Clutch Slipping: Symptoms and Causes

Does it seem to you that your vehicle is accelerating slower than usual and struggling to get up hills? Do not rush to look for faults in the ignition or fuel supply: if these symptoms are accompanied with free play in the clutch pedal and there is an unpleasant burning smell in the passenger compartment from time to time, it is likely due to a slipping clutch. We will explain why this occurs and how to avoid it.

How is a car clutch designed?

The system is designed to smoothly disengage and engage the engine and transmission at certain moments, i.e. when shifting gears, pulling out, or braking. Today the most widely used design is the friction clutch, where the torque is transmitted as a result of frictional force. The key components of the unit include:

• The clutch cover assembly. It consists of a pressure plate, a cover, and a diaphragm spring. The cover is firmly bolted to the engine. Special springs are used for connecting the cover and the pressure plate. When the clutch is engaged, they are pushed together; when the clutch is disengaged, they are released and the pressure plate is pulled back from the driven disc. The pressure plate is activated using the diaphragm spring. When the clutch is engaged, its fingers press the pressure plate against the disc, which in turn pushes the driven disc onto the flywheel of the engine.
• The driven disc. It is located between the engine and the pressure plate. It is a metal disc with the friction linings attached to it by rivets. The inner diameter of its hub is connected with splines to the input shaft of the gearbox. Smooth gear shifts and vibration damping are ensured by damper springs. When the clutch is engaged, the component is pressed onto the flywheel, which transfers the torque from the engine to the transmission.
• Release bearing. It is located on the unit's rotation axis. It is designed to activate the damper springs. In some vehicles, a pull-type release bearing is used.
• Clutch release fork. It belongs to the clutch linkage, and enables the release bearing to move.

The system works as follows: when the pedal is pressed, the clutch release fork, which is actuated by the linkage, presses the release bearing, shifting it along the rotation axis towards the flywheel. The release bearing activates the diaphragm spring, which is compressed and pulled back from the surface of the pressure plate. Springs are released and, when uncoiling, they pull the pressure plate away from the driven disc. The driven disc then moves away from the surface of the flywheel. This means that the torque is no longer being transferred from the engine.

What happens when your clutch goes out while driving?

If the clutch fails while you’re driving, the transmission will be disconnected from the engine, meaning that there will be a sudden loss of power and the car will come to a stop. This can be very dangerous, especially if the power cuts out while accelerating in flowing traffic. Make sure to get it fixed as soon as possible.

What is clutch slipping?: its meaning

When the clutch slips, it means that it fails to disengage or engage the gearbox/transmission, causing the car to slip out of gear or difficulties switching and staying in gears. It can occur as a result of wear, leaks, and poor adjustment.

What does a slipping clutch feel like?

You may hear an abnormal grumbling, grinding or squealing noise when you press down on the clutch pedal. You’re also likely to experience a sudden loss of acceleration and the pedal may feel loose or spongy.

Clutch slipping: symptoms

Don’t miss the main clutch slipping signs which indicate that it’s time for a replacement. Replacing the parts before the unit fails completely will enable you to avoid serious road accidents.

Common symptoms of a slipping clutch:

• High engine revs with decreased speed: when accelerating, the engine revs increase disproportionately to the vehicle's speed.
• Difficulty shifting gears: it may feel more difficult than usual to change gear and there may be resistance or grinding when attempting to engage a gear.
• Smell of burning: you may notice a burning odour similar to burnt toast, especially during rapid acceleration or when climbing hills.
• Loss of acceleration: despite pressing the accelerator, there may be a lack of power or sluggishness, especially when driving in higher gears.
• A slipping sensation: the feeling of the clutch slipping or disengaging momentarily, often accompanied by a brief increase in engine RPM without an increase in vehicle speed.
• Clutch pedal feels unusual: the clutch pedal may feel softer, spongy, or looser than usual. It may also engage at a different point as the pedal travels.

Clutch slipping: causes

Clutch slipping can happen for a number of reasons, the main one being the general wear and tear of critical parts like the pressure plate, the flywheel, or disc. It can also occur as a result of fluid leaks, thermal damage, and an incorrectly adjusted hydraulic system.

