Brakes and Brake Systems

BrakesBrakes are designed to stop vehicles safely.They use friction as the stopping source of energy.We can have Disc Brakes, usually on the front of the vehicle but can be on the front and rear.We can have Drum Brakes, usually on the rear of vehicles.

Park BrakeSometimes called an emergency brake.Since this brake is used on the rear wheels, it isnt much of an emergency brake.Usually cable operated, using the rear drum brakes.Vehicles with rear disc brakes can use a complete separate drum system on the inside of the rotor for the park brake.NOT A JAKE BRAKE

FrictionThere are two types of friction.Static friction (at rest), Nothing moves.Kinetic friction (in motion), surfaces are sliding on one another.Static friction is very powerful and does not create any heat. It is harder to overcome static friction (To put something in motion is harder than keeping it in motion)

Kinetic friction is less powerful and creates high heat.An example of static friction would be the friction between the tire and the road unless the brakes are locked and skidding on the road. The contact patch of the tire is actually stationary on the road.An example of kinetic friction would be the friction between the brake pads and the rotor on a disc brake system. Disc Brakes

High heat from kinetic frictionThe high heat from kinetic friction has been a problem for manufactures for years.Thick or vented rotors and or brake drums have to be used. (weight)Heat can warp rotors and drums.High heat can cause Brake Fade.

Thought you might like to knowNever pump the brake pedal once you remove a brake caliper or brake drum.What could happen?The caliper piston could blow out of the caliper or the wheel cylinder could blow apart.Disc brakes are self adjusting. There are no adjusters on disc brakes.

Disc BrakesDisc brake systems consist of:A brake rotor this is a heavy metal disc. The brake pads squeeze the rotor to stop the vehicle.Solid hub-less vented hub lessVented Hub-Type

CalipersDisc brake calipers can have one piston (to apply the brake pads) or multiple pistons. Up to 8.They can also be fixed or floatingFloating calipers the caliper must slide on pins or wedges.

Floating calipers usually only have one piston.Solid (mounted) calipers have at least 2 pistons per caliper (one on either side). This allows the separate pistons to apply the brake pads evenly.

Brake padsCome in all shapes and sizes and are made of different materials.

Asbestos is generally not used as a brake pad material anymore because of health hazards associated with asbestos.Heat resistant materials and glues are used with varying amounts of metallic compounds. Generally you get what you pay for.Anti squeal pads may come with the new brake pads. (make sure you use them) squealing brakes will annoy you sooner than later.

Replacing brake padsBrake pads should be replaced before the lining material wears too thin. (about the thickness of a Looney is getting too thin)When brakes wear to a metal to metal point repairs can be expensive.

Make sure all sliding parts (caliper pins and slides) are lubricated (lightly) and free to move.Do not get any grease or lube on the rotor or pad material.You will have to push the piston back into the caliper to make room for the new pads. This can be done with a C clamp but remove the brake master cylinder cover first.Move the piston in slowly and make sure the master cylinder does not overflow.

Check the rotor for scores. (make sure it is thick enough and not rusted too badly)Install the new pads with all clips and pins in the proper places. (take a picture before you start replacement)Once done, replace the master cylinder cover, pump the brake pedal up before you drive and make sure the master cylinder is full.Use the brakes easy at first so the pads wear into the rotors.

Drum Brakes

Self Energizing Drum BrakesHas the anchor at the top. The bottom is free to move forward or back. The drum grabs the primary shoe and it applies the secondary shoe. The secondary shoe does most of the braking therefore the lining is longer and harder.

Non Self Energizing

Drum Brake Spring Kit

Drum Brake Shoe ReplacementHave a manual or take a picture before you begin.Springs must go back on exactly where they came off.If shoes have a long and a short lining, the long lining always goes toward the rear of the car.Drum brakes must always be adjusted before the park brake cables. Never adjust the rear brakes using the park brake adjuster.

Make sure wheel cylinders are not seized.

Be very careful that everything goes back exactly where it came from. It is very hard to see with the hub or axle in the way.

You should always plan to replace all springs when you replace the brake shoes. The springs could be rusted or stretch or brake when you remove them and they are not very expensive to replace.

Antilock BrakesUse the exact same braking system as a non-antilock brake system, only the pressure to apply and or release the brakes can be controlled by a module or computer if a wheel locks during braking.There are RWAL (rear wheel antilock) systems, 3-chanel antilock systems and 4-chanel antilock systems.

