Halderman ch097 lecture

Automotive Technology, Fourth EditionJames Halderman

BRAKE BLEEDING METHODS AND PROCEDURES

97 BRAKE BLEEDING METHODS AND PROCEDURES

ObjectivesObjectives

• The student should be able to:– Prepare to take the Brakes (A5) ASE

certification test content area “A” (Hydraulic System Diagnosis and Repair).

– Explain how to bench bleed a master cylinder.

– Describe the proper brake bleeding sequence.

– Describe the single stroke manual brake bleeding procedure.

ObjectivesObjectives

• The student should be able to:– Discuss how to gravity bleed the hydraulic

brake system. – List the steps needed to perform a pressure

bleed procedure. – Discuss how to vacuum bleed a hydraulic

brake system.

BRAKE BLEEDINGBRAKE BLEEDING

Brake BleedingBrake Bleeding

• The Need for Brake Bleeding– Brake bleeding is removing trapped air

from hydraulic system– Air in hydraulic system results in “spongy”

brakes

• The Need for Brake Bleeding– Brake pedal will travel farther than usual

before engaging– Air gets into system when brake line or unit

is opened

• The Need for Brake Bleeding– Air gets into system through poor

connections or holes in lines– Absorption of moisture into fluid can result

in air

• Bench Bleeding the Master Cylinder– Master cylinder located at highest section

of braking system– Some master cylinders have bleeder valves

• Bench Bleeding the Master Cylinder– If no bleeder valve, loosen brake line

fittings at master cylinder– Bleed master cylinder on the bench before

installing

Figure 97-1 Bench bleeding a master cylinder. Always clamp a master cylinder in a vise by the mounting flange to prevent distortion of the cylinder bore. Bench bleeding tubes can also be used that route the fluid back into the reservoir.

• On-Vehicle Master Cylinder Bleeding– STEP 1: Fill master cylinder with brake fluid.

• Use fluid from sealed container• Fill to full level

• On-Vehicle Master Cylinder Bleeding– STEP 2: Have assistant slowly depress

brake pedal as you open master cylinder bleed screw.

• Important: bleed primary section of master cylinder first

• On-Vehicle Master Cylinder Bleeding– STEP 2: Have assistant slowly depress

brake pedal as you open master cylinder bleed screw.

• Before brake pedal reaches floor, close bleeder valve

• NOTE: A proper manual bleeding of the hydraulic system requires that accurate communications occur between the person depressing the brake pedal and the person opening and closing the bleeder valve(s). The bleeder valve (also called bleed valve) should be open only when the brake pedal is being depressed.

• NOTE: The valve must be closed when the brake pedal is released to prevent air from being drawn into the system.

• On-Vehicle Master Cylinder Bleeding– STEP 3: Repeat procedure several times.

• Solid flow of brake fluid should be seen

• On-Vehicle Master Cylinder Bleeding– STEP 3: Repeat procedure several times.

• If cylinder lacks bleeder valve, loosen outlet tube nuts

BRAKE BRAKE BLEEDER VALVEBLEEDER VALVE

LOOSENING METHODSLOOSENING METHODS

Brake Bleeder Valve Loosening Brake Bleeder Valve Loosening MethodsMethods

• Opening bleeder valve can cause sheering off of valve

• Bleeder valves are tapered• Can become wedged in caliper

Figure 97-2 Typical bleeder valve from a disc brake caliper. The arrows point to the taper section that does the actual sealing. It is this taper that requires a shock to loosen. If the bleeder is simply turned with a wrench, the bleeder usually breaks off because the tapered part at the bottom remains adhered to the caliper or wheel cylinder. Once loosened, brake fluid flows around the taper and out through the hole in the side of the bleeder valve. The hole is clogged in this example and needs to be cleaned out.

Figure 97-3 Typical bleeder locations. Note that the combination valve and master cylinder shown do not have bleeder valves; therefore, bleeding is accomplished by loosening the brake line at the outlet ports.

• Several methods to loosen stuck valves• Hit and Tap Method

– STEP 1: Apply penetrating oil to lubricate threads.

