chap94 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 94, the reader should be able to: • • • Prepare for ASE Manual Drive Train and Axles (A3) certification test content area “A” (Clutch Diagnosis and Repair) List the parts that are included in the clutch system Describe how the clutch works 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 94, the reader should be able to: • • • Explain the importance of proper clutch pedal freeplay List the steps necessary to replace a clutch Describe the characteristic noise each clutch component part makes when defective 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: Bushing candlestick • clutch disc • coil spring clutch • cushioning spring front bearing retainer lever style (pressure plate) marcel spring pilot bearing • pressure 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 KEY TERMS: quill • quill shaft release bearing slave cylinder torsional dampers • throwout bearing 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 PURPOSE AND FUNCTION OF A CLUTCH The clutch assembly is located between the engine and the  transmission/transaxle. The purpose and function of a clutch include  the following: To disconnect the engine from the transmission/transaxle to  permit the engine to remain running when the vehicle is stopped  and to permit the transmission/transaxle to be shifted Connect and transmit engine torque to the transmission/  transaxle To dampen and absorb engine impulses and drivetrain vibration To provide a smooth engagement and disengagement between  the engine and the transmission/transaxle 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 NOTE: The term transmission refers to rear­wheel­drive vehicles and the  term transaxle usually refers to front­wheel­drive vehicles that have a differential built into the unit. A separate differential is used with a  transmission 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 COMPONENT PARTS AND OPERATION OF A CLUTCH ASSEMBLY A clutch assembly consists of a clutch disc that is splined to the input  shaft of the transmission/transaxle. When the driver depresses the  clutch pedal, a throwout bearing (release bearing) is forced against  the fingers of the pressure plate, which is bolted to and rotates with  the flywheel.  When force is exerted on the center of the pressure plate, the pressure  is released from the clutch disc that has been forced against the engine  flywheel. With the pressure removed from the clutch disc, the engine  can be operated without transferring torque to the transmission/  transaxle See Figure 94–1 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 94–1 Typical automotive clutch assembly showing all related parts (Courtesy of LUK) 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 When the driver reduces force on the clutch pedal, the pedal return spring and the pressure plate spring  combine to return the clutch pedal to its at­rest position (clutch­engaged position) When the clutch pedal moves up, the pressure on the throwout bearing is released and the force against the  pressure plate spring(s) is released allowing the force of the pressure plate to clamp the clutch tightly  between the flywheel and the pressure plate See Figure 94–2 To summarize: When the clutch pedal is up, the clutch is engaged When the clutch pedal is down, the clutch is disengaged 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 CLUTCH PEDAL ADJUSTMENT As the clutch disc wears, the pressure plate moves closer to the  flywheel. This causes the clutch to engage when the clutch pedal is  higher and higher. Eventually, the clutch will start to slip if the  linkage is not adjusted to compensate for the normal wear Most hydraulic clutch linkage is self­adjusting and does not  require any adjustment in normal service. Some cable­operated  clutches are either self­adjusting or are adjusted easily. Some  cable­operated clutch linkage is adjusted either at the bulkhead  (firewall) where the cable exits the passenger compartment or at  the clutch fork Follow the adjustment procedures specified for the exact vehicle  being serviced 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 Most adjustment procedures specify a clutch pedal freeplay of 0.5 to 1.0 inch. Freeplay is the distance the clutch pedal can be  depressed without encountering any noticeable resistance This slight amount of freeplay assures that the clutch is fully  engaged and not partially engaged as could occur if there is no  freeplay in the pedal linkage 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 Check for Bulkhead Flex Many cable-operated clutch linkage problems are caused by flexing of the bulkhead (firewall) as the clutch pedal is depressed This movement of the bulkhead can cause the clutch to slip To prevent unnecessary clutch repairs, have an assistant observe the bulkhead near the clutch cable while the clutch pedal is depressed If there is movement of the sheet metal bulkhead, add reinforcing steel plate to the area 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 BLEEDING THE HYDRAULIC CLUTCH If the hydraulic system has been opened, air has to be bled from  the system. Fill the master cylinder with DOT 3 brake fluid and  open the bleeder valve at the slave cylinder. Gravity should force  the brake fluid to flow downward, expelling any trapped air that  may be in the system When brake fluid starts to drip from the bleeder valve, close the  bleeder valve and check the clutch for normal operation Sometimes. pressing the clutch pedal slowly as an assistant opens  the bleeder valve at the slave cylinder will force trapped air out This is manual bleeding and should be repeated until normal  clutch operation returns. See Figures 94–31 and 94–32.  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 94–31 The clutch slave cylinder is often corroded because of moisture absorbed by the brake fluid used in the hydraulic clutch This slave cylinder was disassembled to see if it could be overhauled rather than replaced 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 94–32 (a) The replacement hydraulic clutch for a Saturn includes the master cylinder (shown) with the line and the slave cylinder as an assembly The assembly is even filled with brake fluid! Do not open the master cylinder cap on this unit because Saturn did not provide any method of bleeding air out of the ignition 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 94–32 (b) The slave cylinder attaches to the bell housing of the transaxle 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 CLUTCH SYMPTOM GUIDE Clutch Slips Drive the vehicle to a safe location where it can be  accelerated safely Rapidly accelerate the vehicle in first or second gear  and rapidly shift the transmission into a higher gear Clutch Grabs  Clutch disc has oil on the surface Clutch linkage is binding Clutch Noises  Pilot bearing is defective or worn Release bearing is defective or worn 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 Clutch Replacement 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 Clutch Replacement (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 Clutch Replacement 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 The clutch not only transmits engine torque from the flywheel to  the transmission/transaxle it also absorbs engine­firing impulses  to reduce the vibration felt by the driver through the shift  linkage The clutch has to be depressed (clutch disengaged) to keep the  engine running with the transmission in gear and to shift from  one gear to another The clutch disc has friction material on both sides and is  clamped between the engine flywheel and the pressure plate The pressure plate bolts to and revolves with the flywheel A throwout (release) bearing is used to disengage the clutch by  depressing a lever or spring, which removes the clamping force  from the clutch disc 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.) The pilot bearing is supported by the front bearing retainer of  the transmission The linkage between the clutch pedal and the clutch fork can  be levers and rods, a cable, or a hydraulic connection The flywheel attaches to the engine and not only provides the  friction surface for one side of the clutch disc but also  dampens engine­firing impulses A dual­mass flywheel is used on many import, luxury, and  diesel vehicles to help dampen engine and driveline  vibrations 10 The clutch linkage can be adjusted on some vehicles to  provide about 1/2 inch to 1 inch of clutch pedal freeplay 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.) 11 It is a normal service procedure to replace the clutch disc,  pressure plate, and throwout bearing as well as the pilot bearing  every time the clutch is replaced. The flywheel should also be  removed from the engine and resurfaced or replaced 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 ... thicker portion facing the pressure plate Figure 94–10 Cutaway of the center section of a clutch plate showing the various layers of steel plates used in the construction Automotive Technology: Principles,... engagement as much as a softer lining Instead? ?of? ?a full circle? ?of? ?softer friction material, the disc may have  only a few segments or buttons? ?of? ?this ceramic­metallic material.  Clutches that use these discs, which are sometimes called “button ... side touches the friction surface? ?of? ?the pressure plate Friction material is either woven or molded from a mixture? ?of? ?other  materials. Woven materials are softer and help cushion clutch  engagement, but they may not last as long as moldedmaterials