1 parking brake systems brake pedal assembly transmission interlock
TRANSCRIPT
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Parking Brake Systems
Brake Pedal Assembly
Transmission Interlock
Parking Brake Systems
Brake Pedal Assembly
Transmission Interlock
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RequirementsRequirements
• Federal regulations require all road vehicles to have a mechanical or electrical parking brake [emergency brake/hand brake] system.
• The Parking Brake serves two functions:– Prevents vehicle movement when parked.– Provides an alternative method of slowing and
bringing the vehicle to a stop in the event of a hydraulic failure.
• Federal regulations require all road vehicles to have a mechanical or electrical parking brake [emergency brake/hand brake] system.
• The Parking Brake serves two functions:– Prevents vehicle movement when parked.– Provides an alternative method of slowing and
bringing the vehicle to a stop in the event of a hydraulic failure.
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Parking Brake IndicatorParking Brake Indicator
• Federal regulations also require that the parking brake indicator have a warning light system to let the driver know if the parking brake is applied.
• Most manufactures add an audible chime warning to further warn the driver that the parking brake is applied.
• Federal regulations also require that the parking brake indicator have a warning light system to let the driver know if the parking brake is applied.
• Most manufactures add an audible chime warning to further warn the driver that the parking brake is applied.
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Parking Brake IndicatorParking Brake Indicator• The parking brake
warning light is shared with the hydraulic system failure warning system. This provides a simple way of proving that the indicator light is working properly.
• The parking brake warning light is shared with the hydraulic system failure warning system. This provides a simple way of proving that the indicator light is working properly.
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System componentsSystem components
• A lever mechanism inside the brake unit to apply the pads or shoes
• Flexible cables to connect the brake unit mechanically to the pedal or lever inside the car.
• An equalizer bar to equally divides the force to both brakes
• A lever or pedal assembly to apply the brake and provide mechanical advantage.
• A ratchet mechanism to hold the brakes applied.
• A release mechanism to disengage the ratchet.
• A lever mechanism inside the brake unit to apply the pads or shoes
• Flexible cables to connect the brake unit mechanically to the pedal or lever inside the car.
• An equalizer bar to equally divides the force to both brakes
• A lever or pedal assembly to apply the brake and provide mechanical advantage.
• A ratchet mechanism to hold the brakes applied.
• A release mechanism to disengage the ratchet.
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Cables, pedals and levers Cables, pedals and levers
• On most cars the parking brake is cable operated but on some late model European cars the parking brake is electrically actuated by stepper motors in the calipers.
• The parking brake can be actuated by a pedal to the left of the brake and clutch pedal, by a ‘T’-handle under the dash to the right of the steering column or by a lever which may be mounted on the console or on the door sill to the left of the driver.
• The pedal or lever mechanism has a ratchet mechanism to hold the parking brake applied and a release button.
• On most cars the parking brake is cable operated but on some late model European cars the parking brake is electrically actuated by stepper motors in the calipers.
• The parking brake can be actuated by a pedal to the left of the brake and clutch pedal, by a ‘T’-handle under the dash to the right of the steering column or by a lever which may be mounted on the console or on the door sill to the left of the driver.
• The pedal or lever mechanism has a ratchet mechanism to hold the parking brake applied and a release button.
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Automatic parking brake releaseAutomatic parking brake release
Some vehicles that use a pedal type mechanism have a vacuum release diaphragm that automatically releases the parking brake when the transmission is taken out of park and the engine is running.
Some vehicles that use a pedal type mechanism have a vacuum release diaphragm that automatically releases the parking brake when the transmission is taken out of park and the engine is running.
ManifoldVacuum
NeutralSafetySwitch
Vent
Vacuum DiaphragmManual
ReleaseLever
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CablesCables
• Most vehicles have a front cable that connects the parking brake lever to an equalizer bar.
• The equalizer bar is then connected to a left and right rear cable.
• Short wheelbase vehicles may have the left and right side cables connected directly to the center console mounted lever assembly.
• The equalizer bar allows the tension applied to the cables to be divided equally to both brake cables.
• Most vehicles have a front cable that connects the parking brake lever to an equalizer bar.
• The equalizer bar is then connected to a left and right rear cable.
• Short wheelbase vehicles may have the left and right side cables connected directly to the center console mounted lever assembly.
• The equalizer bar allows the tension applied to the cables to be divided equally to both brake cables.
