1. Parking Brake Systems Brake Pedal Assembly Transmission Interlock

2. Requirements
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.

3. Parking 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.

4. Parking 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.

5. System 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.

6. 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.

7. Automatic 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.
Vacuum
Diaphragm
Manual
Release
Lever
Manifold
Vacuum
Vent
Neutral
Safety
Switch

8. 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.

9. Flexible 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

10. Parking 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.

11. Parking 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.

12. Parking brake operation
Anchor
Pin
The parking brake lever acts like a pry bar – forcing the shoes apart
When the parking brake is applied the shoes are forced away from the anchor pin.

13. Parking 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

14. Actuating Caliper
The actuating caliper can be identified by the lever on inboard side of the cylinder.

15. Actuating calipers
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.

16. Actuating Caliper
Primary
Seal
Adjusting Cone
Shaft Seal
Lever
Secondary
Seal
As the pads wear down the pistons move outward - the adjusting cone rotates as it unwinds along the screw thread.

17. Pad replacement – Actuating caliper
Replacing pads requires that the piston be rotated as it is pushed back into the caliper bore.
Special tools are needed to rotate the piston as pressure is applied.

18. Drum in Hat
A small brake drum – about 7” dia. – is machined into the inside of the rotor ‘hat’ as a friction surface for the shoes.
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.

19. ‘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.
Lever mounted
behind leading shoe
Caliper
Mounting ear
Star Wheel
Adjuster

20. ‘Drum in Hat’ type parking brake
Caliper
Parking
Brake Lever
Brake assembly as seen from the back
Cable

21. Parking 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.

22. Parking 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

23. Number 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.

24. Number 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.

25. Visual 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

26. Visual Inspection
With the parking brake released the brake shoes should be in contact with the anchor pin.

27. Visual Inspection
You should be able to move the brake strut slightly to the left against slight spring tension.
Strut

28. Drum 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.
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

29. ‘Drum in Hat’ type parking brake
Brake Lever
Caliper
Slot for adjusting star wheel

30. Brake 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.

31. Brake cable adjustment
Equalizer Bar
Adjustment Nut
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.

32. Brake 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.

33. Service 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].

34. Pedal 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
Brake
Switch
Pedal
Shaft
Clevis
Pin
Actuator rod
for power
booster

35. Five 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].

36. Brake / 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.

37. Mechanical 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.

38. Mechanical Brake / Transmission Interlock
Interlock Cable N R D 2 P 1
Shifter Cable
Interlock Pawl

39. Electrical 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.

40. Override 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.