Outline of Automotive Clutch


The clutch is located between the engine and the manual transaxle (manual transmission) and connects and disconnects the engine power by operating the clutch pedal. Thus, the clutch can gradually transmit power from the engine to the drive wheels in order to start the automobile smoothly, and smoothly change the transmission gears according to the conditions under which the vehicle is traveling.

Requirements of the clutch

(1) It must engage the transmission and the engine smoothly.

(2) Once it engages the transmission, it must transmit power entirely without slipping.

(3) It must disengage the transmission quickly and with precision.

The clutch consists of a portion that operates mechanically to transmit power, and a portion that utilizes hydraulic pressure to transmit power.

Cable type clutch

There are also cable type clutches that connect the clutch pedal and the release fork by cable.

Clutch Pedal

The clutch pedal generates hydraulic pressure from the master cylinder with the force from depressing the pedal.

This hydraulic pressure is applied to the release cylinder and the clutch is finally engaged and disengaged.

Clutch pedal freeplay

The clutch pedal freeplay is the distance that the pedal can be depressed until the release bearing presses against the diaphragm spring. As the clutch disc wears, the freeplay is reduced. If the disc wears further and there is no more freeplay, this causes the clutch to slip. Therefore, it is necessary to adjust the length of the release cylinder push rod and hold the freeplay constant. Therefore, it is necessary to adjust the length of the release cylinder push rod and hold the freeplay constant. In current models, self-adjusting release cylinders are used, so the clutch pedal freeplay does not change. The clutch pedal height is adjusted with the pedal stopper bolt and the pedal freeplay is adjusted with the push rod length.

Turn-over Type Clutch Pedal

Turn-over type clutch pedals are clutch pedals that utilize spring force to reduce the operating force.

When the pedal is depressed and goes beyond a certain position, the spring force operating direction changes and is added with the force to be depressed. The spring is installed between the

clutch pedal and pedal support and force works on the spring to keep it constantly

extended. There are various types of turn-over type clutch pedals with different constructions.

TFT (Toyota Free-Tronic)

The TFT (Toyota Free-Tronic) has no clutch pedal and consists of the parts in the diagram on the left in addition to the conventional clutch construction. By performing the shift operation, the TFT ECU controls the hydraulic actuator based on the signals from the sensors and switches to send hydraulic pressure to the release cylinder and automatically operate the clutch. Since it is equipped with protection control, it warns the driver with a buzzer and the indicator

(1) Clutch pedal depressed

The piston is moved to the left via the push rod when the clutch pedal is depressed. The brake fluid in the cylinder flows through the inlet valve to the reservoir and at the same time to the release cylinder.

When the piston moves further to the left, the connecting rod is separated from the spring retainer, and the inlet valve closes the passage into the reservoir by the conical spring, as a result, a build up of a hydraulic pressure in chamber A occurs which is transmitted to the release cylinder piston.

(2) Clutch pedal released

When the clutch pedal is released, the piston is pushed back to the right by the compression spring and hydraulic pressure decreases. As the piston returns completely, the connecting rod is pulled to the right by the spring retainer. The inlet valve thus opens the passage to the reservoir and chamber A and B are connected.


If air is mixed into the fluid line, air is pressurized and sufficient amount of oil pressure is not generated. Then, it causes poor clutching or the gears unable to shift.

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