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Safety Checks - Clutch

All vehicles with a manual transmission will have a friction clutch between the engine and gearbox, allowing the driver to pull away from a standstill and change gears. Advances in manufacturing techniques and modern materials mean that clutches are much more hard wearing, but still need periodic inspection and replacement as the friction material wears.

Worn clutch symptoms

The most common problem with clutches is the wear of friction material. Worn friction material can cause the clutch to slip, and eventually will lead to a lack of power transmitted from the engine, through the transmission and to the wheels.

The clutch will only wear while the clutch disc and the flywheel are spinning at different speeds, in other words, during take up of drive or during an up or down shift. When they are locked together, the friction material is held tightly against the flywheel, and they spin in sync.

Modern electronically controlled manual gearboxes such as ZF AS-Tronic are designed with a conventional clutch pedal, to take up drive and change gear automatically without the need for physical driver input.

While this takes the onus away from the driver somewhat, to prevent unnecessary loading of the release bearing care must still be taken to ensure the gearbox is not in drive whilst standing in idle for long periods.

Symptoms of a failed release bearing or worn friction material differ depending on vehicle type and specification. A vehicle equipped with an electronically controlled transmission may de-rate the engine via the drive line network when the software detects the problem. As a result, a symptom could appear to be reduced engine power; warning lamps and fault codes would usually be displayed in this case.

Correct diagnosis

Correct operation of an air-assisted clutch system relies heavily on the quality and pressure of the air supply. A system that has been contaminated with water or debris or one with incorrect pressure can also cause symptoms of clutch failure.

Clutch replacement is an involving job, requiring removal of the transmission to access the clutch. Unless you are an experienced in this area it would be advisable to book your vehicle into a specialist to have the work done