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  • Figure 96-1 Brake fluid can absorb moisture from the air even through plastic, so many experts recommend that brake fluid be purchased in metal containers, if possible.
  • Figure 96-2 Brake fluid absorbs moisture from the air at the rate of about 2% per year. As the brake fluid absorbs water, its boiling temperature decreases.
  • Figure 96-3 DOT 5 brake fluid is used mostly in motorcycles because if spilled, it will not hurt painted surfaces.
  • Figure 96-5 If the brake fluid is black in color, it should be replaced.
  • Figure 96-6 (a) A brake fluid test strip is being used to test the condition of the brake fluid.
  • Figure 96-6 (b) The color of the test strip is then compared with a chart on the package, which indicates the condition and if the fluid should be replaced.
  • Figure 96-7 An electronic tester that measures the boiling temperature of the brake fluid is useful to help determine if the brake fluid needs to be replaced.
  • CHART 96–1 Notice that if a rubber is OK to use for brake fluid it is not OK to use for oil or grease.
  • Figure 96-8 The master cylinder piston seals are usually constructed from EPDM rubber, and the diaphragm of the vacuum power brake booster is usually made from SBR.
  • Figure 96-9 Cross-sectional view of a typical drum brake wheel cylinder. Most wheel cylinder boots and cups are either SBR or EPDM rubber.
  • Figure 96-10 Exploded view of a typical disc brake caliper. Both the caliper seal and dust boot are constructed of EPDM rubber.
  • Figure 96-11 Steel brake tubing is double-walled for strength and plated for corrosion resistance.
  • Figure 96-12 An SAE flare brake line fitting. Because of the slight difference in flare angle, double-flare fitting seals cause a wedging action.
  • Figure 96-13 An ISO fitting, also called a bubble or ball-type flare.
  • Figure 96-14 A tubing cutter is the preferred tool to use to cut brake line because it leaves a clean edge.
  • Figure 96-15 (a) Double flaring the end of a brake line. (a) Clamp the line at the correct height above the surface of the clamping tool using the shoulder of the insert as a gauge.
  • Figure 96-15 (b) Double flaring the end of a brake line. (b) The insert is pressed into the end of the tubing. This creates the first bend.
  • Figure 96-15 (c) Double flaring the end of a brake line. (c) Remove the insert and use the pointed tool to complete the overlap double flare.
  • Figure 96-15 (d) Double flaring the end of a brake line. (d) The completed operation as it appears while still in the clamp.
  • Figure 96-16 (a) Making an ISO flare requires a special tool. (a) Position the brake line into the two-part tool at the correct height using the gauge end of the tool.
  • Figure 96-16 (b) Making an ISO flare requires a special tool. (b) Assemble the two blocks of the tool together and clamp in a vise. Turn the tool around and thread it into the tool block. The end of the threaded part of the tool forms the “bubble” or ISO flare.
  • Figure 96-17 Whenever disconnecting or tightening a brake line, always use the correct size flare-nut wrench. A flare-nut wrench is also called a tube-nut wrench or a line wrench.
  • Figure 96-18 The coils in the brake line help prevent cracks caused by vibration.
  • Figure 96-19 Armored brake line is usually used in the location where the line may be exposed to rock or road debris damage. Even armored brake line can leak and a visual inspection is an important part of any brake service.
  • Figure 96-21 Flexible brake hoses are used between the frame or body of the vehicle and the wheel brakes. Because of suspension and/or steering movement, these flexible brake lines must be strong enough to handle high brake fluid pressures, yet remain flexible. Note that this flexible brake hose is further protected against road debris with a plastic conduit covering.
  • Figure 96-22 (a) Typical flexible brake hose showing the multiple layers of rubber and fabric.
  • Figure 96-22 (b) The inside diameter (ID) is printed on the hose (3 mm).
  • Figure 96-23 Brake hose fabric being woven at the factory.
  • Figure 96-24 Typical flexible brake hose faults. Many faults cannot be seen, yet can cause the brakes to remain applied after the brake pedal is released.
  • Figure 96-25 Flexible brake hose should be carefully inspected for cuts or other damage, especially near sections where the brake hose is attached to the vehicle. Notice the crack and cut hose next to the mounting bracket.

Transcript

  • 1. BRAKE FLUID AND LINES 96
  • 2. Objectives
    • The student should be able to:
      • Prepare for the Brakes (A5) ASE certification test.