The system’s operation depends on the frictional force between the driven disc and the flywheel. If the friction coefficient decreases for whatever reason, the contacting surfaces start slipping and the torque is not transmitted completely from the engine to the transmission. As a result, the vehicle requires more time to accelerate to certain speeds and its performance deteriorates. It also becomes more difficult to climb inclines and hills as the power transmitted to the shaft of the gearbox is not enough to move the vehicle.

5 most common reasons for a slipping clutch

• Worn, damaged friction linings and disc surface. Excessively worn friction linings: due to their reduced thickness, they are not pressed firmly enough against the surface of the flywheel. The mechanism’s compression is therefore not sufficient to provide a secure connection between the components. Deformed linings are pressed unevenly against the flywheel.
• Oily friction linings. This reduces the friction generated. Due to the low friction coefficient, the contacting parts slip.
• A weakened or damaged diaphragm spring. If the spring’s elasticity has decreased, the pressure exerted on the driven disc by pressing the pedal will be insufficient to activate the assembly.
• Clutch linkage malfunction. Clutch slipping may be caused by a stretched cable, a damaged fork in a mechanical clutch, swollen rubber components, or poorly sealed elements in vehicles with a hydraulic system since the pressure on the diaphragm spring is not sufficient to ensure secure contact between the parts.
• Damaged wear compensation mechanism. Due to a malfunctioning adjustment ring or sensor spring, clearance adjustment becomes impossible. This reduces the hold-down pressure of the driven disc.

Slipping clutch quick fix: is it possible?

Normally, it isn’t possible to repair the damaged or slipping clutch as the parts usually need to be replaced. In certain cases, a “quick” fix may be possible, such as when the hydraulics or clutch linkage needs to be readjusted or the flywheel needs to be resurfaced.

6 recommendations that will help you avoid clutch slipping

• Try to replace components of the system at the same time with a kit. The average service life of the pressure plate, driven disc, diaphragm spring, and the release bearing is approximately 100,000-150,000 kilometres of mileage. Therefore, to make the system work as long as possible, always replace the components together.
• Check the tightness of vehicle components and assemblies. Poor-quality or damaged engine and transmission gaskets, oil leaking from the input shaft oil seal or crankshaft seal, and a loss of tightness in the hydraulic actuator are all reasons why oil gets on the friction linings of the clutch.
• Choose parts based on your driving style. A standard clutch with a composite friction material will be fine for calm, smooth driving. The linings have the optimum friction coefficient and low operating temperatures, and are inexpensive. However, a sports car would be better suited to a high-performance clutch designed for heavy loads. Its linings are usually made of materials with added carbon and Kevlar, and it is made of a mixture of copper, aluminium, cast iron, and ceramics. The unit withstands much higher temperatures, has increased wear resistance, and is suitable for intense driving.
• Check and adjust pedal travel. Insufficient pedal travel prevents the clutch from completely disengaging. This causes accelerated wear of the friction linings, and may be the cause of overheating and a warped disc.
• Always use the transmission fluid recommended by the manufacturer. Do not mix different types of fluids. Harsh compounds formed as a result of mixing fluids or elements in a particular type of fluid may damage the hydraulic clutch actuator.

Stick to the following rules of clutch operation:

• When moving off, first bring the clutch pedal to the biting point so that the car starts off and begins moving slowly, then hold it down slightly for 2-3 seconds and only then release it completely.
• Do not pull out at high RPM.
• When going down a steep hill, put the vehicle into first gear and press the brake pedal every so often to prevent the components from overheating.
• When getting out of difficult off-road areas, for example, a deep puddle, a snow pile or mud, use a towing vehicle if possible.
• When driving, do not continuously rest your foot on the clutch pedal to avoid pressing it by accident.
• Do not overload your vehicle, especially when driving on poor quality roads. This greatly increases the load on the assembly.

Conclusion

Clutch slipping is a common fault, which makes driving not only uncomfortable, but dangerous too. However, in most cases, any car owner can prevent problems from occurring. You just need to make sure to buy high-quality components and stick to the above recommendations.

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