3. FUCTION OF A CLUTCH AND BRAKES
The function of a clutch is to engage or disengage a machine (or machine
component) without starting or stopping the driver. Different types of clutches can
also provide the following:
• a. Slower, smooth engagement and disengagement under full speed.
• b. Quick engagement and disengagement.
• c. Overload protection by limiting the maximum torque loads.
• d. Prevention of accidental machine reversal.
Brakes are actually clutches with one side locked down so when the
clutch/brake engages the rotating shaft stops.
8. MECHANICAL CLUTCHES
i. Friction Clutches
• Widely used in industry (i.e. automotive industry).
• Can be actuated or operated manually, pneumatically or hydraulically.
• Use a lined metal of fibrous metal mounted between two steel plates as a means of transferring
motion between two mechanical components.
• Transferring of motion occur when the separate plates are bought into contact with each other.
• The travel of the friction plates is very small compared to the jaw clutches.
• The driven portion of a friction clutch is frequently supported by bearings on the driving hub.
9. MECHANICAL CLUTCHES
ii. Jaw Clutches
• Usually used on slow speed applications.
• Motion for engaging and disengaging the clutch is accomplished with a shifting arm.
• The shifting arm are usually has the fulcrum or pivot point located at one end of the arm with the operating handle
located at the other end.
iii. Centrifugal Clutches
• Friction type centrifugal clutches are commonly found in applications where it is desirable to have either no load starting or
protection against overload.
• Can also function as couplings or can be mounted directly to V-belt.
• In operation, centrifugal clutches start from a disengaged or at rest position.
• Centrifugal clutches become positively engaged at no time during operation.
10. MECHANICAL CLUTCHES
iv. Overrunning Clutches
• Also known as one-way clutches.
• Frequently used on machine where the driving motor or media requires protection.
• Prevent over speeding of the drive by allowing free rotation of the drive component.
• Designed to permit rotation of the driving force in the forward direction only.
• To accomplish this overrunning action, two common type of mechanism are used rollers and sprags.
• Rollers running on flat surface inside round housing while sprags positioned between two circular surfaces.
Sprags are irregular or can shaped pieces.
• During operation, sprags are wedged between the inner and outer hubs.
11. MECHANICAL CLUTCHES
v. Torque Limiting Clutches
• Used on any number of different pieces of equipment or also used with roller chain type
coupling.
• The driven half of the clutch is always engaged during startup and only slip when overloaded.
vi. Tooth Clutches
• Used pneumatic of hydraulic actuating cylinder to operate.
• The mating surface of a tooth clutch is constructed with notches or serrations.
• In operation, the notched surfaces contact each other motion is transmitted from the driving to
the driven halves of the clutch.
12. HYDRAULIC CLUTCHES
i. Fluid Clutches
• Widely used in industry because of their ability to start under heavy loads and
absorb shock loads.
• Also used to provide a smooth flow of power to the driven side of a machine. (Also
known as fluid coupling).
• The driven half of a fluid coupling is actuated by the hydraulic fluid.
• The driving half (pump/impeller) and driven half (turbine) will rotate at the same
speed during operation.
13. ELECTRIC CLUTCHES
• Used where intermittent motion is required especially to start and stop the drive motor on short time cycles.
• A magnet or coil is mounted on a driven component or machine while an armature plate is mounted on the
driving motor or shaft.
• When the two parts are de-energized, no contact or action takes place between them, even though the motor
the motor may be
• running.
• When an electric current is introduced into the magnet or coil, a magnetic field is set up causing the armature
and the coil to draw together.
• This action then couples the two halves electrically and physically causing them to rotate as one piece.
15. DISSEMBLE CLUTCH AND BRAKE
i. Remove the engine from the car.
ii. If the old pressure plate is to be reused, scribe or paint alignment marks on the pressure plate and the flywheel to ensure proper
realignment of the pressure plate during reassembly.
iii. Hold the pressure plate securely and completely, then loosen the pressure plate-to-flywheel bolts by turning each bolt only a little at a time.
Work in a criss-cross pattern until all spring pressure is relieved. Then remove the bolts, followed by the pressure plate and the clutch disc.
iv. Clean the friction surface on the flywheel and inspect it for wear, cracks, heat checking, grooves, and other obvious defects. Alternating
brigt and dull areas indicate a warped plate. A machine shop can machine the surface flat and smooth (highly recommended, regardless of
the surface appearance). Light glazing can be removed with medium grit emery cloth.
v. Inspect the diaphragm spring fingers for excessive wear and make sure they are not distorted.
vi. Shake the pressure plate assembly and verify that the diaphragm spring, which should be under tension, does not rattle. If the pressure
plate is defective in any way, replace it.
vii. If you will be reinstalling the engine you removed, clean the flywheel and pressure plate friction surfaces with lacquer thinner or acetone.
viii. Inspect the clutch release (throw-out) bearing. If it feels gritty when you turn it, or if it has been making noise, replace it. Never wash the
bearing in solvent since this will remove the factory-installed lubricant. If the bearing is unserviceable, replace per the procedure.