      • List the types of brake fluids.
      • Describe where armored brake line is used.
      • Discuss the differences between double-flare and ISO flare.
      • Explain how flexible brake lines should be handled during service.
  • 3. Objectives
    • The student should be able to:
      • List the precautions necessary when handling or disposing of brake fluid.
      • Discuss the types of rubber that are used in brake system components.
  • 4. BRAKE FLUID
  • 5. Brake Fluid
    • Brake fluid is designed to function in the hydraulic brake system under all operating conditions
    • Boiling point is one of the most critical aspects and ratings for brake fluid
    • Brake fluid should be changed regularly as part of normal routine service
  • 6. Brake Fluid
    • All brake fluids must be able to pass tests for the following:
      • Fluidity at low temperatures.
      • Controlled percentage loss due to evaporation at high temperatures (tested at 212°F [100°C]).
  • 7. Brake Fluid
    • All brake fluids must be able to pass tests for the following:
      • Compatibility with other brake fluids.
      • Resistance to oxidation.
  • 8. Brake Fluid
    • All brake fluids must be able to pass tests for the following:
      • Specific effects on rubber, including:
        • No disintegration
  • 9. Brake Fluid
    • All brake fluids must be able to pass tests for the following:
      • Specific effects on rubber, including:
        • No increase in hardness of the rubber tested
  • 10. Brake Fluid
    • All brake fluids must be able to pass tests for the following:
      • Specific effects on rubber, including:
        • Limited amount of decrease in hardness of the rubber
  • 11. Brake Fluid
    • Physical Properties
      • Brake fluid is a polyalkylene–glycol–ether mixture called polyglycol
      • Polyglycol brake fluid is clear to amber in color
  • 12. Brake Fluid
    • Physical Properties
      • Brake fluid has to have the following characteristics:
        • A high boiling point
  • 13. Brake Fluid
    • Physical Properties
      • Brake fluid has to have the following characteristics:
        • A low freezing point
  • 14. Brake Fluid
    • Physical Properties
      • Brake fluid has to have the following characteristics:
        • Ability to not damage rubber parts in the brake system
  • 15. Brake Fluid
    • Brake Fluid Specifications
      • All brake fluid must meet Federal Motor Vehicle Safety Standard (FMVSS) 116
      • The SAE the DOT have established brake fluid specification standards as shown in the following chart
  • 16. DOT Brake Fluid Specifications
  • 17. Brake Fluid
    • The wet boiling point is often called “equilibrium reflux boiling point” (ERBP)
    • ERBP refers to the method in the specification (SAE J1703) by which the fluid is exposed to moisture and tested
  • 18. Brake Fluid
    • Brake Fluid Specifications
      • DOT 3
        • DOT 3 brake fluid is the type most often used
  • 19. Brake Fluid
    • Brake Fluid Specifications
      • DOT 3
        • DOT 3 brake fluid has some important characteristics including:
          • It absorbs moisture. According to the Society of Automotive Engineers (SAE), DOT 3 can absorb 2% of its volume in water per year.
  • 20. Brake Fluid
    • Brake Fluid Specifications
      • DOT 3
        • DOT 3 brake fluid has some important characteristics including:
          • DOT 3 must be used from a sealed (capped) container. If left open for any length of time, DOT 3 will absorb moisture from the surrounding air, which is called hygroscopic.
  • 21. Brake Fluid
    • Brake Fluid Specifications
      • DOT 3
        • DOT 3 brake fluid has some important characteristics including:
          • Always check the brake fluid recommendations on the top of the master cylinders of imported vehicles before adding DOT 3.
  • 22. Brake Fluid
    • Brake Fluid Specifications
      • CAUTION: DOT 3 brake fluid is a very strong solvent and can remove paint! Care is required when working with DOT 3 brake fluid to avoid contact with the vehicle’s painted surfaces. It also takes the color out of leather shoes.
  • 23. Figure 96-1 Brake fluid can absorb moisture from the air even through plastic, so many experts recommend that brake fluid be purchased in metal containers, if possible.
  • 24. Figure 96-2 Brake fluid absorbs moisture from the air at the rate of about 2% per year. As the brake fluid absorbs water, its boiling temperature decreases.
  • 25. Brake Fluid
    • Brake Fluid Specifications
      • DOT 4
        • DOT 4 brake fluid is formulated for use by all vehicles, that are designed to use DOT 3.
