Front Disc Brakes
DESCRIPTIONThe front disc brake system consists of the following components:
- Disc brake caliper (4 piston opposed fixed)
- Brake shoes and linings
- Brake rotor
These components are described in detail below.
The disc brake caliper applies the brake pads to the brake rotor. This is done using a 4 piston opposed fixed caliper on each side of the vehicle. Each caliper body is cast aluminum, and is 2 individual pieces which are held together by 4 attaching bolts. Each caliper half houses 2 pistons, 38 mm and 42 mm in size. The pistons are mounted in the caliper halves so that the 38 mm piston is on the bottom and the 42 mm is on top when the caliper is mounted on the vehicle. The 2 halves of the caliper are hydraulically connected by means of an external brake tube on the bottom of the caliper assembly. Each caliper half has an individual bleeder screw at the top of the caliper half and each side must be individually bled. The caliper bolts directly to the steering knuckle of the vehicle by means of 2 machined mounting bosses on the inboard caliper half.
Two brake shoes are used on each side of the vehicle, one on each side of the brake rotor. The brake shoe lining material is a semi-metallic non-asbestos formula. The brake lining material used has been specifically formulated to meet the braking requirements of this vehicle. When brake shoes are replaced, only brake shoes meeting the Original Equipment Manufacturer formulation (such as Mopar(R) replacement parts) should be used to maintain the original braking performance of this vehicle. See Specifications for the brake lining requirements.
One brake rotor is used on each side of the vehicle. It mounts on the hub and bearing. The rotor is made of iron and is vented to help cool it during brake applications.
OPERATION
The disc brake caliper operates in the following manner. As the driver steps on the brake pedal, hydraulic pressure from the master cylinder is applied to the rear of the pistons (4.) inside each caliper. This action pushes the pistons outward, applying the shoes against the brake rotor.
Fig. 2 Piston Seal Function:
One square cut rubber piston seal is located in the machined seal groove of each piston bore. There are 4 piston bores, 2 located in each half of the caliper assembly. The seals provide a hydraulic seal between the caliper pistons and the caliper piston bore.
The piston seals also provide a secondary function. The aid in pulling the piston back into the piston bore of the caliper assembly when the brake pedal is released. This maintains the proper brake shoe to rotor clearance. The ability of the piston seals to pull the pistons back into the caliper bores is illustrated in the figure. As the piston moves out of the caliper bore when the brake pedal is applied, the piston seal becomes distorted. When the brake pedal is released and hydraulic pressure removed from the piston, the piston seal returns to its original shape, pulling the piston back into the caliper bore.
A molded rubber dust boot is installed in a groove of each caliper bore and piston. The purpose of this dust boot is to keep contamination from the wall of the caliper bore and piston.
The dust boots mount in the caliper bore openings and in a groove of each piston.
The purpose of brake shoes is to slow down and stop the brake rotor. The purpose of the brake rotor is to slow down and stop the front wheels of the vehicle from turning when the brakes are applied.