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Flexible brake cablesFlexible brake cables
• The cables connecting the brake assembly to the equalizer bar and front cable assembly are two piece coaxial assemblies.
• A multi-strand stainless steel cable slides back and forth inside a spiral wound and rubber sheathed outer conduit.
• The cable ends are crimped the stainless steel inner cable
• Rubber boots are both ends keep dirt and moisture out of the outer conduit.
• A spiral spring is usually incorporated into the outboard end to serve as a release mechanism
• The cables connecting the brake assembly to the equalizer bar and front cable assembly are two piece coaxial assemblies.
• A multi-strand stainless steel cable slides back and forth inside a spiral wound and rubber sheathed outer conduit.
• The cable ends are crimped the stainless steel inner cable
• Rubber boots are both ends keep dirt and moisture out of the outer conduit.
• A spiral spring is usually incorporated into the outboard end to serve as a release mechanism
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Parking brake locationParking brake location
• Most manufactures incorporate the parking brake into each of the rear brake assemblies.
• Older SAAB’s and Subaru’s incorporated the parking brake into the front brakes.
• Some medium duty trucks mount a cable operated drum brake at the back of the transmission that mechanically holds the driveshaft from turning when the parking brake is applied.
• Most manufactures incorporate the parking brake into each of the rear brake assemblies.
• Older SAAB’s and Subaru’s incorporated the parking brake into the front brakes.
• Some medium duty trucks mount a cable operated drum brake at the back of the transmission that mechanically holds the driveshaft from turning when the parking brake is applied.
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Parking Brake for Drum BrakesParking Brake for Drum Brakes
• The rear drum brakes have a lever attached to one of the shoes via a pivot pin.
• A parking brake strut connects the lever to the opposite shoe.
• When the lever is pulled inward by the cable the strut applies equal pressure to both shoes.
• On non-servo brakes the automatic adjuster star wheel is incorporated into the parking brake strut.
• The rear drum brakes have a lever attached to one of the shoes via a pivot pin.
• A parking brake strut connects the lever to the opposite shoe.
• When the lever is pulled inward by the cable the strut applies equal pressure to both shoes.
• On non-servo brakes the automatic adjuster star wheel is incorporated into the parking brake strut.
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Parking brake operationParking brake operation
• The parking brake lever acts like a pry bar – forcing the shoes apart
• The parking brake lever acts like a pry bar – forcing the shoes apart
AnchorPin
• When the parking brake is applied the shoes are forced away from the anchor pin.
• When the parking brake is applied the shoes are forced away from the anchor pin.
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Parking Brake for Disc BrakesParking Brake for Disc Brakes
• There are two types of parking brake designs used on vehicles with 4 wheel disc brakes.
– Actuating calipers – Drum in Hat
• There are two types of parking brake designs used on vehicles with 4 wheel disc brakes.
– Actuating calipers – Drum in Hat
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Actuating CaliperActuating Caliper
• The actuating caliper can be identified by the lever on inboard side of the cylinder.
• The actuating caliper can be identified by the lever on inboard side of the cylinder.
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Actuating calipers Actuating calipers
• A screw and lever mechanism is added to the caliper.
• A screw and lever mechanism is added to the caliper.
• The lever turns a screw – which applies mechanical pressure directly to the brake pad.
• An internally threaded adjusting cone is located between the screw and back of the piston.
• The lever turns a screw – which applies mechanical pressure directly to the brake pad.
• An internally threaded adjusting cone is located between the screw and back of the piston.
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Actuating CaliperActuating Caliper
• As the pads wear down the pistons move outward - the adjusting cone rotates as it unwinds along the screw thread.
• As the pads wear down the pistons move outward - the adjusting cone rotates as it unwinds along the screw thread.
PrimarySeal
Shaft Seal
SecondarySeal
Lever
Adjusting Cone
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Pad replacement – Actuating caliperPad replacement – Actuating caliper
• Special tools are needed to rotate the piston as pressure is applied.
• Special tools are needed to rotate the piston as pressure is applied.
• Replacing pads requires that the piston be rotated as it is pushed back into the caliper bore.
• Replacing pads requires that the piston be rotated as it is pushed back into the caliper bore.
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Drum in Hat Drum in Hat
• A dedicated set of brake shoes is mounted on a small backing plate on the axle.
• Since these shoes are only use when the car is stationary they should never wear out.
• A lever and strut is used to actuate the brake.• A star wheel mounted opposite the lever/strut provides for
periodic manual adjustment.
