How clutches work

MOTORING 

Clutch pedals are found on vehicles that have no automatic transmission.

The automatic transmission system entirely eliminates the need for the mechanical clutch system, but has the reductions or gears that engage and disengage automatically.

Daniel Katumba, a senior mechanic in Rubaga, a Kampala suburb, says the availability of the driver at the driving wheels is a function that results from the operation of the clutch system.

He says without the clutch, there would not be a possibility of the engine idling without affecting the tyres.

Katumba says during driving, a clutch is engaged and disengaged in changing and selecting the necessary reduction in the gear box to combat the power to speed ratio as necessary.

Henry Mivule, another mechanic in Matugga, Wakiso district, says in the commonest type of transmission, which is known as the manual system, the gear reductions are selected by the driver, who engages the gear according to the performance of the vehicle and the type of load it is experiencing.

Mivule says the clutch system is essential in the manual transmission system because it allows gears to be easily slid into selection at a time.

The clutch itself is operated by either a mechanical system (with connecting linkages to the pedal) or by hydraulic means with a master cylinder connected to the pedal that avails the braking force on the wheels.

The clutch suffers defects, such as wear and tear over time, especially if the vehicle is driven in an always jammed environment, where the driver has to keep his foot on the pedal almost all the time.

Besides, an experienced driver can drive with partial pedal depression, allowing the clutch plate to spin at the same time when transmitting the drive.

"One fault, technically often referred to as "soft pedal" or "spongy pedal", is when the clutch pedal is so soft that when the driver depresses it, the clutch is not badly affected, hence making the engagement of gears impossible," Katumba says.

One of the causes of this fault, especially in a hydraulically operated clutch system, is the empty clutch master cylinder.

Mivule says this is because of the leakage in the system, which must be corrected.

The other fault would also be due to the worn-out master cylinder rubbers or seals.

This would need replacement and normally a master cylinder kit would be bought and have the rubbers properly fitted.

Ronald Mayega, another mechanic in Wandegeya, Kampala, says when the master cylinder bore is worn out, the seals, however new, will not affect the braking force because of the side leakage of the fluid.

"When the clutch system has air bubbles inside, the pedal will feel spongy and the remedy is to immediately carry out bleeding of the entire system," he says.

Considering the mechanical pedal operation, if the linkages are broken or are found to be out of adjustment, the pedal will feel spongy and any attempt to have the gears engaged will produce noise and will only enter by force.

By forcing the gears into engagement, the pinions and gearbox can get damaged.

Katumba warns that faults with the clutch system will give the driver a great deal of transmission inconveniences.

How to apply clutches

Asbestos lining is fixed on a plate that is fitted between the gearbox and the engine and sand witched by the pressure plate.

Mayega says disengagement of the clutch usually happens when the driver has passed the clutch pedal down and engagement is when the driver allows the pedal to assume its original position without stepping on the clutch pedal.

He says the pedal has a return spring that is responsible for doing the latter.

Weak or damaged springs will not allow the pedal to return fast, hence making the engagement slow.

The transmission of the turning effect by the clutch is connected to the state and amount of friction.

Any slip or oily stuff on the clutch plate will reduce its transmitting effectiveness, leading the car to develop a clutch slip or spin and as per those faults, excessive wear.

Katumba says when the clutch is not changed when due, the risk of damaging the fly wheel and pressure plate surfaces by the rivets on the clutch linings is greater.

He says if this happens, the driver will have to replace the fl y wheel and pressure plate.

Worn-out clutch plate

A delay in clutch engagement (further pedal return to attain engagement).

Low hill and gradient climbing power.

Weak vehicle take-off from rest.

There are other clutch faults and defects, such as a buckled or bent and distorted clutch plate.

Clutch plate seizure on the gearbox input shaft and broken release levers.

An occurrence of fierce and jumpy clutch engagement, technically known as clutch judder.

This is when, at the release of the clutch pedal, the vehicle vibrates. This is mainly caused by worn-out linings and protruding rivets.

Distorted or bent clutch plate.

Loose engine or gearbox mountings or slack tie rods on the steering system.