  • 26. Brake Fluid
    • Brake Fluid Specifications
      • DOT 4
        • DOT 4 is polyglycol based with added borate esters to provide an extra buffer for the fluid against acids that can form in the moisture that has been absorbed in the fluid when it is heated.
  • 27. Brake Fluid
    • Brake Fluid Specifications
      • DOT 4
        • Some vehicle manufacturers recommend that DOT 3 and DOT 4 not be mixed.
  • 28. Brake Fluid
    • Brake Fluid Specifications
      • DOT 4
        • If DOT 4 is to be used, the system should be purged of all of the old DOT 3 and replaced with DOT 4.
  • 29. Brake Fluid
    • Brake Fluid Specifications
      • NOTE: Because brake fluid absorbs moisture over time, many vehicle manufacturers recommend changing the brake fluid as part of the standard services to be performed routinely. The typical recommended brake fluid change interval is every two years or every 30,000 miles (48,000 km), whichever comes first.
  • 30. Brake Fluid
    • Brake Fluid Specifications
      • NOTE: This is particularly important for vehicles equipped with an antilock braking system (ABS) because of the problem of expensive brake component wear or corrosion caused by contaminated brake fluid.
    ?
  • 31. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5.1
        • DOT 5.1 brake fluid is a non-silicone-based polyglycol fluid and is clear to amber in color.
  • 32. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5.1
        • DOT 5.1 can be mixed with either DOT 3 or DOT 4 according to brake fluid manufacturers’ recommendations.
  • 33. Brake Fluid
    • Brake Fluid Specifications
      • CAUTION: Some vehicle manufacturers such as Chrysler do not recommend the use of or the mixing of other types of polyglycol brake fluid and specify the use of DOT 3 brake fluid only. Always follow the vehicle manufacturer’s recommendation.
  • 34. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • DOT 5 brake fluid, commonly called silicone brake fluid, is made from polydimethylsiloxanes.
  • 35. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • DOT 5 brake fluid is purple (violet) in color.
  • 36. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • It is called nonhygroscopic because it does not absorb any water.
  • 37. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • DOT 5 is tested using standardized SAE procedures in a humidity chamber.
  • 38. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • Silicones have about three times the amount of dissolved air as glycol fluids, which causes concern about its use
          • Silicone brake fluid has an affinity for air; therefore, it is more difficult to bleed the hydraulic system of trapped air.
  • 39. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • Silicones have about three times the amount of dissolved air as glycol fluids, which causes concern about its use
          • The trapped air expands with increasing temperature, causing the brake pedal to feel “mushy.”
  • 40. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • Silicones have about three times the amount of dissolved air as glycol fluids, which causes concern about its use
          • The air trapped in the silicone brake fluid can also “off-gas” at high altitudes, causing a mushy brake pedal and reduced braking performance.
  • 41. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • Silicones have about three times the amount of dissolved air as glycol fluids, which causes concern about its use
          • DOT 5 brake fluid should not be mixed with any other type of brake fluid. Therefore, the entire braking system must be completely flushed and refilled with DOT 5.
  • 42. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • Silicones have about three times the amount of dissolved air as glycol fluids, which causes concern about its use
          • DOT 5 does not affect rubber parts and will not cause corrosion.
  • 43. Brake Fluid
    • Brake Fluid Specifications
      • DOT 5
        • Silicones have about three times the amount of dissolved air as glycol fluids, which causes concern about its use
          • DOT 5 is expensive. It is approximately four times the cost of DOT 3 brake fluid.
  • 44. Brake Fluid
    • Brake Fluid Specifications
      • NOTE: The characteristic of DOT 5 silicone brake fluid to absorb air is one of the major reasons why it is not recommended for use with an antilock braking system (ABS). In an ABS, valves and pumps are used which can aerate the brake fluid. Brake fluid filled with air bubbles cannot properly lubricate the ABS components and will cause a low, soft brake pedal.
  • 45. Figure 96-3 DOT 5 brake fluid is used mostly in motorcycles because if spilled, it will not hurt painted surfaces.
  • 46. Brake Fluid
    • Brake Fluid Inspection and Testing
      • The brake fluid should be inspected regularly, including the following items:
        • Proper level: Brake fluid level should be above the minimum level (labeled MIN) and below the maximum (labeled MAX) on the side of the master cylinder reservoir.
