Brake Service
Chapter 58
© 2012 Delmar, Cengage Learning
Objectives
• Inspect brake systems and recommend needed
repairs
• Diagnose brake system problems
• Perform brake repairs and adjustments using
the correct materials and procedures
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Introduction and Brake
Inspection
• This chapter deals with hydraulic brake systems
– Inspection
– Diagnosis
– Repair
• Thorough inspection of the braking system
– Performed before any repairs
• Start with pedal and master cylinder
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Check Brake Pedal Feel
• Check the travel of brake pedal
– Apply foot brakes
• Should be ample amount of pedal reserve
• Pedal should feel firm, not spongy
– Spongy brake pedal indicates air or moisture in
the system
• Calling for a brake bleed
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Master Cylinder Inspection
• Fluid movement past vent port
– Should always be visible when pedal is applied
• Heavy surge from compensating port
– Indicates air in system
• Power booster: operating correctly
– Sound of air rushing into booster
• Apply the brakes
– Test brake lights
• Hydraulic safety switch service
– Brake warning lamp operates during braking
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Brake Diagnosis and Undercar
Checks
• Brakes that pull to one side
– Causes: suspension or steering systems
• Brake pedal pulsation
– Results when hydraulic pistons move during stop
– Brakes grab cause: oil or grease on lining
– Brake pull: several reasons
• Undercar checks
– Perform a visual inspection of brakes with vehicle
raised on a hoist
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Disc Brake Inspection
• Disc brakes are inspected to see that a sufficient
amount of friction material remains on pads
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Remove a front wheel and visually inspect pad
Inspect the rotor
Check rotor runout with a dial indicator
Inspect rotor thickness and brake drums
Inspect the caliper and wheel seals
Test parking brake
Inspect tubing and hoses
Check for fluid leaks
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Inspecting Drum Brake
Assemblies
• Important steps
– Remove and mark the brake drum
• Spray the flange area with penetrating oil
• Use a hammer to rap on drum
– Inspect drum brake cylinders
– Inspect drum brake linings
– Check self-adjuster operation
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Brake Fluid Service and Brake
Fluid Testing
• Correct fluid to use is listed on reservoir
– Space must be left to allow fluid expansion
• Fluid change interval
– Change fluid every two years or 30,000 miles
• Brake fluid testing methods
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Moisture content testers
Refractometer testing
Voltmeter testing
Fluid test strips
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Bleeding Brakes and
Brake Bleeding Methods
• Air or moisture in system can result in soft pedal
– Brakes are bled through a bleed screw
• Manufacturers specify bleeding sequences
• Brake bleeding methods
– Manual bleeding and manual bleeding with a hose
– Pressure bleeding and vacuum bleeding
– Reverse fluid injection and gravity bleeding
• Several problems can occur during bleeding
• Scan tool to may be required to cycle the ABS
• Avoid contamination with petroleum products
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Adjusting Brakes
• Improper brake adjustments
– Cause a low, firm pedal
• Diagnosis
– Pump pedal twice quickly to correctly diagnose
• Pedal height rises higher on second application:
brakes need adjustment
– Most brakes today have self-adjusting
mechanisms
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Master Cylinder Service and
Master Cylinder Removal
• Cover vent is obstructed
– Air can be drawn in at back of master cylinder,
aerating fluid
• Air in fluid causes a spongy pedal
– Check the vent when checking fluid level
• Removing master cylinder
– Be sure to use fender covers
– Use a vacuum brake bleeder to empty fluid from
master cylinder reservoir
• Then remove master cylinder
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Master Cylinder Disassembly
• Master cylinders
can be purchased
as new or rebuilt
– Bore of a cylinder
is corroded or
pitted: cylinder
must be replaced
• Quick take-up
master cylinders
are serviced in
the same manner
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Bench Bleeding the Master
Cylinder
• Before installing a master cylinder
– Fill with fluid and bleed air
• Quick take-up cylinder
– Casting is larger near the rear
• Pedal free travel
– Checked when master cylinder replaced
• Should be less than 1/8” of free play
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Brake Job
• Front or rear linings are replaced in pairs
– Consult the appropriate service manual
• Complete brake job includes:
– All internal hydraulic parts of wheel cylinders and
disc calipers
– New brake fluid, hardware, and springs
– Drums and rotors may be remachined on lathe
• Ethics in brake work
– Include disclaimer when incomplete brake job is
advertised
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Drum Brake Lining Removal
• Clean entire assembly before disassembling
brakes
– Brake dust is dangerous to breathe
• Low-pressure wet brake washers are the most
popular way of cleaning brake assemblies
• HEPA vacuum can also be used
• Removal of brake linings
– Requires special tools
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Rebuilding Hydraulic Cylinders
• Hydraulic wheel cylinders and disc brakes can
be rebuilt if made of cast iron and not corroded
– Two kinds of hone are available
• After honing: install new rubber parts
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Reassembling a Wheel Cylinder
and Removing Wheel Cylinders
• Reassembling a wheel cylinder