Additional ComponentsAntilock brake systems make use of a computer or controller.They use an enhanced master cylinder containing a hydraulic pump of some sort and a valve mechanism connected to the brakes. They have wheel speed sensors for each wheel.

RWAL BrakesRear wheel antilock brakes are generally on light trucks, vans and SUVs.Only the rear wheels have antilock capabilities. The front wheels are a normal brake system.This helps control the rear wheel lock-up on vehicles with varying loads and prevents the rear from sliding sideways while braking.

Three Channel Antilock BrakesThree channel simply means there are three separate braking systems on the vehicle.Either front wheel can be applied or released separately and the rear has one channel for both rear wheels.The computer can release either front wheel if one is skidding or the rear wheels if they are skidding.This system allows us the ability to steer the vehicle in an emergency stop.

Four Channel Antilock BrakesThis simply means each wheel has its own channel and can be applied and released separately.This gives you the best vehicle control during an emergency stop.

How They WorkThey dont unless a wheel locks up.The speed of each wheel is monitored during braking by a signal from a wheel speed sensor sent to a computer.When all wheels are slowing evenly, nothing happens. (normal braking)If one wheel is turning slower than the rest the computer will, stop applying pressure to that wheel, then, if necessary, release pressure to the skidding wheel and then reapply pressure again.

This can all happen about 5 to 10 times per second, depending on the system.This system will only work if you let it. (use it properly)Hold pressure on the brake pedal and do not pump the brakes.

Why, Antilock Brakes?At first we were told they could stop a vehicle faster, under all driving conditions.This was found to be untrue. True under most conditions but not all.Now we are being told, antilock brake systems give us vehicle control and stability during panic braking.Very true if you can be trained to steer around an accident and not hang on tight and prepare for the crash like I do.

Master CylindersMaster cylinders have been Tandem (by law) since 1980.Tandem means, one master cylinder operates two completely separate hydraulic systems for the brakes.

These systems can be conventionally split Which means one hydraulic system operates the front wheel brakes and the other operates the rear wheel brakes.

The other is diagonally split one hydraulic system operates the right front and the left rear brakes and the other operates the left front and the right rear brakes.

Bleeding the BrakesRemoving all air from the hydraulic system or changing the fluid in the system.When parts are replaced only bleed the wheels necessary.When the whole system has to be bleed start at the wheel farthest from the master cylinder. The right rear.

Dont Pump The Pedal!!!!Pumping the brake pedal can aerate (tiny air bubbles) the brake fluid.Air in brake systems cause a soft, spongy brake pedal or no brakes at all.The best way to bleed brakes is to have two people. (one to operate the brake pedal and the other to work the bleeder screw.The person in the vehicle pushes the brake pedal down and holds it there.

The other person opens the bleeder screw and lets the air/fluid out. Then snug it back up.The person in the vehicle then lets the pedal up and gives it a few seconds before pushing it back down again.This continues until nothing except pure brake fluid comes out of the bleeder screw.Move onto the next wheel. (conventional split = left rear, diagonal split = left front) You always bleed one hydraulic system before starting the other.Make sure the master cylinder does not run out of fluid!!!!

One Person Method

Make Sure The Bleeder Screw Is At The Highest Point.

Other ValvesCombination ValveCombination valves can consist of a number of other valves.Pressure differential switch.Main metering valve.Proportioning valve.

Pressure Differential SwitchThis switch is designed to sense pressure differences in the two hydraulic systems and warn the driver when there is a difference in pressure.This is usually caused by a leak in one of the hydraulic systems.

Main Metering ValveInstalled on vehicles with front disc and rear drum brakes.Because it takes a little pressure to overcome the spring tension of the drum brakes this valve delays pressure to the front brakes until the rear start to apply.Applying the rear brakes first helps keep the vehicle straight while stopping.

Proportioning ValveThe proportioning valve reduces the total pressure to the rear brakes trying to reduce the chance of rear wheel lockup.A height sensing valve can also be used for this purpose.When a vehicle is loaded heavily, the height sensing valve will allow more pressure to the rear brakes and less pressure when the ride height is high (vehicle unloaded)

Brake LinesAll brake lines must be made from steel tubing.You can buy them in lengths or make them yourself.All brake lines must be high pressure double flared.

Flares and Tools