chap71 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 71, the reader should be able to: • • • • • Prepare for ASE Brakes (A5) 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 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 71, the reader 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 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: armored brake line brake fluid • brake lines • brake pipes • brake tubing DOT • DOT • DOT • DOT 5.1 • double flare elastomers • flexible brake hoses hydraulic system mineral oil (HSMO) • hygroscopic International Standards Organization (ISO) nonhygroscopic • polyglycol • silicone brake fluid Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 BRAKE FLUID Brake fluid is designed to function in the hydraulic brake system under all operating conditions Brake fluid boiling point is one of the most critical aspects and ratings for brake fluid As brake fluid ages, it absorbs moisture, which lowers its boiling point and causes increased corrosion of the brake system components Automotive experts agree that brake fluid should be changed regularly as part of normal routine service Getting the old lowboiling-point brake fluid out of the system could prevent a total loss of brakes due to brake fluid boiling! Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 All brake fluids must be able to pass tests for the following: Fluidity at low temperatures Controlled percentage loss to evaporation at high temperatures (212°F [100°C]) Compatibility with other brake fluids Resistance to oxidation Specific effects on rubber, including: a No disintegration b No increase in hardness of rubber tested c Limited amount of decrease in hardness of the rubber Figure 71–1 Brake fluid can absorb moisture from the air even through plastic, so many experts recommend that brake fluid be purchased in metal containers Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 BRAKE FLUID TYPES Brake fluid is made from a combination of various types of glycol, a non-petroleum-based fluid Brake fluid is a polyalkylene– glycol–ether mixture called polyglycol for short All polyglycol brake fluid is clear to amber in color Brake fluid has to have the following characteristics A high boiling point A low freezing point No ability to damage rubber parts in the brake system Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 BRAKE FLUID SPECIFICATIONS All automotive brake fluid must meet federal Motor Vehicle Safety Standard 116 The SAE and the Department of Transportation (DOT) have established brake fluid specification standards as shown in the following chart: See the chart on Page 849 of your textbook Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 DOT The type most often used is DOT Important characteristics: DOT can absorb 2% of its volume in water per year through microscopic seams in the brake system and around seals Over time, the water will corrode the system and thicken the brake fluid The moisture can also cause a spongy brake pedal, due to reduced vapor-lock temperature DOT must be used from a sealed (capped) container If allowed to remain open for any length of time, DOT will absorb moisture from the surrounding air, which is called hygroscopic Always check brake fluid recommendations on the top of the master cylinders of imported vehicles before adding DOT See Figure 71–2 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 71–2 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 CAUTION: DOT brake fluid is a very strong solvent and can remove paint! Care is required when working with DOT brake fluid to avoid contact with the vehicle’s painted surfaces It also takes the color out of leather shoes Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Always use two line wrenches when disconnecting or reattaching brake lines Figure 71–16 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 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 COILED BRAKE LINE Steel brake line is often coiled, as shown here Coils allow movement between brake components without stress that could fatigue metal and cause line breakage Figure 71–17 The coils in the brake line help prevent cracks caused by vibration The master cylinder attaches to the bulkhead of the vehicle; the combination valve often attaches to the frame Because body and frame are insulated from each other using rubber isolators, some movement occurs while driving Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ARMORED BRAKE LINE In many areas of the brake system, the steel brake line is covered with a wire coil wrap, as shown here This type of brake line is called armored brake line Figure 71–18 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 This armor is designed to prevent damage from stones and debris that dent or damage the brake line If a section of armored brake line is to be replaced, armored replacement line should be installed Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Bend It Right the First Time - Part Replacing rusted or damaged brake line can be a difficult job It is important 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 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 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 and a hacksaw is used to provide a rough surface to allow the flaring tool to grip the line during the procedure Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Bend It Right the First Time - Part 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 Figure 71–19 Using a V-belt pulley in a vise to bend brake line Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 FLEXIBLE BRAKE HOSE Flexible brake hoses are used on each front wheel to allow for steering and suspension movement and at the rear to allow for rear suspension travel Figure 71–20 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 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 These rubber high-strength hoses can crack, blister, or leak, and should be inspected at least every six months (a) Figure 71–21 (a) Typical flexible brake hose showing the multiple layers of rubber and fabric (b) The inside diameter (ID) is printed on the hose (3 mm) (b) CAUTION: Never allow a disc brake caliper to hang by the flexible brake line Damage to the line can result Always use a wire to support the weight of the caliper Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 71–22 Brake hose fabric being woven at the Delco Chassis plant in Dayton, Ohio, USA Flexible brake hose is made from synthetic yarn (poly vinyl alcohol, abbreviated PVA) that is braided into position from multiend yarn spindles By braiding the yarn, all of the strands operate in tension and, therefore, have great strength to withstand braking system pressure over 1000 psi (6,900 kPa) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 A typical brake hose has an inner tube for conveying the brake fluid and a cushion liner between braided layers to prevent the braids from chafing All three layers use ethylene- propolyenediene-monomer (EPDM)-type thermosetting polymers, to help prevent the hose from absorbing moisture from the outside air An outside jacket is made of rubber and protects reinforcement fabric from moisture and abrasion The outside covering is also ribbed as part of the manufacturing process to hide surface blemishes These ribs also make it easy for the tech to see if the hose is twisted It is not unusual for flexible brake lines to become turned around and twisted when the disc brake caliper is removed and then replaced during a brake pad change See Figures 71–23 & 71–24 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 71–23 All brake hose is carefully inspected and a 3-mm-diameter gauging tool is inserted through the hose to make sure the hose is not restricted Note the small diameter of the tool compared to the diameter of the hose Seeing how small the inside diameter of the hose actually is makes it easier to visualize how easy it would be to have a restricted or blocked flexible hose Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 71–24 Typical flexible brake hose faults Many faults cannot be seen, yet can cause the brakes to remain applied after the brake pedal is released Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 A constricted brake hose can cause brakes to remain applied, causing excessive brake pad wear and unequal braking A constricted brake line can also cause vehicle pull to one side Figure 71–25 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 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY Most brake fluid is amber in color and polyglycol based DOT is the type of brake fluid most often recommended for use Brake fluid absorbs moisture over time and can remove paint DOT and DOT 5.1 are also polyglycol-based fluids, whereas DOT is silicone based Brake fluid should be checked for proper level and color and tested for condition or for contamination Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Brake fluid should be disposed of according to local and state guidelines Most brake systems use EPR or SBR-type rubber that is compatible with brake fluid but they can swell in size if exposed to mineral oil such as power steering fluid, engine oil, or automatic transmission fluid Brake lines are double-walled steel with a rust prevention coating with either a double lap flare or an ISO flare end Flexible brake hose is constructed of braided synthetic yarn and EPDM rubber Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ... Petroleum or mineral oil fluids will float on the surface of the water, retain their color and also dissolve the Styrofoam cup at the waterline Automotive Technology: Principles, Diagnosis, and... vibration The master cylinder attaches to the bulkhead of the vehicle; the combination valve often attaches to the frame Because body and frame are insulated from each other using rubber isolators,... the use of or the mixing of other types of polyglycol brake fluid and specify the use of DOT brake fluid only Always follow the vehicle manufacturer’s recommendation Continued Automotive Technology: