Astra G
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Brake Calipers for Rear Wheel Brakes The brake caliper is a floating combination caliper; the service and parking brakes both act on the brake linings. The brake caliper housing of the combination caliper is made of aluminium.
• Service Conventional piston resetting equipment must not be used, as there is a risk that this would cause defects to the brake piston. In the interest of safety, Piston Resetting Tool KM-6007 must be used to turn back the brake caliper piston.
9.2.2.2 Brake Calipers for Rear Wheel Brakes (continued) The floating caliper has all the advantages of a disk brake and combines the hydraulic service brake and the mechanical parking brake into one unit - see illustration G 4684. Adjustment of the service and parking brakes is automatic. Hydraulic function (service brake) The service brake is hydraulically actuated and functions according to the principle of a conventional floating caliper brake. However, a fraction of the hydraulic pressure is required to overcome the defined resistance of the spring integrated into the brake caliper (4). Parking brake function When the parking brake is actuated, the actuation lever (6) on the brake caliper (3) turns the rotating disk (7). 3 balls (8) in floating bearings convert the radial motion into an axial movement. The thrust disk (5) only moves in the axial direction, and transfers the force to the adjuster sleeve (10). The stop bolt (9) prevents the thrust disk from rotating. Once the function clearance between the adjuster sleeve and the adjuster bolt (11) has been overcome, the motion takes effect on the piston (2), brake linings (1) and finally the brake disk. When the parking brake is released, the actuation elements are returned to the starting position by the spring (4). The piston is returned to its position by the seal ring in the conventional manner.
9.2.2.2 Brake Calipers for Rear Wheel Brakes (continued)
9.2.2.2 Brake Calipers for Rear Wheel Brakes (continued) Automatic Parking Brake Adjustment - Compensation of Brake Lining Wear When pressure is applied (service brake), the piston (1) is moved to the left against the brake lining. If, during this procedure, the function clearance between the adjuster sleeve (3) and the adjuster bolt (2) is overcome before the brake lining contacts the brake disk, the adjuster bolt is lifted on its conical seat in the piston. Each additional forwards motion of the piston causes a mechanical force to be exerted on the adjuster bolt via the retaining ring (4), disks (6), spring disks (7) and ball bearings (8). At the same time, the hydraulic pressure acting in the same direction supports this effect. The force applied turns the adjuster screw in the thread of the adjuster sleeve and it moves, like the piston, to the left. This procedure is repeated until a pressure compensation or pressure increase in the piston takes effect on the adjuster screw. Pressure limitation If a preset hydraulic pressure exceeds the pretension force of the spring (5), the adjuster sleeve can no longer be held in contact with the axially moving disk. The adjuster sleeve moves the adjuster bolt to the left until the bolt makes contact in the conical seat of the piston. It is then held in position by friction, preventing further or excessive adjustment.
9.2.2.2 Brake Calipers for Rear Wheel Brakes (continued)
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