Clutch and torque converters (week 2)

Function of a clutch

Connects and disconnects engine power to the drivetrain; allows smooth gear changes and stopping without stalling

Clutch engaged (pedal released)

Pressure plate clamps disc to flywheel; power flows to transmission

Clutch disengaged (pedal pressed)

Pressure plate moves away; no power transfer

Push-type clutch

Bearing moves toward engine; external adjustment; no clutch brake; higher pedal effort

Pull-type clutch

Bearing moves away from engine; internal adjustment; works with clutch brake; higher torque capacity

Flywheel

Connected to engine; provides rotating surface for clutch

Clutch disc

Transfers torque between flywheel and transmission

Pressure plate

Applies clamping force to clutch disc

Release bearing

Engages and disengages the clutch

Clutch hub

Connects disc to transmission input shaft

Rigid disc

No springs; cannot absorb shock; risk of damage

Dampened disc

Has springs; absorbs vibration; protects drivetrain

Organic friction material

Smooth engagement; lower heat resistance; light-duty use

Ceramic friction material

High heat resistance; aggressive engagement; heavy-duty use

Coil springs

Provide clamp force in clutch

Angle springs

Reduce pedal effort; maintain constant load

Diaphragm springs

Low pedal effort; consistent pressure

Manual clutch adjustment

Uses adjusting ring to compensate for wear

Self-adjusting clutch

Automatically adjusts using internal mechanism

Clutch capacity factors

Size, number of discs, material, and clamp load

Mechanical linkage

Rods or cables; requires adjustment

Hydraulic linkage

Uses fluid pressure; self-compensating

Boosted hydraulic linkage

Air-assisted; reduces pedal effort

Concentric slave cylinder

Mounted on input shaft; harder to service

Clutch brake

Stops transmission input shaft for shifting into gear

Clutch brake use

Used only for first gear and reverse

Release travel

~0.500-0.560 inches

Free play

~1/8 inch

Clutch brake clearance

~1/2-9/16 inch

Single plate clutch

Simpler; lower torque capacity

Two plate clutch

Higher torque capacity; more complex

Burnt clutch disc

Caused by slipping or riding the clutch

Oil-soaked disc

Caused by engine or transmission leaks

Broken springs

Caused by shock loads or vibration

Release bearing failure

Caused by poor lubrication or riding pedal

Warped disc

Caused by improper installation

Flywheel runout spec

≤ .008 inches

Pilot bearing runout spec

≤ .005 inches

Clamp load

Force holding clutch disc against flywheel

Damper

Absorbs torsional vibration

Release load

Force required to disengage clutch

Plate departure

Movement of plate when clutch disengages

Clutch brake squeeze

Pedal travel needed to engage clutch brake

Hydrostatic system

High pressure, low velocity fluid systems (ex: brakes, cylinders)

Hydrodynamic system

Low pressure, high velocity fluid systems (ex: torque converter)

Fluid coupling principle

Moving fluid transfers energy between components

Curved blades advantage

Smoother flow and greater force

Torque converter

Fluid coupling that transmits and multiplies torque

Impeller (pump)

Driven by engine; moves fluid outward

Turbine

Driven by fluid; turns transmission input shaft

Stator

Redirects fluid to increase torque

Lockup clutch

Creates direct mechanical connection; eliminates slip

Flexplate

Connects torque converter to crankshaft

Torque converter basic operation

Impeller moves fluid → turbine spins → stator redirects flow

Vortex flow

Fluid moves opposite rotation; increases torque

Rotary flow

Fluid moves with rotation; increases efficiency

Torque multiplication phase

Impeller fast, turbine slow; stator locked; max torque

Coupling phase

Turbine ≈ 90% of impeller; stator freewheels; ~90% efficiency

Lockup phase

Impeller and turbine same speed; 100% efficiency

Stall condition

Turbine stopped while impeller spins

Slippage

Difference in speed between impeller and turbine

Torque multiplication

Increased force from redirected fluid

Torque converter efficiency

~90% in coupling; 100% in lockup

Centrifugal force

Forces fluid outward as speed increases

Fluid dynamics rule

More direction change = more force

Split guide rings

Reduce turbulence and improve efficiency

Torque converter vs fluid coupling

Torque converter has stator and multiplies torque; fluid coupling does not

Torque converter location

Between engine crankshaft and transmission

Non-serviceable torque converter

Welded; cannot be repaired

Serviceable torque converter

Bolted; can be disassembled and repaired

Lockup clutch benefit

Reduces heat, improves fuel economy, eliminates slip

Coupling point

When turbine speed nearly equals impeller speed

Impeller mnemonic

Input (engine side)

Turbine mnemonic

Output (transmission side)

Stator mnemonic

Strength (adds torque)