Foot Brake and Parking Brake
Foot brake and parking brake
Overview
The illustrations above show the rear brake with combined foot brake and parking brake function. The principle for the foot brake function is the same at both front and rear, however.
1. Piston
2. Adjuster screw
3. Adjuster nut
4. Spring holder
5. Return spring
6. Axle
7. Control spring
8. Gasket
9. Throw-out bearing
10. Snap-ring
11. Sealing ring
12. Adjuster piston
13. Arm
14. Eccentric
15. Arm
16. Brake disc
17. Brake caliper
18. Brake pads, outer
19. Brake pads, inner.
General foot brake, front and rear
When braking, the driver presses the brake pedal and an increased hydraulic fluid pressure is generated in the brake system. The increased pressure presses the piston (1) and the inner brake pad (19) against the brake disc (16) at the same time as the brake caliper (17) and the outer brake pad (18) are pressed against the brake disc.
Specific foot brake, rear
Self-adjustment
The rear foot brake contains a self-adjusting parking brake mechanism. The adjustment (compensation for wear on the brake pads and discs) takes place when braking using the foot brake. The clearance in the thread between the adjuster screw (2) and the adjuster nut (3) determines whether adjustment takes place.
When the brake pedal is pressed down, the hydraulic pressure forces out the piston (1). The adjuster nut (3) and the adjuster screw (2) follow this movement.
When the brake pedal is released, the piston is pressed back slightly by the tension in the piston seal. The adjuster nut (3) is pressed against the piston by the control spring (7), at the same time as the return spring (5) presses the adjuster screw (2) against the arm (13).
If the relative movement exceeds the clearance in the thread, the adjuster nut will be twisted to a new position further out on the adjuster screw.
Sealing ring foot brake, front and rear
Braking
The sealing ring (11) is tensioned by means of the adjuster piston being pressed against the brake disc.
Resting position
The tension in the sealing ring (11), which was previously generated by applying the brakes, causes the adjuster piston to be pushed back to the resting position. When the brake pads are worn, the piston is pressed through the sealing ring until the brake pads come into contact with the brake disc. This produces a self-adjustment between brake disc and brake pad.
Parking brake
The parking brake operates on the rear wheels. The parking brake is applied against the brake pads. The brake caliper has an integrated parking brake mechanism. This is self-adjusting between shaft and piston each time after braking, see Specific foot brake, rear. When replacing the brake pads, a special tool is required so that the adjuster nut (3) can be turned back to the original position.
Parking brake lever applied
The tractive force on the brake cable produces a turning movement in the arm (15). The eccentric (14) transfers the force to the arm (13). The arm (13) converts the turning movement to a sliding movement on the adjuster screw (2). The adjuster nut (3) and the sealing cylinder (12) follow the movement towards the brake disc. The piston (1) presses the inner brake pad (19) against the brake disc at the same time as the brake caliper (17) and the outer brake pad (18) are pressed against the brake disc.
When the parking brake lever is released, the components return to the resting position.
20 Adjuster nut
21 Compensator
The upper control lever applies to model years up to and including 2007. The lower control lever applies to model year 2008 -.
Adjustment
Adjusting the mechanical cable for the parking brake is carried out at the lever. The adjuster nut (20) is located by the lever in the passenger compartment. The compensator (21) distributes the braking function between the rear wheel brakes.