Clutches
Objectives • Describe the various clutch components and their functions. • Name and explain the advantages of the different types of pressure plate assemblies. • List the safety precautions that should be followed during clutch servicing. continued…
Objectives • Explain how to perform basic clutch maintenance. • Name the six most common problems that occur with clutches. • Explain the basics of servicing a clutch assembly.
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Drive Trains Rear-Wheel Drive Vehicle
Front-Wheel Drive Vehicle
Automotive Clutch • Used to connect and disconnect the engine and manual transmission or transaxle • Allows the driver driver to control control power flow between the engine and transmission or transaxle
• Vehicles with manual transmissions require a clutch • Power flow from one unit to another can be controlled with a drive disc and a driven disc
Clutch Theory Clutch is disengaged
Clutch is engaged
Introduction Clutches In order to change gear, the drive between the engine and the gearbox must be temporarily disconnected. The vehicle clutch enables the driver to do this.
A clutch is a component that is designed to connect connect together two rotating shafts. Clutches can be classified as one of two types - positive engagement (dog clutch) or gradual engagement (friction clutch). Positive engagement clutches normally use teeth in order to provide a positive connection, whereas gradual engagement clutches use friction
The clutch is situated between the engine and the transmission gearbox. In this example depressing the clutch pedal will engage and disengage the engine from the transmission. The clutch is designed to gradually and smoothly transmit power from the engine to the transmission to enable a vehicle to start off under full control. Note: The ability of a clutch to transmit torque (clutch capacity) is normally between 1.2 and 1.4 times the maximum torque of the engine. Commercial vehicles usually have a capacity between 1.5 and 2.5. If the clutch is too light, slipping will take place and lead to premature failure. Too large a clutch will will tend to cause the engine to stall and is inefficient
Requirements of a vehicle clutch • • • • • •
it must connect power smoothly it must transmit power without slipping it must disengage quickly and smoothly it must have good heat radiating properties it must be well balanced it must be trouble free and have a long service life • it must must be be easy to inspect, inspect, adjust and repair.
Basic Clutch Parts The clutch assembly consists of two major items, cover assembly (containing pressure plate and spring) and the clutch friction plate or disc which is trapped between the engine fly wheel and the cover assembly
Simplified Clutch
Clutch Components
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Clutch Action (Disengaged) • When driver presses the clutch pedal, clutch release mechanism pulls or pushes on the clutch fork • Fork moves the release bearing into the center of the pressure plate • Pressure plate face pulls away from the clutch disc • Clutch disc and transmission input do not turn
Clutch Action (Disengaged)
Clutch Action (Engaged) • When driver releases the clutch pedal, spring pressure inside the pressure plate pushes forward on the clutch disc • This locks the flywheel, disc, pressure plate, and transmission input together • Engine rotates the transmission input
Clutch Action (Engaged)
Coil spring type The cover assembly is bolted to the flywheel and rotates at engine speed. The friction disc is splined to the gearbox input shaft. Trapped between between the pressure plate and flywheel flywheel by spring pressure, the disc will transmit power to the transmission. Depressing the clutch pedal will cause the lever to move the release bearing and reli eve the pressure exerted by the spring on the disc. This will cause the disc to spin freely between between the flywheel and the pressure pressure plate. Power cannot therefore therefore be transmitted to the transmission
Diaphragm spring type There are two main types of clutch cover assembly. assembly. The type illustrated uses coil springs to trap the friction disc between the pressure plate and the flywheel. The clutch cover uses a diaphragm spring
• Components: – pilot bearing – flywheel – clutch disc – pressure plate – release bearing – clutch housing (bell housing) – clutch release mechanisms – clutch start switch
Clutch Components • Clutch housing – Connects engine and transmission and houses the clutch assembly.
