chap75 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 75, the reader should be able to: • • • Prepare for ASE Brakes (A5) certification test content area “B” (Drum Brake Diagnosis and Repair) Discuss the procedure recommended for brake drum removal Discuss the inspection and lubrication points of the backing plate 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 75, the reader should be able to: • • Explain the importance of the proper drum brake hardware Disassemble and reassemble a drum brake assembly 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: bearingized • brake hardware kits core speed nuts tinnerman nuts 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 DRUM DIAGNOSTIC PROCEDURE Diagnosing brake concern includes the following steps: Step #1 Verify the customer complaint (concern) For example, common drum brake concerns include: • • • • Low brake pedal Parking brake does not hold the vehicle on a hill Noise while braking Noise when the vehicle is moving, but brakes are not applied Step #2 Perform a visual inspection of the brakes and related parts, such as the wheels, tires, and suspension 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 Step #3 Determine the root cause For example, this could include determining that the parking brake is corroded causing the brake shoes to wear Replacing just the brake shoes will not correct the root cause Step #4 Restore the brake system to like-new operation, which is the purpose of any repair Step #5 Test drive the vehicle to verify that the service has corrected the customer’s complaint 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 Drum brake service usually involves the following steps: Step #1 Removing the brake drums Step #2 Inspect the brake drums for damage and measure the inside diameter and compare to specifications Step #3 Inspect brake linings and hardware for wear or damage Step #4 Inspect the wheel cylinder and brake lines for leakage Step #5 Check the backing plate for excessive rust or wear 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 DRUM REMOVAL The drum has to be removed before inspection or repair of a drum brake can begin There are two types of drums, and removal procedure depends on which type is being serviced With either type it is recommended that the drums be marked with an “L” for left or an “R” for right so that they can be replaced in the same location 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 CAUTION: Proper precaution should be taken to prevent any asbestos that may be present in the brake system from becoming airborne Removal of the brake drum should occur inside a sealed vacuum enclosure equipped with a HEPA filter or washed with water or solvent Figure 75–1 A liquid soaking solvent, such as brake cleaner, should be used to wet the linings The purpose of wetting the lining material while the drum is still on the vehicle is to prevent the possibility of asbestos from the lining becoming airborne Asbestos is only hazardous when asbestos dust is airborne and is breathed in during brake system service 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 Hub or Fixed Drums A fixed or hub-mounted drum is often used on the rear of front-wheel-drive vehicles The drum has a hub for inner and outer bearings and is retained by a spindle nut To remove the brake drum, remove the dust cap and cotter key that is used to retain the spindle nut Remove spindle nut and washer and the brake drum can be carefully pulled off the spindle CAUTION: Overheating or not allowing the drum to cool slowly can cause the brake drum to distort Using a puller can also damage a drum 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 The Masking Tape Trick Some technicians cover the friction material with masking tape to prevent contaminating the linings with dirt or grease during installation After everything has been installed and double-checked, the masking tape is removed and the brake drums are installed Figure 75–26 To prevent getting grease on the lining, the wise service technician covers the friction material with masking tape The tape is removed after the brake shoes have been 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 LUBRICATION CHECKLIST For proper operation, the following points should be lubricated with approved brake lubricant: The starwheel adjuster threads and under end caps The backing plate contact areas (pads or ledges) Anchor pins Also check and lubricate the parking brake cable, if necessary CAUTION: Do not use wheel bearing or chassis grease on a braking system Use brake lubricant such as molybdenum disulfide (moly) grease, synthetic grease, lithium-based brake grease, or antiseize compound 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 SYMPTOM-BASED TROUBLESHOOTING GUIDE Low Pedal or the Pedal Goes to the Floor Excessive clearance between the linings and drum Automatic adjusters not working Leaking wheel cylinder Air in the system Springy, Spongy Pedal Drums worn below specifications Air in the system Pulsating Brake Pedal (Parking Brake Apply Pulsates Also) Drums out-of-round 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 Excessive Pedal Pressure Required to Stop the Vehicle Grease or fluid-soaked linings Frozen wheel cylinder pistons Linings installed on wrong shoes Light Pedal Pressure—Brakes Too Sensitive Brake adjustment not correct Loose backing plate Lining loose on the shoe Excessive dust and dirt in the drums Scored, bell-mouthed, or barrel-shaped drum Improper lining contact pattern 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 Pedal Travel Decreasing Weak shoe retracting springs Wheel cylinder pistons sticking Snapping Noise in the Front End Grooved backing plate pads Loose backing plates Shoe Click Shoes lift off the backing plate and snap back Hold-down springs weak Shoe bent Grooves in the backing plate pads 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 Thumping Noise When Brakes Are Applied Cracked drum; hard spots in the drum Retractor springs unequal—weak Wet Weather: Brakes Grab or Will Not Hold Bent backing plate flange Incorrect or abused shoe and linings Grinding Noise Shoe hits the drum Bent shoe web Brake improperly assembled 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 One Wheel Drags Weak or broken shoe retracting springs Brake-shoe-to-drum clearance too tight—brake shoes not adjusted properly Brake assembled improperly Wheel cylinder piston cups swollen and distorted Pistons sticking in the wheel cylinder Drum out-of-round Loose anchor pin/plate Parking brake cable not free Parking brake not adjusted properly 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 Vehicle Pulls to One Side Brake adjustment not correct Loose backing plate Linings not of specified kind; primary and secondary shoes reversed or not replaced in pairs Water, mud, or other material in brakes Wheel cylinder sticking Weak or broken shoe retracting springs Drums out-of-round Wheel cylinder size different on opposite sides Scored drum 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 Brakes Squeak Backing plate is bent or shoes twisted Shoes scraping on backing plate pads Weak or broken hold-down springs Loose backing plate, anchor, or wheel cylinder Glazed linings Dry shoe pads and hold-down pin surfaces 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 Brakes Chatter Incorrect lining-to-drum clearance Loose backing plate Weak or broken retractor spring Drums out-of-round Tapered or barrel-shaped drums Improper lining contact pattern 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 PHOTO SEQUENCE Drum Brake Service Step-By-Step 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 PHOTO SEQUENCE Drum Brake Service (cont.) 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 PHOTO SEQUENCE Drum Brake Service Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY Care should be exercised when removing a brake drum so as not to damage the drum, backing plate, or other vehicle components After disassembly of the drum brake component, the backing plate should be inspected and cleaned Most experts recommend replacing the wheel cylinder as well as all brake springs as part of a thorough drum brake overhaul Measure the brake drum and adjust brake shoes to fit the drum Use care to prevent getting grease on brake linings It can cause the brake to grab 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