What is the most Important system on your vehicle? (The Brake System)

Vocabulary Hydraulics 10.Metering valve Pascal’s laws 11.Brake warning light Brake fluid 12.Brake line with double flare Master cylinder 13.Pads and shoes Wheel cylinder 14.ABS(anti- lock brake system) Caliper 15.Bleeding Disk brake rotor 16.Star wheel adjuster Drum Proportioning valve

Kinetic Energy Your vehicles brake system converts kinetic energy ( energy in motion) to thermal energy (Heat energy) using friction. It takes a lot of friction to stop a 4000 lbs car going 60 MPH ! Friction causes heat – lots of it! Modern cars use hydraulics to create the force needed to make friction and stop the vehicle.

Brake rotor 1200 degrees

Friction Created when one surface rubs on another. The larger the brake pad or shoe the more potential friction. The larger the brake rotor or drum the more potential friction. The friction will change as the force applied changes.

Drum and Disk function

Pascal’s Law Pascal’s law is the law of hydraulics. Pascal’s law states “ a pressure applied to a confined fluid is transmitted undiminished to every portion of the surface of the containing vessel”. The Hydraulic system is used to apply the friction material and stop the car.

Typical 4 wheel basic hydraulic system

hydraulic increase or decrease

Typical Brake system

PART 2 Brake system parts

Master Cylinder Generates the pressure needed in the brake system. The harder you push the pedal the more pressure the master cylinder makes. Keep cyl above Min level

Drum Brake Assembly A cast iron brake drum is attached to the axle of the vehicle and rotates with the wheel. The drum wears over time and can be machined approx .060 larger inside from its original size.

Drum brake – backing plate assembly Wheel cylinder front

Drum brake – Backing plate assembly

Wheel cylinder Receives hydraulic pressure from master cylinder. Applies pressure to the brake shoes. Has two pistons, piston cups, dust boots, and one spring inside the body of the wheel cyl.

Wheel cylinder assembly

Brake shoes Used on a drum brake. Steel backing with some type of composite friction material. Riveted and bonded types. Primary shoe goes towards the front , secondary to back. Never breath brake dust.

Disk Brake Assembly

Brake rotors Typically made of cast iron. Can be vented or non-vented. Will wear or warp over time or with abuse. Can be machined approx .060 before replacement is mandatory. Rotates with axle Non vented vented

Disk brake Calipers The part that receives hydraulic pressure from the master cyl. Can Be fixed or sliding – Can have one or multiple pistons that apply pressure to the brake pads. Calipers parts: Body, piston(s) square cut seal & dust boot(s). Caliper is mounted to spindle or axle housing.

Caliper types: Fixed Four piston caliper (Fixed)

Caliper types : sliding or floating Single piston (Floating)

Brake Pads Caliper presses brake pads against rotor. Brake pads can be made of any combination of metal, composite & synthetic fiber. Must resist extreme heat & pressure while being quiet, predictable and durable. Riveted and bonded types. Friction material should always be thicker than steel backing plate.

Brake Pads checking for wear

When your brake pads are not replaced when warn out they will destroy the rotors.

Brake Fluid Brake fluid is a special glycol based fluid with a high boiling point & good lubricating properties. DOT stands for the department of transportation – only use DOT 3 or 4 fluid unless the manufacture specifies something different. Water absorption causes internal corrosion & lowers boiling point.

Brake lines Steel lines with a double flare on the ends connect the master cylinder to each corner of the car. Flex lines carry brake fluid from the ends of the steel lines to the calipers and wheel cylinders. Flex lines should be inspected regularly

Steel Brake line w/ double flare

Combination Valve The combination valve has three sections. The metering section The warning light switch The proportioning valve The combination valve is typically located below the master cylinder.

Power Brake system The most common type is called a vacuum booster. It uses vacuum from the engine to assist in the application of the brake pedal. Located between the firewall and the master cylinder . Another type of booster is called the hydro- booster. It uses hydraulic pressure generated by a power steering pump to assist in the application of the brakes.

Brake Booster Types Vacuum booster hydro-boost

Power brake booster

Bleeding the brake system The Brake system must be totally free of air. This is because air is compressible and will not transmit pedal motion to the brake pads / shoes. To Bleed air out of a brake system each device in the system has a small bleeder screw at the high point of the part. Foot pressure on the brake pedal pushes brake fluid and air out the bleeder screw. Bleeding can also be done with special equipment like a pressure bleeder or a vacuum bleeder.

Brake Rotor / Drum Machining Brake Rotors and Drums can be machined on a device called a brake lathe. Rotors and Drums should always be checked for minimum thickness or max dia. Under-sized components must be replaced.

ABS ABS stands for: Anti Lock Brake System ABS systems attempt to stop the wheels on the car from locking – this allows the car to be “steered out of an accident” This is accomplished by monitoring wheel speed with sensors. Then a computer is used to control valves that switch brake pressure off and on 15 + times per second. This prevents wheel lock.

ABS System ABS SYSTEM Wheel speed sensor

ABS Parts Pump/Valve unit Wheel speed sensor

Diagnosing ABS problems Standard brake system parts must be in good condition. Scan tool can get DTC’s Always disconnect and bleed pressure from ABS system before bleeding or doing any hydraulic work.

ALL BRAKE WORK !!! Must be checked by instructor before the wheel goes back on !!! No Exceptions !!! Cycle brake pedal after all brake work to verify a firm pedal that will stop car. Be ready to stop the car if there is a brake system problem. ( use E – Brake ) Torque all wheel lugs to factory specifications! Never allow people in car while doing brake work.

Good Luck on your test!