basic brakes. split systems/dual master cylinders s used exclusively since 1960s s most use...

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