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A manual transmission (MT), also known as manual gearbox, standard transmission (in Canada, the United Kingdom, and the United States), or stick shift (in the United States), is a multispeed motor vehicle transmission system, where gear changes require the driver to manually select the gears by operating a gear stick and clutch (which is usually a foot pedal for cars or a hand lever for motorcycles). Early automobiles used sliding mesh manual transmissions with up to three forward gear ratios. Since the 1950s, constant mesh manual transmissions have become increasingly commonplace and the number of forward ratios has increased to 5 speed and 6 speed manual transmissions for current vehicles.
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 95, the reader should be able to: • • • Prepare for the ASE Manual Drive Train and Axles (A3) certification test content area “B” (Transmission Diagnosis and Repair) and content area “C” (Transaxle Diagnosis and Repair) Explain how to calculate gear ratios Name the parts of a typical manually shifted 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 OBJECTIVES: After studying Chapter 95, the reader should be able to: • • • Describe how the synchronizer assembly allows for smooth, clash-free shifting Describe the different types of lubricants that may be used in a manual transmission/transaxle Diagnose a difficult-to-shift manual transmission/transaxle 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: axis back taper • bell housing • bevel gear • blocker ring cluster gears • cluster shaft • cluster gear • constant-mesh gear • counter gears • countershaft direct drive • drive gear • driven gear extension housing • external gears fifth gear • final drive assembly • first gear • fourth gear • front bearing retainers 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: gear reduction helical gear • hypoid gear set input shaft • internal ring gears keys lay shaft main drive pinion assembly • main gear • main shaft neutral 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: output shaft • overdrive pinion gear quill reverse second gear • sliding reverse gear • sliding sleeve • springs • spur gear • stop ring • synchronizer assemblies • synchronizer ring third gear • transmission case 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 NEED FOR A TRANSMISSION A vehicle requires a lot of torque to start off and to climb hills, yet it does not require as much torque to move on level ground Torque is a twisting or turning force that is exerted on the input shaft of a transmission/transaxle An engine produces increasing torque as its speed increases up to a certain point where the torque output starts to decrease To get a vehicle moving or to accelerate up a hill, it is desirable to use a transmission that allows the engine speed to be increased even though the vehicle speed may be low Using gears allows the engine speed to increase at low vehicle speeds yet still permits it to drop at higher speeds to save fuel and reduce emissions 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 First gear: Vehicle speed is low, engine speed is high Second gear: Vehicle speed increases, engine speed decrease Third gear: Vehicle speed continues to increase, engine speed is kept in a narrow range Fourth gear: Again, the vehicle speed is increasing, yet engine speed is about the same as in third gear What Is the Difference Between a Transmission and a Transaxle? A transmission is used on rear-wheel-drive vehicles, whereas a transaxle is usually used on front-wheel-drive vehicles A vehicle equipped with a transmission uses a separate differential to split the torque equally to the drive wheels.A transaxle includes a differential assembly In a transaxle, the differential, sometimes called the final drive unit, is incorporated in the construction of the 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 GEAR TYPES The simplest type of gear is the spur gear, consisting of a gear blank with straight-cut teeth around its entire circumference All gear teeth lie parallel to the centerline, or axis, of the gear The teeth are shaped so they can mesh without slippage with a second spur gear’s teeth positioned along a parallel axis Figure 95–1 Spur gears have straight-cut teeth 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 helical gear, although similar to a spur gear, has its teeth cut at an angle to the axis of the gear This enables more teeth, 2.5 to 3.5, to mesh at a time than the spur gear The angle allows the teeth to mesh gradually, rather than all at once As a result, helical gears run quieter than spur gears Helical gears have two disadvantages Each gear pushes against its shaft parallel to its axis Special bearings are needed to protect the gearbox from this type of axial, or thrust, loading Because of the increased contact area, helical gears create more friction than spur gears See Figures 95–2 and 95–3 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