• Tap on end of bleeder valve with steel hammer

– STEP 2: Using a 6-point wrench or socket, tap valve in clockwise direction (tighten).

– STEP 3: Using 6-point wrench or socket, tap valve counter-clockwise to loose and remove.

• NOTE: It is the shock of the tap on the wrench that breaks loose the bleeder valve. Simply pulling on the wrench often results in breaking off the bleeder.

– STEP 4: If valve still frozen, repeat Steps 1 through 3.

• Air Punch Method– Apply penetrating oil– Use air punch near bleeder valve– Simultaneously, try to loosen valve

Figure 97-4 Using an air punch next to the bleeder valve to help “break the taper” on the bleeder valve.

• Heat and Tap Method– Heat area around bleeder valve with torch– Heat expands size of hole

• Heat and Tap Method– Usually bleeder can be loosened and

removed– Try turning valve clockwise (tighten) first

before turning counter-clockwise to loosen

• Heat and Tap Method– CAUTION: The heat from a torch will

damage the rubber seals inside the caliper or wheel cylinder. Using heat to free a stuck bleeder valve will require that all internal rubber parts be replaced.

• Wax Method– STEP 1: Heat bleeder valve with torch.

• Heat causes valve to expand

• Wax Method– STEP 2: Remove heat from valve.

• As valve cools, touch paraffin or candle wax to hot valve

• Wax will melt and enter threads

• Wax Method– STEP 3: Allow bleeder to cool until it can be

touched.• Wax should be returned to solid form • Cooled wax lubricates threads

• Wax Method– STEP 3: Allow bleeder to cool until it can be

touched.• Try turning valve clockwise (tighten) first

before turning counter-clockwise to loosen

BLEEDING SEQUENCEBLEEDING SEQUENCE

Bleeding SequenceBleeding Sequence

• Bleeding Sequence– Bleed master cylinder first– Then bleed combination valve, if equipped

• Bleeding Sequence– Check master cylinder frequently; do not

allow to run dry– Start bleeding with wheel farthest from

master cylinder– Work toward wheel closest to master

cylinder

• Bleeding Sequence– Sequence for most vehicles

1. Right rear2. Left rear

• Bleeding Sequence– Sequence for most vehicles

3. Right front4. Left front

Figure 97-5 Most vehicle manufacturers recommend starting the brake bleeding process at the rear wheel farthest from the master cylinder.

• Bleeding Sequence– NOTE: If the vehicle has two wheel

cylinders on one brake, bleed the upper wheel cylinder first.

• Bleeding Sequence– If vehicle has diagonal split section or ABS,

follow procedure recommended by manufacturer

• Bleeding Sequence– Two most common sequences for bleeding

brakes for diagonal-split system:• RR, LR, RF, LF

• Bleeding Sequence– Two most common sequences for bleeding

brakes for diagonal-split system:• RF, LF, RR, LR

MANUAL BLEEDINGMANUAL BLEEDING

Manual BleedingManual Bleeding

• Most commonly used method• Also called single stroke bleeding

method

• Items Needed for Manual Bleeding– Assistant to apply and release brake pedal– Bleeder screw wrench

• Items Needed for Manual Bleeding– Two feet of clear, plastic hose; small

enough to fit snugly over bleeder screws– Clean jar partially filled with clean brake

• Manual Bleeding Procedure– STEP 1: Discharge vacuum or hydraulic

power booster (if equipped) by pumping brakes with ignition off.

• Pump until pedal feels hard

• Manual Bleeding Procedure– STEP 2: Fill master cylinder reservoir.

• Make sure it is at least half full throughout procedure

• Manual Bleeding Procedure– STEP 3: Attach plastic hose to bleeder

screw of fist wheel cylinder.• Submerge end of tube in jar of brake fluid

Figure 97-6 Bleeding brakes using clear plastic tubing makes it easy to see air bubbles. Submerging the hose in a container of clean brake fluid helps ensure that all of the air will be purged by the system.

• Manual Bleeding Procedure– STEP 4: Have assistant apply brake slowly

and lightly.• Open bleeder valve one-half turn

• Manual Bleeding Procedure– STEP 5: Tighten bleeder screw.