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Clutch (Bell) Housing • Bolts to the rear of the engine • Encloses the clutch assembly • Made of aluminum, magnesium, or cast iron • Transmission bolts bolts to the back of the clutch housing
Clutch Components • Flywheel – Acts – Acts as balancer for the engine. – Adds – Adds inertia to the rotating crankshaft. – Provides a surface for the clutch to contact. Some flywheel have Ring gear for starter engagement Some vehicles have dual mass flywheel
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Flywheel • A mounting place place for the clutch • The pressure plate bolts to the flywheel face • Flywheel face is precision machined to a smooth surface, where it contacts the clutch disc • Normally made of iron for good wear and heat dissipation
Clutch Components • Clutch (input) shaft – Projects from the front of the transmission. – Usually has a pilot that rides in a bearing or bushing in the end of the crankshaft. – The clutch disc is splined to the clutch shaft. – When engaged, the clutch disc drives the input shaft. continued…
Clutch Disc • Consists of a splined metal hub and a round metal plate covered with friction material (lining) • “Spl “Splin ined ed”” to the the tran transm smis issi sion on inp input shaf shaftt • Disc is free to slide back and forth on the shaft
Clutch Components • Clutch disc – Is covered with friction material. – Transmits power from the engine crankshaft to the transmission input shaft. – Torsional coil springs or rubber grommets gr ommets allow the disc to rotate slightly in relation to the pressure plate while they absorb the torque forces. continued…
Clutch Components Clutch disc
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Clutch Disc The central hub is splined to fit on the gearbox input shaft and is free to rotate a limited distance in relation to the friction faces. This movement is governed by torsion dampers made usually from coil springs or rubber inserts and reduces initial shock at power take up.
There is a tendency for the disc to stick to the flywheel or pressure plate when released in much the same way that two sheets of glass are hard to separate due to air pressure. Grooves in the friction faces help air to enter the t he gap forming when the pressure plate moves away from the disc.
Clutch Components • Clutch disc (co (cont’) – The clutch facings are riveted to wave springs, or cushioning springs, which cause the contact pressure on the facings to rise gradually when the clutch is engaged. – These springs eliminate chatter by dampening the clutch engagement.
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Clutch Disc Torsion Springs • Help absorb some of the vibration and shock produced by clutch engagement • Small coil springs located between the clutch disc hub and the friction disc
Clutch Disc Facing Springs • Flat, Flat, met metal al spri spring ngs s locat located ed under under the disc’s disc’s friction material • Springs have a light wave (curve) – allow the friction material to flex inward slightly during clutch engagement – flexing smoothes engagement
Clutch Disc Friction Material •
Made of heat-resistant substances
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Grooves cut in the material aid cooling
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Rivets are commonly used to bond the friction material to both sides of the metal body of the disc
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Leather ,cork,fabric,Asbestos – Reybestos and ferodo > most suitable, Widely used – Non asbestos clutch • Glass fibre mixed with special rubber • Kavalar with brass wire • Sintered metal friction
Pressure Plate • Spring loaded device • Locks or unlocks the clutch disc and the flywheel • Clutch disc fits between the flywheel and pressure plate • Two basic types: – coil spring – diaphragm spring
Clutch Components Diaphragm Spring
Coil Spring
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Components • Small coil springs – clamp clutch disc between face and flywheel
• Face – large ring that contacts the clutch disc
• Release levers – allow the release bearing to move the face – hinged inside the pressure plate
Diaphragm Spring Pressure Plate • Uses a single diaphragm spring instead of several coil springs • Diaphragm spring is a large, round disc of spring steel which rides on a pivot ring part way in from the outer edge • Pushing in on the center of the spring bends the outer edge away from the engine, releasing the clutch disc
Diaphragm Spring Pressure Plate
Clutch Components • Release bearing – Is operated by the clutch linkage. – Presses against the pressure plate to release the clutch.
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Release Bearing • Usually a ball bearing and collar assembly that reduces friction between the pressure plate levers and the clutch fork • A few imported vehicles use a graphite graphite bearing – ring shaped block of graphite presses on a smooth, flat plate on the clutch release levers
Clutch Components • Pilot bearings – The purpose of the pilot bushing or bearing is to support the outer end of the transmission’s input shaft. – Allows – Allows the input shaft to rotate in the crankshaft. continued…
Pilot Bearing • Made of a solid bronze bushing, roller or ball bearing • Prevents the transmission shaft and clutch disc from wobbling when the clutch is released
Clutch Linkage • Clutch linkage transfers the clutch pedal movement to the release bearing. – Mechanical clutch linkage uses shafts, levers, or a cable. continued…
Clutch Cable Mechanism
Clutch Cable Mechanism • Uses a steel cable inside a flexible housing to transfer pedal movement to the clutch fork • One end usually has a threaded sleeve for clutch adjustment
Clutch Linkage Mechanism
Clutch Linkage Mechanism • Uses levers and rods to transfer motion from the clutch pedal to the clutch fork • A bellcrank may be used to reverse the movement of the clutch pedal • A release rod transfers motion to the fork and allows adjustment
Clutch Linkage Hydraulic clutch linkage consists of a master cylinder, hydraulic tubing, and a slave cylinder.
