Halderman ch097 lecture

BRAKE BLEEDING METHODS AND PROCEDURES 97

Objectives 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.

Objectives 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 Bleeding The Need for Brake Bleeding Brake bleeding is removing trapped air from hydraulic system Air in hydraulic system results in “spongy” brakes

Brake Bleeding 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

Brake Bleeding 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

Brake Bleeding Bench Bleeding the Master Cylinder Master cylinder located at highest section of braking system Some master cylinders have bleeder valves

Brake Bleeding 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.

Brake Bleeding On-Vehicle Master Cylinder Bleeding STEP 1: Fill master cylinder with brake fluid. Use fluid from sealed container Fill to full level

Brake Bleeding 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

Brake Bleeding 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

Brake Bleeding 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.

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

Brake Bleeding On-Vehicle Master Cylinder Bleeding STEP 3: Repeat procedure several times. Solid flow of brake fluid should be seen

Brake Bleeding On-Vehicle Master Cylinder Bleeding STEP 3: Repeat procedure several times. If cylinder lacks bleeder valve, loosen outlet tube nuts

BRAKE BLEEDER VALVE LOOSENING METHODS

Brake Bleeder Valve Loosening Methods 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.

Brake Bleeder Valve Loosening Methods 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

Brake Bleeder Valve Loosening Methods Several methods to loosen stuck valves Hit and Tap Method STEP 2: Using a 6-point wrench or socket, tap valve in clockwise direction (tighten).

Brake Bleeder Valve Loosening Methods Several methods to loosen stuck valves Hit and Tap Method 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.

Brake Bleeder Valve Loosening Methods Several methods to loosen stuck valves Hit and Tap Method STEP 4: If valve still frozen, repeat Steps 1 through 3.

Brake Bleeder Valve Loosening Methods 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.

Brake Bleeder Valve Loosening Methods Heat and Tap Method Heat area around bleeder valve with torch Heat expands size of hole

Brake Bleeder Valve Loosening Methods Heat and Tap Method Usually bleeder can be loosened and removed Try turning valve clockwise (tighten) first before turning counter-clockwise to loosen

Brake Bleeder Valve Loosening Methods 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.

Brake Bleeder Valve Loosening Methods Wax Method STEP 1: Heat bleeder valve with torch. Heat causes valve to expand

Brake Bleeder Valve Loosening Methods 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

Brake Bleeder Valve Loosening Methods Wax Method STEP 3: Allow bleeder to cool until it can be touched. Wax should be returned to solid form Cooled wax lubricates threads

Brake Bleeder Valve Loosening Methods 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 Sequence Bleeding Sequence Bleed master cylinder first Then bleed combination valve, if equipped

Bleeding Sequence 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 Bleeding Sequence Sequence for most vehicles Right rear Left rear

Bleeding Sequence Bleeding Sequence Sequence for most vehicles Right front 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 Bleeding Sequence NOTE: If the vehicle has two wheel cylinders on one brake, bleed the upper wheel cylinder first.

Bleeding Sequence Bleeding Sequence If vehicle has diagonal split section or ABS, follow procedure recommended by manufacturer

Bleeding Sequence Bleeding Sequence Two most common sequences for bleeding brakes for diagonal-split system: RR, LR, RF, LF

Bleeding Sequence Bleeding Sequence Two most common sequences for bleeding brakes for diagonal-split system: RF, LF, RR, LR

Manual Bleeding Most commonly used method Also called single stroke bleeding method

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

Manual Bleeding 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 fluid

Manual Bleeding 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 Manual Bleeding Procedure STEP 2: Fill master cylinder reservoir. Make sure it is at least half full throughout procedure

Manual Bleeding 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 Manual Bleeding Procedure STEP 4: Have assistant apply brake slowly and lightly. Open bleeder valve one-half turn

Manual Bleeding Manual Bleeding Procedure STEP 5: Tighten bleeder screw. Have assistant slowly release brake pedal

Manual Bleeding Manual Bleeding Procedure STEP 6: Wait at least 15 seconds to allow tiny bubbles to form larger bubbles.

Manual Bleeding 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 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 Bleeding Uses special suction pump that attaches to bleeder screw Advantages of Vacuum Bleeding Requires only one technician Easy and equipment is inexpensive

Vacuum Bleeding 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 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 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 Vacuum Bleeding Procedure STEP 4: Loosen bleeder screw approximately one-half turn. When fluid is free of bubbles, tighten bleeder screw

Vacuum Bleeding Vacuum Bleeding Procedure STEP 5: Repeat steps 3 and 4 until no more air bubbles emerge from bleeder.