  • 47. Brake Fluid
    • Brake Fluid Inspection and Testing
      • The brake fluid should be inspected regularly, including the following items:
        • Color/condition: New brake fluid is clear or amber in color. Discolored fluid should be changed.
  • 48. Brake Fluid
    • Brake Fluid Inspection and Testing
      • The brake fluid should be inspected regularly, including the following items:
        • Tested using a tester or test strips: Test strips can be used to measure copper ions that increase as the brake fluid becomes deteriorated.
  • 49. Brake Fluid
    • Brake Fluid Inspection and Testing
      • The brake fluid should be inspected regularly, including the following items:
        • Boiling point tester: An electronic tester can be used to measure the actual boiling temperature of the brake fluid.
  • 50. Brake Fluid
    • Brake Fluid Inspection and Testing
      • The brake fluid should be inspected regularly, including the following items:
        • Brake fluid contamination test: To check the brake fluid, use a Styrofoam cup filled with water.
          • Place a teaspoon (1 ml) of brake fluid from the master cylinder into the water.
  • 51. Brake Fluid
    • Brake Fluid Inspection and Testing
      • The brake fluid should be inspected regularly, including the following items:
        • Brake fluid contamination test: To check the brake fluid, use a Styrofoam cup filled with water.
          • Pure brake fluid will completely dissolve in the water.
  • 52. Brake Fluid
    • Brake Fluid Inspection and Testing
      • The brake fluid should be inspected regularly, including the following items:
        • Brake fluid contamination test: To check the brake fluid, use a Styrofoam cup filled with water.
          • Petroleum or mineral oil fluids will float on the surface of the water, retain their color, and dissolve the Styrofoam cup at the waterline.
  • 53. Brake Fluid
    • Brake Fluid Inspection and Testing
      • The brake fluid should be inspected regularly, including the following items:
        • Brake fluid contamination test: To check the brake fluid, use a Styrofoam cup filled with water.
          • If the brake fluid is contaminated, the entire braking system must be drained and flushed and all rubber components replaced.
    ?
  • 54. Figure 96-5 If the brake fluid is black in color, it should be replaced.
  • 55. Figure 96-6 (a) A brake fluid test strip is being used to test the condition of the brake fluid.
  • 56. Figure 96-6 (b) The color of the test strip is then compared with a chart on the package, which indicates the condition and if the fluid should be replaced.
  • 57. Figure 96-7 An electronic tester that measures the boiling temperature of the brake fluid is useful to help determine if the brake fluid needs to be replaced.
  • 58. BRAKE FLUID SERVICE PROCEDURES AND PRECAUTIONS
  • 59. Brake Fluid Service Procedures and Precautions
    • Store brake fluid in its original container.
      • Purchase brake fluid in small containers
      • Keep all brake fluid containers tightly closed
  • 60. Brake Fluid Service Procedures and Precautions
    • Remove any dirt, moisture, or other contamination from the top and outside of the container before opening.
    • Always discard empty brake fluid containers. Never use them for anything except brake fluid.
  • 61. Brake Fluid Service Procedures and Precautions
    • Do not transfer brake fluid to any other container that may have contained oil, kerosene, gasoline, antifreeze, water, cleaners, or any other liquids or chemicals.
  • 62. Brake Fluid Service Procedures and Precautions
    • Do not reuse brake fluid that has been siphoned from another vehicle or drawn out during a brake bleeding operation. (Brake bleeding means to open special bleeder valves in the hydraulic system to rid the system of any trapped air.)
    • Use only fresh, new brake fluid for flushing the hydraulic brake system.
  • 63. Brake Fluid Service Procedures and Precautions
    • CAUTION: Alcohol or flushing fluids should not be used because they cannot be totally removed from a closed hydraulic brake system and will contaminate the system. Disassembled parts, however, can and should be cleaned with denatured alcohol or spray brake cleaner where the parts can be visually inspected to be free of cleaning solutions.