• Have assistant slowly release brake pedal

• Manual Bleeding Procedure– STEP 6: Wait at least 15 seconds to allow

tiny bubbles to form larger bubbles.

• Manual Bleeding Procedure– STEP 7: Repeat steps 4 and 5 until no more

air bubbles emerge.– STEP 8: Transfer plastic hose to bleeder

screw of next wheel cylinder.• Repeat steps 4 through 7

• Manual Bleeding Procedure– STEP 8: Transfer plastic hose to bleeder

screw of next wheel cylinder.• Continue around vehicle until all brakes

have been bled

VACUUM BLEEDINGVACUUM BLEEDING

Vacuum BleedingVacuum Bleeding

• Uses special suction pump that attaches to bleeder screw

• Advantages of Vacuum Bleeding– Requires only one technician– Easy and equipment is inexpensive

• Disadvantages of Vacuum Bleeding– Vacuum tool must be used– Air can be drawn into line between bleeder

valve and hose, creating bubbles– Bubbles can be interpreted as air in system

• Vacuum Bleeding Procedure– STEP 1: Fill master cylinder with new brake

fluid.• Make sure cylinder remains at least half full

throughout procedure

– STEP 2: Attach plastic tube from vacuum bleeder to bleeder screw of first wheel cylinder.

Figure 97-7 Using a compressed air-powered vacuum bleeder.

Figure 97-8 Vacuum bleeding uses atmospheric pressure to force brake fluid through the hydraulic system.

• Vacuum Bleeding Procedure– STEP 3: Operate the bleeder to create

partial vacuum in catch bottle.– STEP 4: Loosen bleeder screw

approximately one-half turn.• Brake fluid and bubbles will flow into bottle

• Vacuum Bleeding Procedure– STEP 4: Loosen bleeder screw

approximately one-half turn.• When fluid is free of bubbles, tighten

bleeder screw

• Vacuum Bleeding Procedure– STEP 5: Repeat steps 3 and 4 until no more

air bubbles emerge from bleeder.

• Vacuum Bleeding Procedure– STEP 6: Transfer the vacuum bleeder to the

next wheel cylinder or caliper in bleeding sequence.

• Repeat steps 3 and 4

GRAVITY BLEEDINGGRAVITY BLEEDING

Gravity BleedingGravity Bleeding

• Gravity bleeding is slow but effective• Procedure involves opening bleeder

valve and waiting until brake fluid flows from open valve

• Trapped air will rise and escape• May take several minutes before brake

fluid escapes

Figure 97-9 Gravity bleeding is simply opening the bleeder valve and allowing gravity to force the brake fluid out of the bleeder valve. Because air is lighter than brake fluid all of the air escapes before the brake fluid runs out.

• Advantages of Gravity Bleeding– All four brakes can be bled simultaneously– Bleeder screws on all four wheels are

opened– System allowed to drain naturally

• Disadvantages of Gravity Bleeding– Can take an hour or more– Cannot be used on brake systems with

residual pressure check valves

• Gravity Bleeding Procedure– Equipment

• Bleeder wrench• Four lengths of plastic hose that fit over

bleeder screws• Four jars to catch dripping fluid

• Gravity Bleeding Procedure– STEP 1: Fill master cylinder reservoir with

new brake fluid.• Ensure reservoir stays at least half full

• Gravity Bleeding Procedure– STEP 2: Attach plastic tubing to each

bleeder screw.• Place ends in jars• Open each bleeder screw approximately one

full turn

bleeder screw.• Allow system to drain• Drain until fluid is free of bubbles

bleeder screw.• If no brake fluid drains out, remove valve; it

may be clogged• Do not press on brake pedal

• Gravity Bleeding Procedure– STEP 3: Close bleeder screws.

