Brakes slow cars and trucks down by converting kinetic energy into heat. The way it works is that the movement of your foot pushing on your brake pedal actuates the hydraulic brake master cylinder, pushing brake fluid to the brake cylinders or calipers at every wheel to apply friction to slow the turning wheels.
Image Source: Flickr
The brake master cylinder, which a brake pedal pushes into, can be constructed from either aluminum or cast iron. It bolts to a vacuum booster assembly because of a flange. The brake pedal pivots near the firewall and uses leverage to apply a strong mechanical force to the brake master cylinder piston.
Many old vehicles had drums on the rear and sometimes on the front. According to this Nissan dealer’s Service Manager, who spoke to use from Laurel, MS, a drum brake system consists of four main parts on the axle: the backing plate, hydraulic wheel cylinder, brake shoes, and the brake drum. If you spend time in mud and water, a rear disc brake conversion may be high on your priority list. For many cars, you can convert from rear drum brakes to rear discs using available kits.
With a drum brake, the wheel cylinder mounted to the brake backing plate changes the hydraulic line pressure from the master cylinder into a mechanical movement and force onto the brake shoes, with all drum assemblies. Often, only one wheel cylinder is used for a wheel, but occasionally designs will use two-wheel cylinders, one for each brake shoe per wheel.
In the last ten years or so discs have become common on rear axles. Disc brakes are typically light in weight, easy to service, and brake quite consistently. Disc brake calipers are also inherently self-adjusting by design.
There are three kinds of disc brake calipers: fixed calipers, floating calipers, and sliding calipers. A fixed caliper has at least one piston, on each side of the rotor. The caliper is bolted to the steering knuckle or other caliper mount. Pistons move equally from each side of the rotor to apply pressure directly on each of the rotor’s sides.
In contrast, a floating caliper has only one large piston (or two smaller ones) located on the caliper’s inboard side. Since force must be applied equally to both of the rotor’s sides, the floating caliper must be able to actuate both pads. The caliper is bolted to the mount with pins, and the caliper slides back and forth on bushings or sleeves. The inboard pad sits directly on the piston. The outboard pad sits in the caliper frame. When the brakes are applied, the piston moves outward, which pushes the inboard pad into the rotor. At the same time, the force exerted backward from the piston onto the caliper frame causes the frame to move inboard, bringing the outboard pad into contact with the rotor. Both pads press on the rotor because of this.
A sliding caliper operates quite similarly to a floating caliper. However, instead of using a set of pins, a sliding caliper rides in a set of machined guides.