Clutch Flashcards
Where is the clutch assembly found?
Inside the bell housing
What is the purpose of a clutch?
To assist in transmitting the drive of the engine to the road wheels smoothly
What are the benefits of using a clutch?
- Disconnects power produced by the engine from the gearbox
- Progressively connects power to the gearbox, allowing a smooth take up of drive
What are the different types of clutch?
- Dog clutch
- Friction cone clutch
- Basic friction plate clutch
What is a key feature of a dog clutch?
Two mated castellated faces
What is the major disadvantage of a dog clutch?
It is difficult to connect the two castellated faces when the revolutions are high
What is a major disadvantage of a friction cone clutch?
Heat from friction can cause expansion of the male end inside the female end
What is the most common type of main clutch in a vehicle?
Friction plate clutch
What are the parts of a clutch assembly?
- Flywheel
- Driven plate
- Pressure plate
- Release bearing
- Release arm
What are the functions of a flywheel?
- Absorb and release kinetic energy during idle strokes
- Reduce vibration
- Transmits starter motor power
- Mounting surface for clutch assembly using dowels
What is the purpose of a spigot bearing?
- Supports the end of the gearbox input shaft
- Allows a differential speed between the crankshaft and gearbox input shaft
- Allows the input shaft to slow down when the clutch is operated whilst the engines running
What types of spigot bearing are there?
- Ball type bearing
- Phosphor bronze type
What type of fit are spigot bearings?
Interference fit
Why are ball type spigot bearings sealed for life?
To prevent grease escaping and frequent difficult maintenance
What is the driven plate also known as?
Friction plate or centre plate
What faults could occur if a plan steel plate with friction material attached to each side was used?
- Buckling of the plate due to hear which could cause drag
(Drag is the plate rubbing against flywheel/pressure plate even though the clutch pedal is fully down) - Small movement of the pedal between engagement and release of the clutch can cause erratic/harsh drive take up
Why must you wear PPE when dealing with friction plates?
They may contain asbestos
What feature is used on a friction plate to prevent buckling?
Slots to allow a flexing action
What is the purpose of alternately fixed riveting on a friction plate?
To give a wavy profile called ‘borglite crimping’
What is the purpose of borglite crimping?
Helps the lining spring apart when the clutch is disengaged to prevent clutch drag
What effects does increasing the axial compression on a driven plate have?
- Spreads engagement over a greater range of pedal movement, allowing a smoother engagement of drive
- Increases airflow between segments and friction surfaces, enhancing heat dissipation
What are the purpose of large slots in the inner hub of a clutch?
To accommodate damper springs
What are the purpose of damper springs?
- Transmit drive
- Absorb torsional shocks during drive engagement, from engine vibrations and during overrun
What is overrun?
When the wheels are driving the gearbox, rather than the gearbox driving the wheels
What are the functions of the pressure plate?
- To provide a flat face that mates with the friction plate
- To provide a clamping force on to the friction plate to transmit drive
What are the two basic designs of pressure plate assemblies?
- Diaphragm spring
- Multi-coil spring
What are advantages of a diaphragm spring?
- Compact and lightweight
- Less moving parts
- Suitable for high engine speeds because:
Not affected by centrifugal force
No vibrations due to spring imbalance - Lower pedal force is required to release clamping pressure
- Clamping force does not reduce as friction linings wear
What are the purpose of drive straps?
To transmit drive from the cover to the pressure plate
What shapes do the diaphragm spring alter from during operation?
From convex to concave
What is the purpose of a fulcrum ring?
To act as a lever to cause the diaphragm spring to change shape as oppose to move
What are drive straps made of?
Spring steel
What are disadvantages of a multi-coil spring?
- Bulky and expensive to manufacture
- Prone to centrifugal effects
- Large pedal force required
- Clamping force decreases as friction linings wear
What are the parts of a multi coil spring pressure plate?
- Pressure plate casting
- Pressed steel cover
- Coil springs (avg 16)
- Release lever (3 or more)
- Eye bolt assembly (each one has 3 components)
- Anti-rattle springs (same amount as levers)
- Thrust ring (if fitted)
What is the purpose of a knife edge in a release lever?
- Acts as a double pivot point between the release lever and the pressure plate
- Ensures the pressure plate moves squarely in relation to the centre plate
What are the purpose of the anti rattle springs?
Springs are placed to ensure the release lever is held in the correct position and reduces unwanted noise
What creates the clamping force in a multi-coil spring plate?
The springs
What 3 parts make up the release lever assembly?
- Eye bolt
- Release lever (toggle lever)
- Knife edge
What determines how much torque can be transmitted by a plate-type clutch?
- Size of the clutch (radius)
- Pressure applied by the pressure plate
- Area of contact for the centre plate
What are the 2 main types of multi plate clutch?