• Fill master cylinder reservoir to maximum level

PRESSURE BLEEDINGPRESSURE BLEEDING

Pressure BleedingPressure Bleeding

• Sometimes called power bleeding• Pressure bleeder attached to master

cylinder forces fluid from system

• Tools Required– Plastic hose– Jar to catch fluid– Pressure bleeder—source of air pressure

• Tools Required– Adapter to attach pressure bleeder to

master cylinder fluid reservoir– Some adapters use flat, plate-type

• Tools Required– Adapter seals against same surface as

reservoir cover• Some plastic master cylinder reservoirs

require adapters that seal against bottom of reservoir

Figure 97-10 A typical pressure bleeder. The brake fluid inside is pressurized with air pressure in the air chamber. This air pressure is applied to the brake fluid in the upper section. A rubber diaphragm separates the air from the brake fluid.

Figure 97-11 Brake fluid under pressure from the power bleeder is applied to the top of the master cylinder. It is very important that the proper adapter be used for the master cylinder. Failure to use the correct adapter or failure to release the pressure on the brake fluid before removing the adapter can cause fluid to escape under pressure.

• Metering Valve Override Tools– Metering valve override tool needed in

addition to other tools– Override tool deactivates metering valve

• Metering Valve Override Tools– Pressure of power bleeder within range

where metering valve will block fluid flow– Metering valve that requires override tool

has stem or button on one end

• Metering Valve Override Tools– To install override tool on GM vehicle,

loosen combination valve mounting bolt– Slip the slot in the tool over bolt head

• Metering Valve Override Tools– Push end of tool toward valve body until it

depresses valve plunger– Tighten mounting bolt

• Metering Valve Override Tools– Some Ford vehicles have metering valve

with stem– Stem must be pushed in to bleed front

brakes

• Metering Valve Override Tools– Ford does not have special tool– Assistant needed to override valve

• Metering Valve Override Tools– On older Chrysler and Ford vehicles, slip

one fork of tool under rubber boot– Slip other fork under valve step head

Figure 97-12 Metering valve override tool on a General Motors vehicle.

• Pressure Bleeding Procedure– STEP 1: Consult manufacturer’s

instructions.• Fill pressure bleeder with proper type of

brake fluid

• Pressure Bleeding Procedure– STEP 2: Make sure bleeder is sealed and

fluid supply valve is closed.• Use compressed air to pressurize bleeder to

about 30 PSI (207 kPa)

• Pressure Bleeding Procedure– STEP 3: Override metering valve if

necessary.

Figure 97-13 Pull-out-type metering valves being held out using a special override tool.

• Pressure Bleeding Procedure– STEP 4: Clean top of master cylinder.

• Remove master cylinder cover• Clean around gasket surface

• Pressure Bleeding Procedure– STEP 5: Fill reservoir about half full of new

brake fluid.• Install pressure bleeder adapter

• Pressure Bleeding Procedure– STEP 6: Connect pressure bleeder fluid

supply hose to adapter.– STEP 7: Open fluid supply valve on

pressure bleeder.• Check carefully for fluid leans that can

damage vehicle finish

• Pressure Bleeding Procedure– STEP 8: Slip plastic hose over bleeder

screw of first wheel cylinder or caliper.• Submerge other end in jar of brake fluid

• Pressure Bleeding Procedure– STEP 9: Open bleeder screw about one-half

turn.• Let fluid run out until air bubbles no longer

emerge

• Pressure Bleeding Procedure– STEP 10: Transfer plastic hose to bleeder

screw of next wheel cylinder.• Continue until all four wheels completed

• Pressure Bleeding Procedure– STEP 11: Remove metering override tool.– STEP 12: Close fluid supply valve on

pressure bleeder.– STEP 13: Shut off or disconnect shop air

supply before removing master cylinder adapter.

• Pressure Bleeding Procedure– STEP 14: Wrap end of fluid supply hose in

shop towel.• Disconnect from master cylinder adapter

• Pressure Bleeding Procedure– STEP 15: Remove master cylinder adapter.