  • 64. Brake Fluid Service Procedures and Precautions
    • Brake Fluid Handling and Disposal
      • Protective clothing and safety glasses or goggles should be worn
      • Brake fluid becomes a hazardous waste if spilled onto open ground, where it can seep into groundwater
  • 65. Brake Fluid Service Procedures and Precautions
    • Brake Fluid Handling and Disposal
      • The disposal requirements for brake fluid spilled onto open ground vary with the exact amount spilled and other factors
      • Refer to local EPA guidelines and requirements for the exact rules and regulations in your area
  • 66. RUBBER TYPES
  • 67. Rubber Types
    • Rubber products are called elastomers
    • Some are oil- and grease-resistant and can be harmed by brake fluid, while others are brake-fluid resistant and can swell or expand if they come in contact with oil or grease (this swelling is necessary for the seals to withstand high hydraulic pressures)
  • 68. Rubber Types
    • Silicone (DOT 5) brake fluid does not cause rubber to swell; therefore, a rubber swell additive is used (the additive can cause SBR rubber to swell too much)
  • 69. CHART 96–1 Notice that if a rubber is OK to use for brake fluid it is not OK to use for oil or grease.
  • 70. Figure 96-8 The master cylinder piston seals are usually constructed from EPDM rubber, and the diaphragm of the vacuum power brake booster is usually made from SBR.
  • 71. Figure 96-9 Cross-sectional view of a typical drum brake wheel cylinder. Most wheel cylinder boots and cups are either SBR or EPDM rubber.
  • 72. Figure 96-10 Exploded view of a typical disc brake caliper. Both the caliper seal and dust boot are constructed of EPDM rubber.
  • 73. Brake Lines
    • Terminology
      • Steel brake lines are also called brake pipes or brake tubing and are used to connect the master cylinder to each wheel
  • 74. Brake Lines
    • Terminology
      • Brake lines carry brake fluid from the master cylinder to the ABS hydraulic control unit, wheel cylinders, and brake calipers
  • 75. Brake Lines
    • Terminology
      • The brake lines contain and direct the pressure of the brake hydraulic system
  • 76. Brake Lines
    • Terminology
      • Most of the brake line consists of rigid tubing
      • For maximum strength and durability, all brake systems use double-walled brake tubing made from plated steel sheet
  • 77. Brake Lines
    • Terminology
      • There are two types of double-walled tubing:
        • Seamless
        • Multiple ply
  • 78. Brake Lines
    • Terminology
      • All double-walled tubing is plated with tin, zinc, or other similar substances for protection against rust and corrosion
  • 79. Brake Lines
    • Terminology
      • All steel brake lines have one of two basic types of ends:
        • Double Flare. This type is a 45 degree flare that meets SAE standard J533 also called an SAE flare)
  • 80. Brake Lines
    • Terminology
      • All steel brake lines have one of two basic types of ends:
        • ISO, which means International Standards Organization (also called a ball flare or bubble flare)
  • 81. Brake Lines
    • CAUTION: Copper tubing should never be used for brake lines. Copper tends to burst at a lower pressure than steel.
  • 82. Figure 96-11 Steel brake tubing is double-walled for strength and plated for corrosion resistance.
  • 83. Figure 96-12 An SAE flare brake line fitting. Because of the slight difference in flare angle, double-flare fitting seals cause a wedging action.
  • 84. Figure 96-13 An ISO fitting, also called a bubble or ball-type flare.
  • 85. Brake Lines
    • Brake Line Replacement
      • Always use a tubing cutter instead of a hacksaw to cut brake line
  • 86. Figure 96-14 A tubing cutter is the preferred tool to use to cut brake line because it leaves a clean edge.
  • 87. Brake Lines
    • Flaring Brake Line
      • When replacing steel brake line, new steel tubing should be used and a double flare or an ISO flare completed at each end using a special flaring tool
  • 88. Brake Lines
    • Flaring Brake Line
      • Always use two line wrenches to disconnect or reattach brake lines
  • 89. Brake Lines
    • CAUTION: According to vehicle manufacturers’ recommended procedures, compression fittings should never be used to join two pieces of steel brake line. Only use doubleflare ends and connections, if necessary, when replacing damaged steel brake lines.
  • 90. Figure 96-15 (a) Double flaring the end of a brake line. (a) Clamp the line at the correct height above the surface of the clamping tool using the shoulder of the insert as a gauge.
  • 91. Figure 96-15 (b) Double flaring the end of a brake line. (b) The insert is pressed into the end of the tubing. This creates the first bend.
  • 92. Figure 96-15 (c) Double flaring the end of a brake line. (c) Remove the insert and use the pointed tool to complete the overlap double flare.
  • 93. Figure 96-15 (d) Double flaring the end of a brake line. (d) The completed operation as it appears while still in the clamp.