• A dedicated set of brake shoes is mounted on a small backing plate on the axle.
• Since these shoes are only use when the car is stationary they should never wear out.
• A lever and strut is used to actuate the brake.• A star wheel mounted opposite the lever/strut provides for
periodic manual adjustment.
• A small brake drum – about 7” dia. – is machined into the inside of the rotor ‘hat’ as a friction surface for the shoes.
• A small brake drum – about 7” dia. – is machined into the inside of the rotor ‘hat’ as a friction surface for the shoes.
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‘Drum in Hat’ type parking brake ‘Drum in Hat’ type parking brake Since the brake unit is so small removal of the axle flange or bearing assembly is necessary to gain access to the components.
Since the brake unit is so small removal of the axle flange or bearing assembly is necessary to gain access to the components.
CaliperMounting ear
Lever mountedbehind leading shoe
Star WheelAdjuster
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‘Drum in Hat’ type parking brake ‘Drum in Hat’ type parking brake
• Brake assembly as seen from the back
• Brake assembly as seen from the back
Caliper
Cable
ParkingBrake Lever
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Parking Brake Test procedureParking Brake Test procedure
• Fine a place where it is safe to test the parking brake.
• Apply the parking brake then place the transmission in gear.
• Open the throttle partially and see if the vehicle moves.
• The parking brake is not designed to hold the vehicle at wide open throttle – but it should hold the vehicle at light to moderate throttle openings.
• Make sure the brake warning indicator illuminates when the parking brake is applied.
• Fine a place where it is safe to test the parking brake.
• Apply the parking brake then place the transmission in gear.
• Open the throttle partially and see if the vehicle moves.
• The parking brake is not designed to hold the vehicle at wide open throttle – but it should hold the vehicle at light to moderate throttle openings.
• Make sure the brake warning indicator illuminates when the parking brake is applied.
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Parking brake balance testParking brake balance test
• For this test you need a wide area of dry road with no traffic
• Pull the release lever or push in the release button during the test so that you can immediately release the parking brake if the vehicle begins to swerve.
• At a road speed of about 30 mph apply the parking brake lightly and check to see if the vehicle pulls to either side
• If the vehicle pulls to either side there may be a problem in the system and further inspection will be necessary
• For this test you need a wide area of dry road with no traffic
• Pull the release lever or push in the release button during the test so that you can immediately release the parking brake if the vehicle begins to swerve.
• At a road speed of about 30 mph apply the parking brake lightly and check to see if the vehicle pulls to either side
• If the vehicle pulls to either side there may be a problem in the system and further inspection will be necessary
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Number of clicks testNumber of clicks test
• Most manufactures specify the number of clicks or the distance the parking brake lever must travel before the parking brake becomes effective.
• Typically 3 to 5 clicks are heard before a drag is noticed at the wheels. This insures that there is a running clearance between the shoes and drums.
• Most manufactures specify the number of clicks or the distance the parking brake lever must travel before the parking brake becomes effective.
• Typically 3 to 5 clicks are heard before a drag is noticed at the wheels. This insures that there is a running clearance between the shoes and drums.
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Number of clicks testNumber of clicks test
• At 10 to 12 clicks the vehicle should not move under light throttle and you should not be able to turn the wheels by hand . The parking brake should feel tight at this point although you may be able to apply a few more clicks.
• At 10 to 12 clicks the vehicle should not move under light throttle and you should not be able to turn the wheels by hand . The parking brake should feel tight at this point although you may be able to apply a few more clicks.
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Visual inspection – Drum brakesVisual inspection – Drum brakes
• With the parking brake released and the drum removed check that the shoes are in full contact with the anchor pin.
• A gap between the anchor pin and the shoe indicates a frozen cable or an over adjust brake cable
• Apply the parking brake and check to see that the shoes are now spread slightly apart and there is a gap now between one of the shoes and the anchor pin
• Release the parking brake and check to see that the shoes are now back in contact with the anchor pin
• Grasp the parking brake strut with a pair of pliers and see if the strut can move back and forth slightly.
• If the strut is tight there may be a problem with cables or adjustment
• With the parking brake released and the drum removed check that the shoes are in full contact with the anchor pin.
• A gap between the anchor pin and the shoe indicates a frozen cable or an over adjust brake cable
• Apply the parking brake and check to see that the shoes are now spread slightly apart and there is a gap now between one of the shoes and the anchor pin
• Release the parking brake and check to see that the shoes are now back in contact with the anchor pin
• Grasp the parking brake strut with a pair of pliers and see if the strut can move back and forth slightly.
