Basic Brakes

1
Basic Brakes
2
Split systems/dual master cylinders

• Used exclusively since 1960s
• Most use front/rear split
• Some use diagonal split

3
Brake Fluid

• Fluid ruins paint!!!
• 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 recommending flushing intervals

4
Master cylinder

• Primary piston is acted on by pushrod
• Secondary piston is acted on by hydraulic
  pressure
• Each piston will have its own
• Compensating port
• Vent (relief) port
• Return spring
• Reservoir

5
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

6
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

7
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

8
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

9
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

10
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

11
Common hydraulic valves

• Pressure differential valve
• Metering valve
• Proportioning valve

12
Drum brake

• Duo-servo vs. non-servo
• Shoes
• Primary / secondary
• Riveted vs. bonded
• Asbestos still around
• Drums
• Usually cast iron
• Must carry heat away

13
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

14
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

15
Drum brake service

• Adjuster should be cleaned and lubricated
• Backing plate pads need lubrication
• Roll back dust boots for inspection
• Any grease or brake fluid on shoes should be
  cleaned off before installation

16
Drum brake problems

• Grabbing
• 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

17
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

18
Disc brake service

• Most require RR 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

19
Disc brake problems

• Pulsating brakes very common
• Binding caliper piston or slides

20
Drum/rotor resurface

• Demo on car

21
Brake bleeding

• Demo on car