172 Manual Drive Trains and Axles Copyright by Goodheart-Willcox Co., Inc. forward. Other devices on some newer transmissions keep certain transmission gears from being selected when engine temperature is below normal. Manual Transmission Gear Oil Manual transmission gears are lubricated by gear oil contained in the transmission case. The rotating trans- mission gears throw oil onto the gear teeth and onto other stressed parts. This is called splash lubrication. Manual transmissions are usually filled at the factory with 80- or 90-weight gear oil. In rare instances, heavy 140-weight oil is used. Occasionally, the manufacturer fills some manual transmissions with automatic transmission fluid however, gear oil is recommended for topping off or refills. Manual Transmission Power Flow Manual transmission power flow can be understood by studying Figure 8-29 through Figure 8-35. These figures show the gear train of a typical five speed manual transmission. Power flow, which is the path that power takes through the drive train, is depicted by arrows pass- ing through the gears that are actually transmitting power. Study Figure 8-29 to note the relative position of the various parts of the transmission. Neutral In Neutral, the main drive gear turns the countershaft gear, Figure 8-29. All gears that are in constant mesh with the countershaft gear also turn. This includes first and sec- ond gears. On the fully synchronized transmission, it also includes the reverse and the reverse idler gears. However, since all synchronizer outer sleeves are in the Neutral posi- tion (centered on inner hub) and the reverse idler is in the disconnected position, no power reaches the output shaft, and it remains stationary. The vehicle does not move. Reverse Gear In reverse gear, power flows from the main drive gear into the countershaft gear, Figure 8-30. The reverse idler gear has been moved rearward and power from the counter shaft gear flows into the reverse idler gear. The reverse idler gear directs power into the large gear on the outside of the rear or first-and-second gear synchronizer. Since the outer sleeve of the first-and-second gear synchronizer has been moved to the center position, power does not flow through either the first or second gears. The output shaft and synchronizer gear, however, remain locked together. Rotation is reversed between the main drive gear and the countershaft gear. It is reversed again between the countershaft gear and the reverse idler gear. The rotation is reversed one last time between the reverse idler gear and the first-and-second gear synchronizer/ output shaft. Since the rotation has been reversed three times (an odd number) between input and output shafts, direction of the output shaft is opposite that of engine rotation. Note that Figure 8-30 shows the reverse idler gear below the countershaft. In the transmission, the idler gear is in mesh with the countershaft and first-and-second gear synchronizer teeth. First Gear In first gear, the input shaft’s main drive gear turns the countershaft gear, reversing direction, Figure 8-31. The countershaft gear turns the low gear on the output shaft, Reverse Input shaft Reverse idler moves into engagement with counter gear and 1st and 2nd synchronizer gears Output shaft Figure 8-30. In reverse, the reverse idler gear moves toward the rear of the transmission and into engagement with the coun- ter gear and the gear on the outer rim of the 1-2 synchronizer assembly. The reverse idler gear is drawn below the counter gear but is actually positioned between the counter gear and 1-2 synchronizer assembly. Power flows through the input gear, countershaft gear, reverse idler gear, 1-2 synchronizer assem- bly, and through the output shaft. This places the transmission in reverse gear. (Borg-Warner) Figure 8-29. Note the major parts of the 5-speed transmission in this illustration. The transmission is similar to 3- and 4-speed transmissions, with input and output shafts, a countershaft with various gears, and a reverse idler gear. Note that fifth is an overdrive gear. All of the gears on the output shaft, except the fifth gear, can rotate on the shaft. The 1-2 and 3-4 synchronizer assemblies are splined to the output shaft. (Borg-Warner) Neutral 3rd and 4th synchronizer 1st and 2nd synchronizer 5th synchronizer Reverse idler