Vacuum Bleeding 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 Bleeding Gravity bleeding is slow but effective Procedure involves opening bleeder valve and waiting until brake fluid flows from open valve

Gravity Bleeding 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.

Gravity Bleeding Advantages of Gravity Bleeding All four brakes can be bled simultaneously Bleeder screws on all four wheels are opened System allowed to drain naturally

Gravity Bleeding Disadvantages of Gravity Bleeding Can take an hour or more Cannot be used on brake systems with residual pressure check valves

Gravity Bleeding Gravity Bleeding Procedure Equipment Bleeder wrench Four lengths of plastic hose that fit over bleeder screws Four jars to catch dripping fluid

Gravity Bleeding Gravity Bleeding Procedure STEP 1: Fill master cylinder reservoir with new brake fluid. Ensure reservoir stays at least half full

Gravity Bleeding Gravity Bleeding Procedure STEP 2: Attach plastic tubing to each bleeder screw. Place ends in jars Open each bleeder screw approximately one full turn

Gravity Bleeding Gravity Bleeding Procedure STEP 2: Attach plastic tubing to each bleeder screw. Allow system to drain Drain until fluid is free of bubbles

Gravity Bleeding Gravity Bleeding Procedure STEP 2: Attach plastic tubing to each bleeder screw. If no brake fluid drains out, remove valve; it may be clogged Do not press on brake pedal

Gravity Bleeding Gravity Bleeding Procedure STEP 3: Close bleeder screws. Fill master cylinder reservoir to maximum level

Pressure Bleeding Sometimes called power bleeding Pressure bleeder attached to master cylinder forces fluid from system

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

Pressure Bleeding Tools Required Adapter to attach pressure bleeder to master cylinder fluid reservoir Some adapters use flat, plate-type

Pressure Bleeding 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.

Pressure Bleeding Metering Valve Override Tools Metering valve override tool needed in addition to other tools Override tool deactivates metering valve

Pressure Bleeding 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

Pressure Bleeding 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

Pressure Bleeding Metering Valve Override Tools Push end of tool toward valve body until it depresses valve plunger Tighten mounting bolt

Pressure Bleeding Metering Valve Override Tools Some Ford vehicles have metering valve with stem Stem must be pushed in to bleed front brakes

Pressure Bleeding Metering Valve Override Tools Ford does not have special tool Assistant needed to override valve

Pressure Bleeding 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 Pressure Bleeding Procedure STEP 1: Consult manufacturer’s instructions. Fill pressure bleeder with proper type of brake fluid

Pressure Bleeding 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 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 Pressure Bleeding Procedure STEP 4: Clean top of master cylinder. Remove master cylinder cover Clean around gasket surface

Pressure Bleeding Pressure Bleeding Procedure STEP 5: Fill reservoir about half full of new brake fluid. Install pressure bleeder adapter

Pressure Bleeding 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 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 Pressure Bleeding Procedure STEP 9: Open bleeder screw about one-half turn. Let fluid run out until air bubbles no longer emerge

Pressure Bleeding Pressure Bleeding Procedure STEP 10: Transfer plastic hose to bleeder screw of next wheel cylinder. Continue until all four wheels completed

Pressure Bleeding 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 Pressure Bleeding Procedure STEP 14: Wrap end of fluid supply hose in shop towel. Disconnect from master cylinder adapter

Pressure Bleeding Pressure Bleeding Procedure STEP 15: Remove master cylinder adapter. Adjust fluid level to full point Install fluid reservoir cover

Hydraulic ABS Service Check Service Information Always check service information for exact vehicle being serviced

Hydraulic ABS Service Bleeding the Electric-Hydraulic Assembly Sometimes brake pedal will feel spongy even after four wheel cylinders have been bled

Hydraulic ABS Service 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

Hydraulic ABS Service 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.

Hydraulic ABS Service Manually Bleeding ABS Wheel Brakes During brake service, avoid letting air enter hydraulic system 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 ABS Service Manually Bleeding ABS Wheel Brakes During brake service, avoid letting air enter hydraulic system Check master cylinder reservoir often. Keep it filled with fluid

Hydraulic ABS Service Manually Bleeding ABS Wheel Brakes During brake service, avoid letting air enter hydraulic system Bench bleed replacement master cylinder to prevent introducing air into hydraulic system.