• If the strut is tight there may be a problem with cables or adjustment
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Visual InspectionVisual Inspection
• With the parking brake released the brake shoes should be in contact with the anchor pin.
• With the parking brake released the brake shoes should be in contact with the anchor pin.
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Visual InspectionVisual Inspection
• You should be able to move the brake strut slightly to the left against slight spring tension.
• You should be able to move the brake strut slightly to the left against slight spring tension.
Strut
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Drum In Hat adjustmentDrum In Hat adjustment
• The ‘Drum in Hat’ type brake needs to be adjusted periodically.
• Newer vehicles normally have a slot in the backing plate for star wheel adjustment.
• Older vehicles may have a hole in the axel flange and rotor to facilitate adjustment.– When installing rotors make sure that the
adjustment hole in the rotor aligns with the hole in the axle flange.
• The ‘Drum in Hat’ type brake needs to be adjusted periodically.
• Newer vehicles normally have a slot in the backing plate for star wheel adjustment.
• Older vehicles may have a hole in the axel flange and rotor to facilitate adjustment.– When installing rotors make sure that the
adjustment hole in the rotor aligns with the hole in the axle flange.
• Adjust the star wheel with a brake spoon until a slight drag is felt when the rotor is turned by hand, then back off a few clicks.
• The star wheel can be turned in either direction – so you don’t have to push a pawn away from the star wheel to loosen the adjustment
• Adjust the star wheel with a brake spoon until a slight drag is felt when the rotor is turned by hand, then back off a few clicks.
• The star wheel can be turned in either direction – so you don’t have to push a pawn away from the star wheel to loosen the adjustment
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‘Drum in Hat’ type parking brake ‘Drum in Hat’ type parking brake
• Slot for adjusting star wheel
• Slot for adjusting star wheel
Caliper
ParkingBrake Lever
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Brake cable adjustmentBrake cable adjustment
• Parking brake cables rarely need adjustment. • The only time they are regularly adjusted is
after cable replacement.• The cables are adjusted last – after the star
wheel adjustments are made.• Each manufacture publishes a procedure –
typically they are tightened until a set number of clicks is heard as the parking brake is applied.
• On vehicles with pedal type parking brakes the adjuster is normally located underneath the car.
• Parking brake cables rarely need adjustment. • The only time they are regularly adjusted is
after cable replacement.• The cables are adjusted last – after the star
wheel adjustments are made.• Each manufacture publishes a procedure –
typically they are tightened until a set number of clicks is heard as the parking brake is applied.
• On vehicles with pedal type parking brakes the adjuster is normally located underneath the car.
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Brake cable adjustmentBrake cable adjustment
• On vehicles with the parking brake lever on the center console the console cover may need to be removed to gain access to the adjustment nuts.
• On vehicles with the parking brake lever on the center console the console cover may need to be removed to gain access to the adjustment nuts.
Equalizer Bar
Adjustment Nut
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Brake cable replacementBrake cable replacement
• Binding parking brake cables should be replaced.• Occasionally you can loosen up a binding cable but
the repair is temporary.• Brake cables are retained to the backing plate at
their outboard ends by a barbed end. As the cable is pushed through the hole in the backing plate it springs open and locks.
• Removal is accomplished by using a small stainless steel hose clamp to squeeze the barbs back into the center so that the cable can be pulled out of the backing plate.
• Actuating calipers typically retain the cable using a spring steel c-clip.
• Binding parking brake cables should be replaced.• Occasionally you can loosen up a binding cable but
the repair is temporary.• Brake cables are retained to the backing plate at
their outboard ends by a barbed end. As the cable is pushed through the hole in the backing plate it springs open and locks.
• Removal is accomplished by using a small stainless steel hose clamp to squeeze the barbs back into the center so that the cable can be pulled out of the backing plate.
• Actuating calipers typically retain the cable using a spring steel c-clip.
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Service brake pedal assemblyService brake pedal assembly
• The brake pedal assembly consists of:– Pedal shaft support brackets welded to the
body.– Pedal shaft – supports both brake and clutch
pedals.– Brake pedal.– Brake light switch assembly.– Brake / Transmission interlock cable assembly
[on vehicles using mechanical interlock].