• Adjust fluid level to full point• Install fluid reservoir cover

HYDRAULIC ABS HYDRAULIC ABS SERVICESERVICE

Hydraulic ABS ServiceHydraulic ABS Service

• Check Service Information– Always check service information for exact

vehicle being serviced

• Bleeding the Electric-Hydraulic Assembly– Sometimes brake pedal will feel spongy

even after four wheel cylinders have been bled

• Bleeding the Electric-Hydraulic Assembly– Air can be trapped in ABS electronic-

hydraulic (E-H) assembly– Bleeding out E-H unit purges out older

brake fluid– Use only DOT 3 brake fluid in antilock

braking system

• Bleeding the Electric-Hydraulic Assembly– CAUTION: Some ABS units require that the

brake pedal be depressed as many as 40 times to discharge brake fluid fully from the accumulator. Failure to discharge the accumulator fully can show that the brake fluid level is too low. If additional brake fluid is added, the fluid could overflow the reservoir during an ABS stop when the accumulator discharges brake fluid back into the reservoir.

• Manually Bleeding ABS Wheel Brakes– During brake service, avoid letting air enter

hydraulic system1. Do not allow brake system to run dry.

– Use brake pedal depressor or plug open brake line to keep fluid from flowing out of brake master cylinder reservoir

hydraulic system2. Check master cylinder reservoir often.

– Keep it filled with fluid

hydraulic system3. Bench bleed replacement master cylinder

to prevent introducing air into hydraulic system.

• Manually Bleeding ABS Wheel Brakes– Depress unit per manufacturer’s

recommended procedure– Bleed brakes using same procedure used

for vehicle without ABS

Figure 97-14 Special bleed valve tools are often required when bleeding some ABS units such as the Kelsey-Hayes 4WAL system.

Figure 97-15 Two bleed valve tools are needed to bleed the Kelsey-Hayes 4WAL system, which attaches to the bleeder valves on the accumulator.

• Scan Tool Bleeding– STEP 1: Check service information for

specific procedure.• Usually involves manually bleeding wheel

brakes before using scan tool

• Scan Tool Bleeding– STEP 2: Use factory scan tool or one

capable of performing automated bleed procedure.

• Scan Tool Bleeding– STEP 3: Connect scan tool to data link

connector (DLC).• Connector may be located under the dash,

in center console, or covered by a panel

Figure 97-16 To perform an automated brake bleed procedure on an antilock braking system, first connect a factory or enhanced scan tool to the data link connector (DLC) located under the dash on this vehicle.

• Scan Tool Bleeding– STEP 4: Enter vehicle information shown on

display.

Figure 97-17 Access the menu that includes antilock brake system (ABS) functions.

• Scan Tool Bleeding– STEP 5: Select ABS automated bleed from

ABS menu.– Follow instructions on scan tool

Figure 97-18 Scroll through the menus and select automated bleed procedure and follow the on-screen instructions.

BRAKE FLUIDBRAKE FLUIDREPLACEMENT/REPLACEMENT/

FLUSHINGFLUSHING

Brake Fluid Replacement/FlushingBrake Fluid Replacement/Flushing

• Flushing Procedure– Tools required

• An assistant to pump brake pedal• Bleeder screw wrench

• Flushing Procedure– Tools required

• About 2 feet of clear, plastic hose to fit over bleeder screw

• Jar partially filled with clean brake fluid

• Flushing Procedure– STEP 1: Using turkey baster, remove old

brake fluid from master cylinder reservoir.

Figure 97-19 A turkey baster can be used to remove the old brake fluid from the master cylinder reservoir. A rubber hose was attached to the end of the turkey baster to get access to the brake fluid.

• Flushing Procedure– STEP 2: Fill master cylinder reservoir with

new brake fluid.– STEP 3: Slip plastic hose over bleeder

screw of wheel cylinder to be bled.• Submerge tube in jar of brake fluid

• Flushing Procedure– STEP 4: Open bleeder screw approximately

one-half turn.– STEP 5: With bleeder screw open, have

assistant slowly depress brake pedal.

• Flushing Procedure– STEP 6: While assistant holds down brake

pedal, close bleeder screw.– STEP 7: Continue to bleed each wheel until

fluid from bleeder screw is free of discoloration and contamination.

• Flushing Procedure– STEP 8: Repeat steps 4 through 7 at each

bleeder screw in recommended sequence.– STEP 9: Check brakes for proper operation.

• Re-bleed if necessary

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