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Clutch Systems

If you have ever driven a car with manual transmission, or automatic transmission, or for that matter any car, you have used a clutch. Infact many of our daily appliances including electric screwdrivers and chainsaws use clutches.

So what exactly is a clutch??

A clutch is a necessary component of a car because in a car, the engine spins all the time, but the car’s wheels do not. And to stop the car without killing the engine, the wheels need to be disconnected to the engine somehow. The answer to this problem is a ‘Clutch’ which allows us to smoothly engage and disengage a spinning engine with a transmission.

“A clutch is a mechanical device that engages and disengages the power transmission, especially from driving shaft to driven shaft”

Clutches are used whenever the transmission of power or motion must be controlled either in amount or over time (e.g., electric screwdrivers limit how much torque is transmitted through use of a clutch; clutches control the power transmitted from engine to the wheels).

In a modern car with a manual transmission the clutch is operated by the left-most pedal using a hydraulic or cable connection from the pedal to the clutch mechanism. On older cars the clutch might be operated by a mechanical linkage.

Such linkages (either mechanical or through cables) are necessary to eliminate the effect of vibrations and slight engine movement, even though the clutch may physically be located very close to the pedal. With a rigid mechanical linkage, smooth engagement would be near-impossible.

The default state of the clutch is ‘engaged’ – that is the connection between engine and gearbox is always “ON” unless the driver presses the pedal and disengages it. If the engine is running with clutch engaged and the transmission in neutral, the engine spins the input shaft of the transmission, but no power is transmitted to the wheels.

The clutch is located between the engine and the gearbox, as ‘disengaging’ it is required to change gear. Although the gearbox does not stop rotating during a gear change, there is no torque transmitted through it, leading to less friction between gear changes. The output shaft of the gearbox is permanently connected to the final drive, then the wheels, and so both always rotate together, at a fixed speed ratio. With the clutch disengaged, the gearbox input shaft is free to change its speed as the internal ratio is changed. Any resulting difference in speed between the engine and gearbox is evened out as the clutch slips slightly during re-engagement.

Clutches in typical cars are mounted directly to the face of the engine’s flywheel, which provides a convenient large diameter steel disk that can act as a driving plate of the clutch. Both clutch and flywheel are enclosed in a conical bell housing.

 

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Pic credit: repairguide.autozone.com

 REPLACING YOUR CAR’S CLUTCH- DIAGNOSIS

The most common problem with clutches is that the friction material on the disc wears out. The friction material on a clutch disc is very similar to the friction material on the pads of a disc brake or the shoes of a drum brake — after a while, it wears away. When most or all of the friction material is gone, the clutch will start to slip, and eventually it won’t transmit any power from the engine to the wheels.

The clutch only wears while the clutch disc and the flywheel are spinning at different speeds. When they are locked together, the friction material is held tightly against the flywheel, and they spin in sync. It’s only when the clutch disc is slipping against the flywheel that wearing occurs. So, if you are the type of driver who slips the clutch a lot, you’ll wear out your clutch a lot faster.

Sometimes the problem is not with slipping, but with sticking. If your clutch won’t release properly, it will continue to turn the input shaft. This can cause grinding, or completely prevent your car from going into gear. Some common reasons a clutch may stick are:

Broken or stretched clutch cable – The cable needs the right amount of tension to push and pull effectively.

Leaky or defective slave and/or master clutch cylinders – Leaks keep the cylinders from building the necessary amount of pressure.

Air in the hydraulic line – Air affects the hydraulics by taking up space the fluid needs to build pressure.

Misadjusted linkage – When your foot hits the pedal, the linkage transmits the wrong amount of force.

Mismatched clutch components – Not all aftermarket parts work with your clutch.

A “hard” clutch is also a common problem. All clutches require some amount of force to depress fully. If you have to press hard on the pedal, there may be something wrong. Sticking or binding in the pedal linkage, cable, cross shaft, or pivot ball are common causes. Sometimes a blockage or worn seals in the hydraulic system can also cause a hard clutch.

After due diagnosis/consultation with your local mechanic or company authorized workshop, check if your clutch has any of the problems stated above and replace it if necessary.

REPLACING YOUR CAR’S CLUTCH – SELECTING THE RIGHT CLUTCH

Generally speaking, the clutch that came with your car (original equipment), or the one recommended by your car manufacturer is the safest choice. Those clutches are great for day to day driving, and normal driving with high power. It is eminently suitable for high speed freeway drives also.

But for specific purposes like racing, you will have to consider a lot of factors like the weight of your vehicle, the horsepower, torque and output of your engine before choosing a clutch. A street disc is not suitable for racing, as it is made of organic material and thus is intended for smooth engagement and long life. If you choose the wrong clutch, it will quickly slip and shatter. For racing purposes, you can opt for a pucked disc which consists of a variety of different materials such as ceramic and brass. These materials enable the disc, and thus your vehicle, to sustain faster, off-road driving.

 

REPLACING YOUR CAR’S CLUTCH – POST REPLACEMENT CARE

Once you have installed the new clutch within your vehicle, it is fundamental you check the driving conditions of your vehicle. If you experience any issues when getting the vehicle into gear or have slipping issues, do not drive the vehicle until the pedal has been properly adjusted. Otherwise you run the risk of destroying your clutch within a matter of miles. Ensure you double check pedal adjustments whenever you install a new clutch. Always break your clutch in carefully! Don’t try to slip or drag launch your new clutch until you have driven at least a few hundred miles first, to ensure the clutch is fully operational. Also bear in mind that you may void your warranty if you improperly adjust your clutch rod and switches. Contact your local garage or car manufacturer if you are unsure in any way about how you adjust your clutch.

 

 

For more information on the Clutch Systems and Parts for you and your car, get in touch with one of the experts at Spareshub or call us at 020-6920-0102

 

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