• The brake pedal assembly consists of:– Pedal shaft support brackets welded to the
body.– Pedal shaft – supports both brake and clutch
pedals.– Brake pedal.– Brake light switch assembly.– Brake / Transmission interlock cable assembly
[on vehicles using mechanical interlock].
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Pedal assemblyPedal assembly
• The pedal rotates on a shaft mounted above the pedals
• The brake pedal is connected to the power booster via an actuating rod that attaches to the pedal by means of a Clevis pin.
• The clevis pin is in turn retained by a small cotter pin.
• The brake switch normally connected to the pedal by a spring loaded plunger– Older vehicles use a switch similar to a
refrigerator door switch – when the pedal is in contact the switch is off – when it moves away the switch is on
– Modern vehicles use a multi-function brake switch
• The pedal rotates on a shaft mounted above the pedals
• The brake pedal is connected to the power booster via an actuating rod that attaches to the pedal by means of a Clevis pin.
• The clevis pin is in turn retained by a small cotter pin.
• The brake switch normally connected to the pedal by a spring loaded plunger– Older vehicles use a switch similar to a
refrigerator door switch – when the pedal is in contact the switch is off – when it moves away the switch is on
– Modern vehicles use a multi-function brake switch
PedalShaft
Actuator rodfor powerbooster
BrakeSwitch
ClevisPin
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Five functions of the brake switchFive functions of the brake switch
• Operates the brake lights.• Disengages the cruise control when the
brake pedal is depressed.• Disengages ABS system when brake pedal
is not depressed. • Completes the circuit for the starter relay
when the pedal is depressed.• Completes the circuit for the transmission
selector interlock solenoid [on vehicles using electrical interlock].
• Operates the brake lights.• Disengages the cruise control when the
brake pedal is depressed.• Disengages ABS system when brake pedal
is not depressed. • Completes the circuit for the starter relay
when the pedal is depressed.• Completes the circuit for the transmission
selector interlock solenoid [on vehicles using electrical interlock].
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Brake / Transmission InterlockBrake / Transmission Interlock
• Modern cars and trucks with automatic transmissions are required to have mechanism that prevents the transmission selector from moving out of the park position when the driver’s foot is not on the brake pedal.
• The interlock can be either electrical or mechanical.
• Modern cars and trucks with automatic transmissions are required to have mechanism that prevents the transmission selector from moving out of the park position when the driver’s foot is not on the brake pedal.
• The interlock can be either electrical or mechanical.
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Mechanical Brake / Transmission InterlockMechanical Brake / Transmission Interlock
• A flexible cable similar to a parking brake cable – but much smaller is connected to a slot in the upper end of the brake pedal
• The other end of the cable operates a small lever on the base of the transmission selector quadrant.
• There is a notch in the quadrant that the lever can slide in and out of. When the lever is in the notch the selector is locked in park.
• When the cable pulls the lever out of the notch the selector can be moved into any gear range.
• A flexible cable similar to a parking brake cable – but much smaller is connected to a slot in the upper end of the brake pedal
• The other end of the cable operates a small lever on the base of the transmission selector quadrant.
• There is a notch in the quadrant that the lever can slide in and out of. When the lever is in the notch the selector is locked in park.
• When the cable pulls the lever out of the notch the selector can be moved into any gear range.
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Mechanical Brake / Transmission InterlockMechanical Brake / Transmission Interlock
Interlock Cable
Interlock Pawl
Shifter Cable
PR N D 2
1
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Electrical Brake / Transmission InterlockElectrical Brake / Transmission Interlock
• A solenoid mounted on the gear selector assembly over the notch in the quadrant.
• When the solenoid is energized the solenoid pin is pulled out of the notch. When it is de-energized a spring in the solenoid pushes it into the notch.
• The solenoid is controlled by the brake switch.
• A solenoid mounted on the gear selector assembly over the notch in the quadrant.
• When the solenoid is energized the solenoid pin is pulled out of the notch. When it is de-energized a spring in the solenoid pushes it into the notch.
• The solenoid is controlled by the brake switch.
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Override buttonOverride button
• An override button is required on the electrical type interlock in the event that the vehicle needs to be moved when it’s battery is dead.
• In some cases this takes the form of a slot on the console next to the shifter that is the same size as the ignition key – although any key can activate it.
• An override button is required on the electrical type interlock in the event that the vehicle needs to be moved when it’s battery is dead.
• In some cases this takes the form of a slot on the console next to the shifter that is the same size as the ignition key – although any key can activate it.
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