Hydraulic ABS Service 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.

Hydraulic ABS Service Scan Tool Bleeding STEP 1: Check service information for specific procedure. Usually involves manually bleeding wheel brakes before using scan tool

Hydraulic ABS Service Scan Tool Bleeding STEP 2: Use factory scan tool or one capable of performing automated bleed procedure.

Hydraulic ABS Service 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.

Hydraulic ABS Service Scan Tool Bleeding STEP 4: Enter vehicle information shown on display.

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

Hydraulic ABS Service 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 FLUID REPLACEMENT/ FLUSHING

Brake Fluid Replacement/Flushing Flushing Procedure Tools required An assistant to pump brake pedal Bleeder screw wrench

Brake Fluid Replacement/Flushing Flushing Procedure Tools required About 2 feet of clear, plastic hose to fit over bleeder screw Jar partially filled with clean brake fluid

Brake Fluid Replacement/Flushing 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.

Brake Fluid Replacement/Flushing 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

Brake Fluid Replacement/Flushing Flushing Procedure STEP 4: Open bleeder screw approximately one-half turn. STEP 5: With bleeder screw open, have assistant slowly depress brake pedal.

Brake Fluid Replacement/Flushing 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.

Brake Fluid Replacement/Flushing 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

TECH TIP Check That All Bleeder Valves Are Pointing Up Make certain all the brake components such as calipers and wheel cylinders are correctly installed with the bleeder valve located on the highest section of the part. Some wheel cylinders and calipers (such as many Ford calipers) can be installed upside down! BACK TO PRESENTATION This usually occurs whenever both front calipers are off the vehicle and they accidentally get reversed left to right. If this occurs, the air will never be completely bled from the caliper.

TECH TIP Tiny Bubbles Do not use excessive brake pedal force while bleeding and never bleed the brake with the engine running! The extra assist from the power brake unit greatly increases the force exerted on the brake fluid in the master cylinder. The trapped air bubbles may be dispersed into tiny bubbles that often cling to the inside surface of the brake lines. BACK TO PRESENTATION These tiny air bubbles may not be able to be bled from the hydraulic system until enough time has allowed the bubbles to re-form. If the dispersal of the air into tiny bubbles is suspected, try tapping the calipers or wheel cylinders with a plastic hammer. After this tapping, simply waiting for a period of time will cause the bubbles to reform into larger and easier-to-bleed air pockets. Most brake experts recommend waiting 15 seconds or longer between attempts to bleed each wheel. This waiting period is critical and allows time for the air bubbles to form. NOTE: To help prevent depressing the brake pedal down too far, some experts recommend placing a 2 x 4 in. board under the brake pedal. This helps prevent the seals inside the master cylinder from traveling over unused sections inside the bore that may be corroded or rusty.

TECH TIP The Master Cylinder One-Drip-Per-Second Test Excessive brake wear is often caused by misadjusted brake linkage or brake light switches keeping the brake pedal from fully releasing. If the brake pedal is not fully released, the primary piston sealing cup blocks the compensating port from the brake fluid reservoir. BACK TO PRESENTATION To test if this is the problem, loosen both lines from the master cylinder. Brake fluid should drip out of both lines about one drip per second. This is why this test is also called the “Master Cylinder Drip Test.” If the master cylinder does not drip, the brake pedal may not be allowing the master cylinder to fully release. Have an assistant pull up on the brake pedal. If the dripping starts, the problem is due to a misadjusted brake light or speed (cruise) control switch or pedal stop. If the master cylinder still does not drip, loosen the master cylinder from the power booster. If the master cylinder now starts to drip, the pushrod adjustment is too long. If the master cylinder still does not drip, the problem is in the master cylinder itself. Check for brake fluid contamination. If mineral oil, such as engine oil, power steering fluid, or automatic transmission fluid (ATF), has been used in the system, the rubber sealing cups swell and can block off the compensating port. If contamination is discovered, every brake component that contains rubber must be replaced.

TECH TIP ABS Bleeding Made Easy To avoid having to bleed the hydraulic unit, use a brake pedal depressor during brake service to avoid losing brake fluid. This simple precaution keeps air from getting into the hard-to-bleed passages of the hydraulic unit. BACK TO PRESENTATION

Halderman ch097 lecture

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