Braking System Operation

Slideshow Contents Part 1: base braking system slides 1-21 Part 2: anti-lock braking systems slides 22-31

Weight Distribution During Braking… braking force is not 50% front & 50% rear front brakes can apply up to 90% of the braking power this depends partly on whether vehicle is front or rear drive (weight distribution) this is why front brakes may have to be replaced 4 or 5 times before the rear brakes need replacement

Weight Distribution During Braking…

Hydraulic Systems

Braking System Components

Master Cylinder converts pedal movement to hydraulic pressure

Master Cylinder Action applied position (pushing on brake pedal)…

Master Cylinder Operation brakes being applied brake pedal released

Caliper Designs fixed caliper pistons on both sides of the brake disc caliper can have 2 or 4 pistons there are some 8 piston versions for race applications little/no flex in the caliper body during heavy braking this results in a firmer brake pedal and increased braking power more expensive to manufacture and repair

Caliper Design floating caliper uses 1 or 2 pistons on one side of the caliper caliper body slides (in reaction to the piston movement) outer brake pad rubs on the outside of the disc

Brake Pad Retraction flexing of the caliper’s square cut o-ring causes piston to retract when the brake pedal is released no return springs required

Drum Brakes

Self Energized, Non-Servo (Leading-Trailing) Drum Brakes bottom of the brake shoes mount to a solid anchor leading (front) brake shoe is self-energized drum rotation increases braking force front (leading) brake shoe is wedged tightly against the drum brake shoes are equal length front (leading) brake shoe maybe thicker than the rear (trailing) used on many front wheel drive vehicles

Self Energized, “Dual-Servo” Drum Brakes one shoe “serves” the other to increase application force note how the bottom of the brake shoes are not mounted on a fixed anchor the brake shoes can pivot or rotate with the drum front (primary) shoe helps increase pressure on rear (secondary) shoe this is referred to as servo action brake shoes are different lengths (longer on back side {secondary shoe}) drum rotation energizes both brake shoes used on many rear wheel drive vehicles when reversing the vehicle, the servo action is reversed - secondary shoe assists the primary shoe – hence the name “dual-servo” primary shoe provides ≈ 30% of the stopping power secondary shoe, which is “served” by the primary shoe provides ≈ 70% of the braking force

Hydraulic Line Connections single piston master cylinder used until 1967 tandem split (fig. 11a) used on rear drive vehicles diagonal split (fig. 11b) used on front drive vehicles Fig. 11a Fig 11b

Brake Hydraulic Control Valves metering valve: delays front brake application until rear brakes have overcome spring tension used on disc/drum system only used mainly on rear wheel drive vehicles

Brake Hydraulic Control Valves proportioning valve: limits hydraulic pressure to rear brakes under hard braking to prevent wheel lock-up has no effect during light to moderate stops

Proportioning Valve Operation heavy braking: pressure on large area of piston forces piston to left this blocks pressure to rear brakes piston will cycle back and forth only allowing a percentage of front brake pressure to the rear light to moderate braking: master cylinder pressure acts on both sides of the piston pressure to front & rear brakes is equal

Brake Hydraulic Control Valves Pressure Differential switch turns on a warning light if hydraulic pressure in one circuit is lost due to a leak

Parking Brakes with Rear Drums mechanical cable actuates the brake shoes (on rear wheels)

Parking Brakes on Rear Discs 2 methods of applying the e-brake on vehicles that use rear disc brakes… 1) cable moves caliper piston out 2) cable pushes out mini brake shoes against the inside of the brake rotor