16. DISSEMBLE CLUTCH AND BRAKE
ix. Inspect the lining on the clutch disk for wear. There should be at least 2mm of friction
material remaining above the rivet heads.
x. Check the clutch disk for loose rivets, distortion, cracks, broken springs and other obvious
damage.
xi. Carefully inspect the splines inside the hub of the clutch disk and the splines on the
transmission input shaft. They must not be broken or distorted. Lubricate the splines in
the disk hub and the splines on the input shaft with graphite or molybdenum disulfide
powder (Rob's last replacement clutch plate came with a tiny tube of special "spline"
grease to be smeared sparingly on the splines).
xii. Verify that the clutch disk slides freely on the drive shaft splines without excessive radial
play. If the clutch disk is in any way unserviceable, replace it.
18. REASSEMBLE
i. Install the flywheel, if removed.
ii. Clean the flywheel and pressure plate friction surfaces with lacquer thinner or acetone.
iii. Position the clutch disk and pressure plate against the flywheel with the clutch held in place with an alignment tool (the
best alignment tool is an old input shaft, or there is a commerciallyavailable inexpensive one made of plastic).
iv. Make SURE the clutch disk is installed properly (most replacement clutch plates will be marked "flywheel side" or
something similar. If not marked, install the clutch disk with the damper springs towards the transaxle.
v. If you're reusing the old pressure plate, make sure the marks you made on the pressure plate and the flywheel are
matched up.
vi. Install a clutch alignment tool into the center of the clutch disc you intend to use. With the clutch disc on the alignment
tool, install the tool into the end of the crankshaft. Make sure that the alignment tool extends through the splined hub
and into the needle bearing in the gland nut. Wiggle the tool up-down and/or side-to-side as needed to bottom the tool
into the gland nut.
19. REASSEMBLE
vii. Make sure that the clutch disc is against the flywheel, then install the pressure plate.
viii. Loosely start the six mounting bolts in the flywheel. Tighten them "crosswise", back and forth across the plate to
prevent distorting the cover. After all the bolts are snug, torque them first to about 10 ft-lbs and finally to 18 ft-lbs.
ix. Center the clutch disk by ensuring the alignment tool extends through the splined hub and into the needle bearing in the
gland nut. Wiggle the tool up-down and/or side-to-side as needed to bottom the tool into the gland nut.
x. Loosely install all of the mounting bolts. Tighten them "crosswise", back and forth across the plate to prevent distorting
the cover. After all the bolts are snug, torque them first to about 10 ft-lbs and finally to 18 ft-lbs.
xi. Install the clutch release bearing if removed. Be sure to lubricate the bore of the release bearing and the outer surface of
the central guide sleeve with high-temperature grease, and apply multi-purpose grease to the contact areas of the forks
on the release shaft.
xii. Reinstall the engine in accordance with our Engine Installation Procedure.
xiii. Adjust the clutch pedal free play in accordance with our Clutch Cable Adjustment Procedure.
21. CHECK LIST CLUTCHES AND BRAKES MAINTENANCE, SYMPTOMS
AND RECORD OBSERVATIONS
FOR PREVENTIVE MAINTENANCE
i. Improper adjustment of clutch or brake: The clutch or brake may not be fully engaging. Follow the manufacturer’s adjustment procedures.
ii. Oil or contaminant on friction surfaces: Clean or replace the surfaces.
iii. Worn out friction components: Check the components to see if they are within tolerances. Replace them if necessary.
iv. Worn linkage or parts used in engaging clutch or brake: Sometimes adjustment is adequate to compensate for wear. Check for obstruction
and corrosion on moving parts. Clean or replace the parts as necessary. Check lubrication, and relubricate if required.
v. Too much torque: This may be because an increased load exceeds design capacity or because of poor initial selection of a clutch or brake.
Check the machine to determine if the increased load is temporary or permanent. Repairing or servicing a machine may reduce torque to
acceptable levels. If not, the clutch or brake should be replaced with one designed for the increased torque loads required.
vi. High-frequency cycling or high-inertia loads: Generally, these cases of excessive heat can be solved only by changing to a clutch or brake
with greater heat-dissipation ability. Sometimes a fan or blower may be used to increase air flow, thus cooling equipment. Shortening the
slipping time during start-up can also reduce heat. Less slippage means less heat, but make sure that engagement is not so sudden that
severe shock loads are created in the machine. Engaging clutches under the lightest possible startup loads is always recommended.
22. With any type of clutch or brake, the following
are generally recommended:
i. The clutch or brake should always be the correct size for the application.
ii. Heat dissipation should always be adequate to ensure long life and low
maintenance.
iii. Lubrication, if required, should be done on a periodic, regular schedule.
iv. Components should be checked regularly for adjustment and wear.
v. Clutches and brakes should be kept clean and free from debris whenever
possible.
