Chapter 8 Manual Transmission Construction and Operation 177 Copyright by Goodheart-Willcox Co., Inc. releases, and the third gear, which was already applied in fourth, delivers power through the transmission. The same sequence applies to all downshifts. Skipping Gears The driver can bypass, or skip, gears as desired. To shift from fifth to second for instance, the driver moves the shift lever to the second gear position. The control system will release the odd gear clutch and apply the even gear clutch while engaging the second gear. Although the control system works very quickly, the driver may feel a slight delay as the shift is made. Another type of dual transmission is shown in Figure 8-44. This six-speed design has two output shafts which join to the main output shaft through gears. This transmission illustration also shows simplified synchro- nizer assemblies used to select gears. The reason for having two output shafts is to have a more compact case design. Summary The vehicle driver selects manual transmission gears. Operation of a manual transmission is simple. The clutch pedal is depressed, and the proper gear is selected by using the gearshift lever. Then, the clutch pedal is released to allow power to flow to the rear wheels. There are seven major parts to a manual transmission. These are the transmission shafts and gears, the synchro- nizers, the shift forks and linkage, and the transmission case and extension housing. Transmission shafts are used to support gears and to transmit motion. A shaft may rotate, or it can be a stationary support for a moving gear. The major shafts in a manual transmission are the input shaft, countershaft, output shaft, and reverse idler shaft. Transmission gears may rotate on transmission shafts or may be solidly connected to them. Gears transmit power and provide different gear ratios and a way to reverse the vehicle. The engine turns the input shaft and main drive gear whenever the clutch is engaged. The main drive gear is always in mesh with the countershaft gear. This gear turns whenever the main drive gear turns. The output shaft con- tains gears that provide forward speeds. It also contains reverse gear. The reverse idler gear is in mesh with the coun- tershaft gear. Through the idler gear, rotational direction of the output shaft is made opposite of the input shaft. In this way, the vehicle can be reversed. Synchronizers are used to select various gears by matching gear speeds to avoid gear clash. They consist of a splined outer sleeve, an inner hub, and blocking rings, which match cone-shaped extensions on mating gears. When the synchronizer is pushed into engagement with the cone, it acts as a clutch, speeding up or slowing down one gear to match the speed of the output shaft. Most modern transmissions are synchronized in all forward gears. In some transmissions, however, low and reverse gears are selected by sliding the main drive gears directly into mesh with the countershaft gears. The vehicle driver operates the synchronizer outer sleeves through shift forks. Shift forks slip into grooves cut in the outer sleeves. The shift fork moves in a straight line to push the sleeve into engagement with a mating gear. The sleeve can continue to rotate as it is moved. The driver operates the shift forks through a series of shafts, levers, links, and sometimes cables. External shift linkage is a system that is identified as a series of rods and levers that connect to the outside of the transmission. External shift linkage may be connected to the gearshift lever either on the steering column or on the floor. Internal shift linkage is found only on transmissions with floor-mounted gearshift levers. Except for the gearshift lever, all linkage is internal to the transmission. This type of linkage may employ a single shifter shaft or several shift rails. The shift forks are positioned along the shaft. The transmission case houses, supports, and aligns the rotating transmission components. It forms a reservoir for lubricant. It is the attaching point for the clutch housing, extension housing, shift linkage, and other components. Many modern transmissions are made with a center support. The front bearing retainer is installed on the front of the transmission case, around the input shaft. It forms a support for the front bearing. The clutch throwout bearing slides on the nose of the front bearing retainer. The extension housing supports and protects the end of the transmission output shaft. The front of the extension housing is bolted to the transmission case. The extension housing also contains the speedometer pinion gear and adapter and worm gear. The transmission mount is usually attached to the extension housing. Most late-model transmissions will be equipped with one or more electrical switches, sensors, and solenoids. Switches and sensors are used to turn on the backup lights Figure 8-44. This six-speed transmission is similar to the five speed previously illustrated, but has two output shafts. The shafts connect through gears with a main output shaft at the right to deliver power to the driveshaft. Output shaft Even gear clutch Odd gear clutch Typical gear selector 2 4 5 6 R 3 1 Inner input shaft Outer input shaft Output gearset