– Lips on the wheel cylinder cups face toward fluid
– Use brake fluid liberally as an assembly lubricant
• Removing wheel cylinders
– Pitted or corroded: must be replaced
– Use flare-nut wrench to remove brake tubing
fitting
– Cylinder is held to backing by two screws or clip
• Requires special service tool
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Replacing Drum Brake Shoes
• Important steps
– Clean backing plates
• Use high-temperature lubricant on pads
– Inspect brake springs
• Shoe return springs should not be loose or broken
– Service self-adjusters
• Must be installed on the correct side of the car
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Adjusting Drum Brake
Clearance
• Initial clearance adjustment
– Made before drums installed
• Brake adjusting gauge
– Adjusted to size of drum
• Star wheel of adjuster
– Turned until shoes expand to size of adjusting
gauge
• Manual adjustment
– Can be done while the drum is installed
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Drum and Rotor Service
• Drum or disc lining
are replaced
– Common practice:
remachine drums
or rotors
• Too much metal
must be
removed:
replace
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Drum Service
• Maximum amount that can be cut from most
drums is 0.060”
– Typical larger drum lists a discard diameter that
is 0.090” larger than original
• Important points
– Inspect drums to see that they are not out-ofround or scored
– Be sure there is no oil or grease on drum
– Drums and rotors can be mounted on a lathe
– Tool bit at end of the cutter is a carbide insert
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Rotor Service
• Rotor in good condition
– Provides better surface than freshly machined
• Rotors are always machined in pairs
• Machining a rotor
– Cut both sides at once, maintaining equal force
on both sides
– Newly machined surfaces must be cleaned
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On-Vehicle Rotor Machining
• On-the-car brake lathes: becoming more popular
– Before reinstalling a brake rotor: clean any rust
preventive material from surface
– Use a torque wrench when tightening lug nuts
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Disc Brake Service
• Important points
– Disc linings are usually easy to replace
– Most caliper designs require removal of caliper to
remove pads
– Before you install replacement pads in a floating
caliper, check the condition of its slides
– Open the bleed screw before retracting the
piston
– All pistons must be compressed at the same time
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Rear Disc Pad Installation and
Rebuilt Calipers
• Rear disc pad installation
– Rear-wheel disc brakes have a built-in parking
brake
– If there is a lever, do not force the piston into the
bore
• Rebuilt calipers
– Many shops find it more cost-effective to install
rebuilt calipers
• Unloaded and loaded
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Disc Caliper Rebuilding
• Major steps
– Disassemble
caliper
– Clean and inspect
caliper parts
– Inspect the pistons
– Reassembly
caliper
– Install disc pads in
the caliper
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Selecting Brake Linings
• Various lining materials are available
– Depends on application and friction
characteristics desired
• Older brake lining materials
– Classified as organic or inorganic
• Side edge of a new brake lining
– Stamped with code number established by SAE
• Aftermarket friction material certifications
– Assure aftermarket lining performance
characteristics equal to or better than new cars
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Disc Brake Noise
• Brake noise and vibration
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Most likely complaints from a customer
Important that disc linings be firmly attached
Most pads have anti-rattle clips
Metal-to-metal contact points must be lubricated
to prevent noise
– Install caliper on correct side
– Today’s linings are more fully cured but still
require some break-in
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Parking Brake Cable Service
• During a rear brake job
– Disconnect emergency brake cables from brake
linings
– Wipe off cables and apply clean grease
• Brake cable requires replacement
– Use small hose clamp to remove it from backing
plate
• Brake should be fully applied at half travel
– Follow manufacturer’s recommendations
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Vacuum Power Brake Service
• Repairs to power boosters include replacement
of the hose, filter, or check valve
• Causes of increased pedal effort
– Installation of larger diameter tires
– Defective power booster
• Vacuum booster operation test
– Exhaust all vacuum reserve from power booster
• Power brake booster problems
– Can be due to a hole in the booster diaphragm or
a stuck valve that is leaking
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Vacuum Power Brake Service
(cont’d.)
• Defective power booster
– Causes brakes to drag
• Vacuum supply checks
– Check hose that supplies vacuum to the power
booster from intake manifold
• Power brake booster problems
– Hole in booster diaphragm or a stuck valve
• Typical power boosters
– Have four studs that protrude through the
bulkhead into the passenger compartment
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Brake Warning Lamp Diagnosis
• Hydraulic safety switches
– Found on vehicles that do not have fluid level
sensing systems
• Fluid level switches
– Found on vehicles that do not have hydraulic
safety switch
• Check operation of stoplight switch
– Apply brakes and verify that stoplights come on
– Use a wiring diagram to determine how the
circuit operates
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Antilock Brake System (ABS)
System Service
• Covered in Chapter 59
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