  • 94. Figure 96-16 (a) Making an ISO flare requires a special tool. (a) Position the brake line into the two-part tool at the correct height using the gauge end of the tool.
  • 95. Figure 96-16 (b) Making an ISO flare requires a special tool. (b) Assemble the two blocks of the tool together and clamp in a vise. Turn the tool around and thread it into the tool block. The end of the threaded part of the tool forms the “bubble” or ISO flare.
  • 96. Figure 96-17 Whenever disconnecting or tightening a brake line, always use the correct size flare-nut wrench. A flare-nut wrench is also called a tube-nut wrench or a line wrench.
  • 97. Brake Lines
    • Coiled Brake Line
      • Steel brake line is often coiled to allow movement between the brake components without stress that could lead to metal fatigue and breakage
  • 98. Figure 96-18 The coils in the brake line help prevent cracks caused by vibration.
  • 99. Brake Lines
    • Armored Brake Line
      • In many areas, the steel brake line is covered with a wire coil wrap
      • This type of brake line is called armored brake line
  • 100. Brake Lines
    • Armored Brake Line
      • This armor is designed to prevent damage from stones and other debris that could dent or damage the brake line
  • 101. Figure 96-19 Armored brake line is usually used in the location where the line may be exposed to rock or road debris damage. Even armored brake line can leak and a visual inspection is an important part of any brake service.
  • 102. Brake Lines
    • Flexible Brake Hose
      • Used on each front wheel to allow for steering and suspension movement and at the rear to allow for rear suspension travel
  • 103. Brake Lines
    • Flexible Brake Hose
      • These hoses can crack, blister, or leak, and should be inspected at least every six months
  • 104. Brake Lines
    • Flexible Brake Hose
      • Made from synthetic yarn (poly vinyl alcohol, abbreviated PVA) braided into position from multi-end yarn spindles
  • 105. Brake Lines
    • Flexible Brake Hose
      • Braiding the yarn allows the strength to withstand braking system pressure over 1,000 PSI (6,900 kPa)
  • 106. Brake Lines
    • Flexible Brake Hose
      • A typical brake hose has an inner tube and a cushion liner between the braided layers
  • 107. Brake Lines
    • Flexible Brake Hose
      • All three layers use ethylenepropylene- diene-monomer (EPDM)-type thermosetting polymers to prevent the hose from absorbing moisture
  • 108. Brake Lines
    • Flexible Brake Hose
      • An outside jacket is made from rubber and protects the reinforcement fabric from moisture and abrasion
      • The outside covering is also ribbed to hide surface blemishes
  • 109. Brake Lines
    • Flexible Brake Hose
      • It is not unusual for flexible brake lines to become turned around and twisted during a brake pad change
  • 110. Brake Lines
    • Flexible Brake Hose
      • A constricted brake hose can cause the brakes to remain applied, causing excessive brake pad wear and unequal braking
  • 111. Brake Lines
    • Flexible Brake Hose
      • A constricted flexible brake line can also cause the vehicle to pull to one side
      • Always replace flexible brake hoses in pairs
  • 112. Brake Lines
    • CAUTION: Never allow a disc brake caliper to hang by the flexible brake hose. Damage to the line can result. Always use a wire to support the weight of the caliper.
  • 113. Figure 96-21 Flexible brake hoses are used between the frame or body of the vehicle and the wheel brakes. Because of suspension and/or steering movement, these flexible brake lines must be strong enough to handle high brake fluid pressures, yet remain flexible. Note that this flexible brake hose is further protected against road debris with a plastic conduit covering.
  • 114. Figure 96-22 (a) Typical flexible brake hose showing the multiple layers of rubber and fabric.
  • 115. Figure 96-22 (b) The inside diameter (ID) is printed on the hose (3 mm).
  • 116. Figure 96-23 Brake hose fabric being woven at the factory.
  • 117. Figure 96-24 Typical flexible brake hose faults. Many faults cannot be seen, yet can cause the brakes to remain applied after the brake pedal is released.
  • 118. Figure 96-25 Flexible brake hose should be carefully inspected for cuts or other damage, especially near sections where the brake hose is attached to the vehicle. Notice the crack and cut hose next to the mounting bracket.
  • 119. FREQUENTLY ASKED QUESTION
    • What Is Blue Brake Fluid?
      • Some brake fluid vendors market a high-performance DOT 4 brake fluid that is dyed blue and is called super blue while others market a super DOT 4 that is yellow. These brake fluids are designed to be sold in Europe.
