Basic Brakes
Split systems/dual master cylinders
Used exclusively since 1960’s Most use front/rear split Some use diagonal split
Brake Fluid
Use DOT 3 in virtually all cars Never ever mix with petroleum based liquids When cleaning brake parts use only
brakeclean, clean brake fluid, or denatured alcohol
Very hygroscopic Some manufactures recommending flushing
intervals
Master cylinder
Primary piston is acted on by pushrod Secondary piston is acted on by
hydraulic pressure Each piston will have it’s own:
– Compensating port– Vent (relief) port– Return spring– Reservoir
Master cylinder diagnosis
Usually fails with one cup bypassing– Low or no fluid pressure from one side of
cylinder– Low pedal with brake light coming on
Moisture or petroleum in cylinder will destroy/swell cups
Master cylinder repairs
Rebuilding rare today Most “new” are rebuilt MUST be bench bled before installation
– If done completely system bleeding will not be necessary
Power boosters
Can be vacuum or hydraulic boosted Vacuum uses engine vacuum to assist
pedal travel Hydraulic shares power steering
pressure off of pump to assist pedal Both have fail safe if booster fails
– Fail-safe will require increased pedal effort
Vacuum booster testing
Pedal will fall away when engine started Will store vacuum for two or three
applications– If vacuum leaks off possibly check valve
leakage or internal leakage Brake fluid in booster indicates failed
master cylinder and both must be replaced
Brake hoses and lines
Steel lines are double wall Use special double flare ISO flare steel or
brass fittings– Never use single flare or compression fittings
Hoses– Usually double lined hoses– Lines on hose body should not twist when
installed
Brake hoses and lines problems
Hoses can balloon only under pressure causing spongy brakes
Inner wall can block off flow/pressure Metal lines can rust from inside out
Common hydraulic valves
Pressure differential valve Metering valve Proportioning valve
Drum brake
Duo-servo vs. non-servo Shoes
– Primary / secondary– Riveted vs. bonded– Asbestos still around
Drums– Usually cast iron– Must carry heat away
Drum brake service
Drum removal– Can be rusted around center of drum– Imports may have threaded removal holes– May need to adjust down shoes
If shoes are wet with brake fluid, oil, grease shoes must be replaced
Drums should be resurfaced All dust MUST be wetted down or vacuumed
away
Drum brake service
Shoes should be replaced one side at a time for comparison purposes
Usually remove return springs first, hold downs second
Any weak or stretched spring needs new hardware kit
Drum brake service
Adjuster should be cleaned and lubricated
Baking plate pads need lubrication Roll back dust boots for inspection Any grease or brake fluid on shoes
should be cleaned off before installation
Drum brake problems
Squealing when applied Fading Pulsating pedal
– Must isolate front or rear Snapping or clicking noise Grinding when applied Low brake pedal Locked up on very cold days
Disc brake
Two categories– Fixed– Moving
Calipers containing one or two pistons Floating caliper and sliding caliper must move
freely Rotors usually cast iron - can be vented or
solid Pads often will have wear indicators
Disc brake service
Most require R&R of calipers Slides and pins must be cleaned and lubed Some pads have anti-rattle plates or require
anti-squeak adhesive to back of pads or will have retaining tabs
As pads wear fluid level will drop Piston must be bottomed in bore DO NOT allow caliper to hang by hose
Disc brake problems
Pulsating brakes very common Binding caliper piston or slides
Drum/rotor resurface
Demo on car
Brake bleeding
Demo on car