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Hydraulic Clutch Release Mechanism • Uses a simple hydraulic circuit to transfer clutch pedal action to the clutch fork • Components: – clutch cylinder – hydraulic line – slave cylinder
Clutch Cylinder • Produces hydraulic pressure for the system • Mounted to the firewall or cowl • Push rod links the clutch pedal and the cylinder piston • Most systems use brake fluid
Clutch Cylinder
Slave Cylinder
Uses hydraulic pressure to cause clutch fork movement
Multiplate Clutch Assembly Drum Piston Seals Return Springs Snap Ring Lined Discs
A typical clutch assembly contains the apply piston, piston return springs, and the clutch plates.
Pressure Plate Unlined Plates
Common Clutch Problems • Clutch slippage – Definition: With the clutch engaged, engine speed increases but vehicle speed does not. – Before disassembly: • Check linkage. • Check for worn or binding parts. • Check engine mounts.
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Common Clutch Problems • Other causes for clutch slippage – Oil-soaked or worn disc facings – Warped flywheel or pressure plate – Weak pressure plate springs – Contact between the release bearing and the fingers of the pressure plate
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Common Clutch Problems • Clutch chatter – Definition: Shaking or shuddering when clutch is engaged. – Before Disassembly: • Check engine mounts. • Check for leaks from rear main seal, transmission input shaft seal, and clutch slave cylinder. continued…
Common Clutch Problems • Clutch noises – These noises are usually caused by bad bearings or bushings. – To diagnose, determine whether the noise changes with the clutch engaged or disengaged.
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Common Clutch Problems • Causes for damaged release bearings – Misalignment – Overheating – Slippage – Component damage
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Common Clutch Problems • Clutch vibrations – Are – Are usually caused by worn worn engine mounts, loose bolts, excessive flywheel runout, or flywheel and/or pressure plate assembly imbalance.
• Dragging clutch – Is usually caused by linkage problems, incorrect pedal adjustments, or defective clutch assembly. continued…
Common Clutch Problems • Pulsating clutch pedal – Is usually caused by broken or bent release levers, misaligned bell housing, or warped pressure plate, flywheel, or clutch disc.
• Binding clutch – Is usually caused by binding linkage or cables, defective clutch assembly, or improper installation.
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Flywheel service • Visually inspect for hot spots, grooves, scoring and cracks • Check with dial indicator for run out and crank end play • Most flywheels can (should) be resurfaced – Must remove dowel pins
• Inspect ring gear
Clutch Service Checks Measuring flywheel runout and Crankshaft endplay
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Clutch Service Checks Measuring clutch housing face runout
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Hydraulic Clutch Problems • Soft clutch pedal or excessive pedal travel – Is usually caused by low fluid level. – May be caused by a faulty master or slave cylinder.
• Hard pedal – Is commonly caused by binding linkage or swollen cups in the master or slave cylinder.
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Clutch disc service • Inspect for wear similar to brake pads • Common to have loose or broken springs • Common failure due to oil contamination – Must find cause BEFORE repair
Clutch disc service • Clutch disc will normally have a flywheel side • Disc must be centered with clutch alignment tool before pressure plate bolted down • Make sure new disc fits on input shaft of the transmission before you install it
Pressure plate service • Mark relation to flywheel if reused • Remove bolts slowly in criss-cross pattern • Inspect fingers for parallelism, cracking or uneven wear • Inspect friction surface for hot spots, cracks etc and with straight edge for warpage • Must be torqued to specs and in sequence • Uses hard bolts
Release bearing service • Very common failure - isolated by lightly applying clutch and listening • Inspect for looseness or roughness • Most are sealed but some were lubeable • Clutch fork must be lubed at pivot point and bearing contact points • Bearing retainer and input shaft should be lubed • Clutch fork must be secured at the pivot point
Pilot servicing • Should always be changed with clutch • Can be isolated by applying clutch in gear • Special pullers may be used for removal – Can be removed with grease
• Should be lightly lubed on installation