- Dry
- Wet
What components make up a wet multi plate clutch?
- Clutch cover
- Inner hub (inc. primary shaft)
- Outer plates
- Inner plates
- Withdrawal sleeve
- Thrust springs
What two designs of wet clutch cover are there?
One or two piece pressed steel
What feature on a wet clutch inner plate allows for easier separation?
They are slightly dished
What replaces a release bearing in a wet clutch?
A withdrawal sleeve
Can you service a release bearing?
No
What two types of release bearing are there?
- Enclosed ball race bearing
- Solid bonded carbon pad
What is a release arm also known as?
Clutch fork
What two types of material are clutch forks made of and why?
- Pressed steel: Light to medium duty
- Drop forged steel: Heavy duty
What is FPM?
Free pedal movement, the movement in the clutch pedal before drive is disengaged
How do we adjust free pedal movement?
At the pushrod
What are the two main reasons for FPM?
- To keep release bearing clear of the pressure plate to prevent premature wear
- To ensure full spring pressure acts on the pressure plate when drive is engaged
What 2 methods of clutch operating mechanisms are there?
- Mechanical (cable or rod)
- Hydraulic
What type of automatic cable adjustment is there?
Quadrant and pawl
How is assistance provided to operate the clutch in heavy vehicles?
Clutch (air) servo
In a clutch air servo, what component seals the air inlet when the clutch pedal is released?
Reaction Plunger
What component seals the exhaust valve when the clutch pedal is pressed?
Reaction member
What are the 5 main faults that can cause in the clutch assembly?
- Slip
- Drag
- Judder
- Fierceness
- Bearing noise
What are the symptoms of clutch slip?
- Rev increase without vehicle speed increasing
- Smell of burning friction material
- In severe cases the vehicle will not drive up steep hills
What can cause clutch slip?
- Insufficient free pedal movement
- Worn clutch driven plate facings
- Partial seizure of pedal linkage/hydraulic cylinder
- Defective/partially seized pressure plate
- Oil contaminated clutch facings
- Fouling of the pedal preventing full return
What are the symptoms of clutch drag?
- Difficulty in engaging 1st or reverse gear from neutral
- Vehicle jolts when changing gear with vehicle in motion
- May continue to move when the clutch pedal is fully depressed
What are possible causes of clutch drag?
- Excessive FPM (incorrect adjustment or lack of hydraulic fluid or air in the system)
- Fouling/wear of linkage preventing pedal being fully depressed
- Oil-contaminated facings causing one to stick to a driving surface
- Defective driven plate or seizure on splines
- Misalignment of friction faces
- Partially seized or collapsed spigot bearing
What are the symptoms of clutch judder?
A severe, low frequency vibration wen the clutch is released while vehicle is moving from stationary
What are the possible causes of clutch judder?
- Jerky pedal - Sticking cable or pivot point
- Excessive engine movement during take up of drive because of defective: Tie rod, drive line, suspension
- Oil-contaminated facings
- Defective pressure plate
- Misalignment of friction faces
- Defective driven plate
- Defective diaphragm spring causing an imbalance
What is the symptoms of clutch fierceness?
Sudden engagement of the clutch, even though its being gradually released
What are possible causes of clutch fierceness?
Any defect that allows clutch take-up to be faster than the movement of the pedal, including: Partial seizure of the pedal linkage, contamination of hydraulic fluid
- Driven/centre plate contamination
- Misalignment of friction faces
What are the symptoms of bearing noise?
- A rumbling or squealing when the clutch is pressed
- Noise disappears when clutch is released
What are the possible causes of bearing noise?
- Defect in the release bearing, including: Dry bearing, seized bearing, fair wear and tear
- Excessive bearing wear caused by incorrect clutch FPM
- Partially seized linkage
What type of clutch do automatic gearboxes use?
Fluid clutches
What are the two main types of fluid clutch assembly?
- Fluid flywheel
- Torque converter
What is a disadvantage of a fluid flywheel?
Slip cannot be completely eliminated
What is the purpose of the stator in a torque converter?
To increase the speed of the turbine
What are the 3 main differences between a torque converter and a fluid flywheel?
- Contains a stator
- Vanes are angled
- 2 flow control rings
Where is the stator in a torque converter?
Mounted on a one way clutch
What is the stator also known as in a torque converter?
A reaction member
What is the purpose of the lock up clutch?
To keep the impeller and the turbine together to spin at the same speeds
What type of one way clutch is in a torque converter?
Sprag type
What is maintenance of a torque converter limited to?
- Oil change (gearbox oil)
- Replacement of oil seals (on gearbox)
- Check with associated publication (AESP or AP) for any further maintenance
