chap84 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 84, the reader should be able to: • Prepare for ASE Suspension and Steering (A4) • • • • • certification test content area “E” (Wheel and Tire Diagnosis and Repair) Discuss proper tire mounting procedures Describe recommended tire rotation methods Discuss how to properly balance a tire Describe tire repair procedures Explain wheel and tire safety precautions 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: dynamic balance • lateral runout match mounting • modified X radial force variation • radial runout shimmy • static balance tire rotation • tramp wheel mounting torque 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 Proper tire service is extremely important for the safe operation of any vehicle Premature wear can often be avoided by checking and performing routine service, such as frequent rotation and monthly inflation checks 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 84–1 Using soapy water from a spray bottle is an easy method to find the location of an air leak from a tire 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 TIRE INFLATION Tires should be inflated to pressure indicated on the door or pillar sticker Tires should be checked when cold, before the vehicle has been driven; driving increases temperature and pressure of tires Proper tire inflation is important for several reasons: Inflation pressure carries the load of the vehicle If the pressure is low, the load capacity of the tire is decreased Figure 84–2 This chart shows the relationship between tire inflation pressure and load capacity of the tire 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 Inflation pressure varies with temperature Tires lose psi for every 10-degree drop in temperature This means as the sensors change and temperature changes, so does pressure inside the tires If tires were inflated to 35 psi on the first day of summer (June 21) when the temperature was 90°F (32°C), then the following pressures would occur, assuming no air loss at all: Summer (June 21) 90°F—35 psi Fall (September 21) 80°F—34 psi Winter (December 21) 30°F—29 psi It is very important to check and correct inflation pressures regularly 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 Tire inflation affects fuel economy A drop in inflation pressure from 30 psi to 23 psi can result in a drop of fuel economy from 20 miles per gallon to 18 miles per gallon Figure 84–3 This chart shows that a drop in inflation pressure has a major effect on fuel economy 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 Tire inflation affects tire life Even a slight drop in air pressure can have a major effect on the life of a tire If, for example, the inflation pressure dropped 10 psi, the life of the tire would be reduced by 40% Figure 84–4 Notice that if a tire is underinflated by 10 PSI, the life expectancy is reduced by 40% 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 TREAD Act specifies that the driver be notified if the inflation of a tire drops by 25% 25% represents a loss of air pressure of about psi A drop of psi means an approximate 2-mpg decrease in fuel economy as well as about a 25% reduction in tread wear Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 10 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 It Happened to Me—It Could Happen to You During routine service, I rotated tires on a Pontiac Trans Am Everything went well and I even used a torque wrench to properly torque all of the lug nuts Then, when I went to drive the car out of the service stall, I heard a horrible grinding sound When I hoisted the car to investigate, I discovered that the front wheels were hitting the outer tie rod ends The 16-in wheels had a different back spacing front and rear, and therefore these wheels could not be rotated Always check replacement or aftermarket wheels for proper fit before driving the vehicle Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 84–32 Notice that the rim touches the tie rod end 62 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 What are Hubcentric Wheels? Most wheels are designed to fit over and be supported by the axle hub Some wheels use an enlarged center hub section and rely on wheel studs for support and to keep the wheel centered on the axle Some aftermarket wheels may be designed to fit several different vehicles As a result, the wheel manufacturers use plastic hubcentric adapter rings (a) (b) Figure 84–33 (a) A hubcentric plastic ring partially removed from an aftermarket wheel (b) A hubcentric plastic ring left on the hub when removing a wheel Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 63 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 TIRE REPAIR Tread punctures, nail holes, or cuts up to 1/4 in (2.6 mm) can be repaired Repairs should be done from the inside of the tire using plugs or patches With the tire off the wheel, inspect the wheel and the tire for hidden damage The proper steps to follow for a tire repair are as follows: Mark the location of the tire on the wheel Dismount the tire; inspect and clean the punctured area with a prebuff cleaner DO NOT USE GASOLINE! Buff the cleaned area with sandpaper or a tire-buffing tool until the rubber surface has a smooth, velvet finish See Figure 84–34 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 64 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Ream the puncture with a fine reamer from the inside Cut and remove any loose wire material from the steel belts Figure 84–34 The area of the repair should be buffed slightly larger than the patch to be applied Fill the puncture with contour filling material, and cut or buff the material flush with the inner liner of the tire Apply chemical vulcanizing cement and allow to dry Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 65 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Apply the patch and use a stitching tool from center toward the outside of the patch to work any air out from between the patch and the tire Figure 84–35 A stitching tool being used to force any trapped air out from under the patch Figure 84–36 A rubber plug being pulled through a hole in the tire The stem is then cut off flush with the surface of the tire tread Another excellent tire repair procedure uses a rubber plug Pull the stem through the hole in the tire, as shown Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 66 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Remount the tire on the rim, aligning the marks made in step Inflate to the recommended pressure and check for air leaks There are many tire repair products on the market Always follow the installation and repair procedures exactly per the manufacturer’s instructions CAUTION: Most experts agree that tire repairs should be done from the inside Many technicians have been injured and a few killed when the tire they were repairing exploded as a steel reamer tool was inserted into the tire The reamer can easily create a spark as it is pushed through the steel wires of a steel-belted tire This spark can ignite a combustible mixture of gases inside the tire caused by using stop leak or inflator cans Since there is no way a technician can know if a tire has been inflated with a product that uses a combustible gas, always treat a tire as if it could explode Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 67 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Dispose of Old Tires Properly Old tires cannot be thrown out in the trash They must be disposed of properly Tires cannot be buried because they tend to come to the surface They also trap and hold water, which can be a breeding ground for mosquitoes Used tires should be sent to a local or regional recycling center where the tires will be ground up and used in asphalt paving or other industrial uses Because there is often a charge to dispose of old tires, it is best to warn the customer of the disposal fee NOTE: Most vulcanizing (rubber) cement is highly flammable Use out of the area of an open flame Do not smoke when making a tire repair Open-End Wrenches Make It Easier Tire repair is made easier if two open-end wrenches are used to hold the beads of the tire apart See step in the tire repair photo sequence Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 68 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Tire Mounting Step-By-Step Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 69 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Tire Mounting Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) 70 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Tire Mounting Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) 71 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Tire Repair Step-By-Step Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 72 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Tire Repair Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) 73 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY For safety and proper vehicle handling, all four tires of the vehicle should be of the same size, construction, and type, except where specified by the manufacturer, such as on some high-performance sports cars Wheels should always be tightened with a torque wrench to the proper torque in a star pattern Tires should be rotated every 5,000 to 7,000 miles (8,000 to 11,000 km), or at every other oil change Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 74 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Wheels should be cleaned around the rim area whenever tires are changed and carefully inspected for cracks or other defects such as excessive lateral or radial runout Properly balanced tires prolong tire life Wheel tramp or an up and-down type of vibration results if the tires are statically out of balance or if the tire is out-of-round Dynamic balance is necessary to prevent side-to-side vibration, commonly called shimmy Only coated or stick-on-type wheel weights should be used on alloy wheels to prevent corrosion damage Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 75 ©©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 76 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458