This document discusses disc brake systems. It explains that the front brakes provide 75-90% of stopping power and brake systems are either diagonal or split between front and rear. It describes the master cylinder, which pressurizes brake fluid when the brake pedal is depressed. It discusses different types of brake fluid and issues with mixing fluids. It also describes common power assist units like vacuum boosters and hydroboost systems. The document outlines the components of a disc brake system and identifies two types of calipers. It lists potential issues like worn components, leaks, warping, noise, and pulling and recommends inspections or replacements to address various brake problems.

1. Disc Brake Systems
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2. Brake System Design
• The front brakes have 75-90% of the
stopping power
• Systems are split in 2 ways
– Diagonal
– Front/Rear
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3. Master Cylinder
• The master
Cylinder is bolted
to the Brake
Booster and is
located on the
bulkhead
• Pressurizes brake
fluid when service
brake pedal is
depressed
• The reservoir
holds the brake
fluid
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4. Master Cylinder
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5. Brake Fluid
• Brake fluid comes in several types
– DOT 3, 4, 5
– Most common today is Polyglycol
DOT 3 and DOT 4
– Both collect water because their
Hydroscopic
– DOT 3 Min boil point 410 dry 284 wet
– DOT 4 Min boil point 446 dry 311 wet
– DOT 5 Min boil point 500 dry 356 wet
• Silicone type should not be mixed
with 3 or 4
NEVER MIX PETROLEUM BASED
PRODUCTS WITH BRAKE
SYSTEMS!
Always add fluid
from unopened
container!
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6. Power Assist Units
• Vacuum Booster most
common
• Some cars and trucks
have HydroBoost
brake boosters
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7. Vacuum Booster
• The Vacuum Booster
is supplied vacuum
from the engine
• A “Check Valve”
keeps vacuum in
booster when engine
is off
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8. Disk Brake System
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9. Two Types of Calipers
• Fixed Caliper
– Caliper attached
directly to the knuckle
• Floating Caliper
– Caliper “Floats” on
slide pins
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10. Disk Brake System
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11. Drum and Rotor Issues
• Metal to Metal Drums and Rotors
– Friction material completely worn out
– Usually requires replacement of component
• Out of Round Drum or Warped Rotor
– Drum and Rotor can be “Turned” true
• Hot Spots or cracking
– Component should be replaced and cause of
overheat diagnosed
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12. Brake Issues
• Low, but hard brake pedal
– Worn brake shoe linings
– Misadjusted brake shoe linings
• Inspect and adjust
• Spongy brake pedal, may “pump” up
– Possible bent parts from accident
– Air in lines / calipers or wheel cylinders
• Bleed System
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13. Brake Issues
• No or Low brake pedal - LOOK OUT!!! I’m
coming through…
– Hydraulic leak in system
– Bypassing master cylinder
– Low brake fluid
• Check fluid level
• Check for leaks
• Check master cylinder
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14. Brake Issues
• Pulsating brake pedal
– Warped drums or rotors
• Machine rotors and drums
• Brake noise
– Linings worn down
– Loose parts
– Cheap brake linings
• Brake pull
– Mismatched pads
– Sticking caliper
– Alignment concerns
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