Your guide to clutch faults – Part 1
A clutch that will neither engage nor release correctly can not only damage your transmission but, as Rob Marshall argues, an incorrect diagnosis can also cause your wallet serious harm.
Rectifying clutch faults can be expensive, time consuming and inconvenient. On most front-wheel-drive models, replacing the clutch kit often requires the transmission and part of the suspension to be removed. On some cars, because space can be at such a premium, it means that a technician might have to remove the entire power-plant.
Before having the clutch kit replaced, which is likely to involve removing the gearbox, consider that the fault might be caused by the clutch operating mechanism.
Although clutch faults can be caused by the clutch kit being worn out, the problem could have a less complex and cheaper cause. ‘Drag’ is a typical clutch fault, where depressing the pedal does not release the clutch fully, which can result in noisy gear changes and difficult engagement of either first or reverse gears.
CLUTCH CABLE FACTS
While drag might have expensive causes, it is possible that the clutch fault is caused by the operating mechanism. Many models rely on a clutch cable, which can stretch, meaning that dipping the clutch pedal might result in an inadequate movement, within the engine bay.
A clutch cable can also snap without warning, rendering the pedal useless. As the clutch kit relies on friction to work, it does wear out gradually and so an adjuster is provided in many vehicles. Sometimes, an automatic adjusting mechanism is integral with the cable. Alternatively, clutch cable adjustment can be performed manually.
If either the manual adjuster needs attention or a clutch cable’s automatic adjuster fails, then the clutch could slip. This means that, under hard acceleration with the clutch pedal released, the engine revolutions will rise, without the road speed increasing accordingly. Clutch faults like this can result in the expense of replacing the entire clutch kit, when only the clutch cable needed either adjustment or renewal.
Some car manufacturers use hydraulics instead, where a clutch pedal operates a piston within a master cylinder, which forces hydraulic fluid through a flexible hose to a clutch slave cylinder. This pushes against a lever that operates the clutch. The advantage with hydraulics is that they often eliminate manual adjustment.
Any hydraulic fluid around the clutch slave cylinder body or surrounding pipework may indicate a leak.
The components within a typical clutch slave cylinder.
Unfortunately, the internal seals can fail in both the master cylinder and the less complex clutch slave cylinder, which either permits fluid to escape or air to enter the system. These conditions will cause clutch drag. On some models, the clutch and brake systems share the same fluid within one reservoir. Still, the hydraulic fluid is hygroscopic and so the fluid should be flushed through the system every two years. The process will also ‘bleed’ out any troublesome air bubbles.
Some hydraulic systems have their own separate reservoir, which is integral with the master cylinder’s housing.
The components within a typical clutch master cylinder.
Should either a clutch master cylinder or clutch slave cylinder fail, they are often replaced. For older cars, where new parts are obsolete, seal kits are often available.
Therefore, when a clutch fault is detected, it is worth inspecting the condition of the clutch operating media first, before committing to an expensive repair bill, when it could be unnecessary.