheel’s surface, which could add to the repair cost.
The pressure plate’s springs can weaken with time and cause clutch slip, although it is almost impossible to identify this visually. The release bearing does wear and, in extreme cases, will squeal when the clutch pedal is depressed. Never apply pressure to the clutch pedal continuously while driving and do not hold the clutch pedal down for long periods of time.
As clutch life is so dependent on driving style, most car manufacturers refuse to cover the cost of replacing clutch kits under the terms of their warranties. Under normal use, a clutch should last between seven and ten years but, when the time comes to replace it, the entire clutch kit must be replaced. Some models also require several additional parts to be changed at this point.
As a clutch change requires significant dismantling, in order to access the clutch kit, it is normal for workshop labour costs to eclipse the parts bill. Still, before committing to an expensive clutch change, ensure that the fault is not caused by the operating mechanism.
A dual-mass flywheel (pictured above), compared to the conventional item
A sectioned dual-mass flywheel.
Since their adoption by most manufacturers, primarily for their diesel models, a dual-mass flywheel (DMF) differs from the more conventional ‘solid’ type, by having a flexible damper built within it. Intended to absorb stresses from the engine and transmission, they can fail prematurely, causing a metallic ‘clanking’ sound and/or vibration to be felt at certain engine speeds. It is recommended by many technicians that dual mass flywheels are replaced at every clutch change. Still, excessive clutch slip can put undue stress on the dual-mass flywheel and reduce its operating life.
Once the work is completed, ensure that the clutch works correctly and that the gears can be selected easily from a standstill.