    ? BACK TO PRESENTATION
    • The advertising states that the bright color of the brake fluid makes it easy to see when all of the old fluid has been purged from the system during a brake fluid replacement procedure.
  • 120. FREQUENTLY ASKED QUESTION
    • What Is Hydraulic Brake System Mineral Oil?
      • Some French-built Citroen and British-designed Rolls- Royce vehicles use hydraulic system mineral oil (HSMO) as part of their hydraulic control systems. The systems in these vehicles use a hydraulic pump to pressurize hydraulic oil for use in the suspension leveling and braking systems.
    ? BACK TO PRESENTATION
    • CAUTION: Mineral hydraulic oil should never be used in a braking system that requires DOT 3 or DOT 4 polyglycol-based brake fluid. If any mineral oil, such as engine oil, transmission oil, or automatic transmission fluid (ATF), gets into a braking system that requires glycol brake fluid, every rubber part in the entire braking system must be replaced. Mineral oil causes the rubber compounds that are used in glycol brake fluid systems to swell.
    • To help prevent hydraulic system mineral oil from being mixed with glycol brake fluid, hydraulic mineral oils are green.
      • Figure 96-4 Both rubber sealing cups were exactly the same size. The cup on the left was exposed to mineral oil. Notice how the seal greatly expanded.
  • 121. REAL WORLD FIX
    • The Sinking Brake Pedal
      • This author has experienced what happens when brake fluid is not changed regularly. Just as many technicians will tell you, we do not always do what we know should be done to our own vehicles.
      • While driving a four-year-old vehicle on vacation in very hot weather in mountainous country, the brake pedal sank to the floor.
    • When the vehicle was cold, the brakes were fine. But after several brake applications, the pedal became soft and spongy and sank slowly to the floor if pressure was maintained on the brake pedal. Because the brakes were okay when cold, I knew it had to be boiling brake fluid. Old brake fluid (four years old) often has a boiling point under 300°F (150°C).
    • With the air temperature near 100°F (38°C), it does not take much more heat to start boiling the brake fluid. After bleeding over a quart (1 liter) of new brake fluid through the system, the brakes worked normally. I’ll never again forget to replace the brake fluid as recommended by the vehicle manufacturer.
    BACK TO PRESENTATION
  • 122. REAL WORLD FIX
    • The Pike’s Peak Brake Inspection
      • All vehicles must stop about halfway down Pike’s Peak Mountain in Colorado (14,110 ft [4,300 m]) for a “brake inspection.” When this author stopped at the inspection station, a uniformed inspector simply looked at the right front wheel and waved us on. I pulled over and asked the inspector what he was checking.
    • He said that when linings and drums/rotors get hot, the vehicle loses brake effectiveness. But if the brake fluid boils, the vehicle loses its brakes entirely. The inspector was listening for boiling brake fluid at the front wheel and feeling for heat about 1 ft (30 cm) from the wheel. The inspector used an infrared pyrometer to measure the front wheel brakes and if the brakes were too hot to continue, you would be instructed to pull over and wait for the brakes to cool.
    • The inspector recommended placing the transmission into a lower gear, which uses the engine to slow the vehicle during the descent without having to rely entirely on the brakes.
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  • 123. TECH TIP
    • Bend It Right the First Time
      • Replacing rusted or damaged brake line can be a difficult job. It is important that the replacement brake line be located in the same location as the original to prevent possible damage from road debris or heat from the exhaust. Often this means bending the brake line with many angles and turns.
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    • To make the job a lot easier, use a stiff length of wire and bend the wire into the exact shape necessary. Then use the wire as a pattern to bend the brake line. Always use a tubing bender to avoid kinking the brake line. A kink not only restricts the flow of brake fluid, but also weakens the line. To bend brake line without a tubing bender tool, use an old V-belt pulley.
    • Clamp the pulley in a vise, lay the tubing in the groove, and smoothly bend the tubing. Different diameter pulleys will create various radius bends.
    • NOTE: Always use a tubing cutter instead of a hacksaw when cutting brake line. A hacksaw will leave a rough and uneven end that will not flare properly except when forming an ISO flare. A hacksaw is used to provide a rough surface to allow the flaring tool to grip the line during the procedure. Always check the instructions that came with the flaring tool for the exact procedure to follow.
      • Figure 96-20 A tube bender being used to bend a brake line.