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Manual Transmissions
Purpose To change the torque going to the drive wheels
Needed to start vehicle from a stand still
Basic Theory Manually shifted Clutch disc rotates the input shaft Output shaft powers wheels
Transaxle A differential and transmission in the same housing Common in four wheel drive vehicles Manual or automatic transmissions
Parts Input shaft GearsSynchronizers Shift fork
PartsGear shift leverOutput shaft Transmission case
Input Shaft Driven by clutchTurns gears inside transmission
Transmission gears Provides a means of changing output torque and speed
Synchronizers Devices that help gears mesh into desired arrangement
Shift fork Unit for moving gears in and out of arrangement
Gear shift leverA lever that provides the driver with the ability to change the gear arrangement
Output Shaft Shaft that transfers power from the transmission to the wheelsTransfers power to drive shaft in a rear wheel drive vehicle
Transmission CaseHousing that encases transmission shafts, gears, and lubricant
Gear RatioDefinition: the number of rotations a drive gear has to turn before the driven gear turns once
Determining Gear Ratio
Found by dividing the number of teeth on the driven gear by the number of teeth on the drive wheel
Gear Reduction A smaller gear drives a larger gear Increases torque and decreases the speed
Over Drive Gear A large gear drives a smaller gear Torque is decreased and speed is increased
Gear types There are two types of gears found in manual transmissions Spur gears Helical gears
Spur Gears Teeth cut parallel to center shaft Not used for drive gears Used for gears that have to slide in and mesh with other gears Noisy
Helical Gears Teeth cut out of parallel to drive shaft Used for constant drive components More efficient Quiet
Gear back lash Small clearance between meshing gears Allows lubricant to flow between high friction gears Allows gears to expand during operation
Lubricant Splash lubricant Gears fling lubricant around transmission Gear oil: 80W to 90W (always check owners manual)
Transmission shafts Input shaft Counter shaft Reverse idler shaft Output shaft
Input shaft (AKA clutch shaft)Transfers power from clutch to the counter shaft Splined on clutch side and a fixed gear on the transmission side Whenever clutch is turning the input shaft is turning
Counter shaft (AKA cluster gear shaft)Holds counter shaft gears into mesh with the input shaft gear
Counter shaft does not turn
Reverse idler shaft Small shaft that supports idler gear Reverse idler gear meshes with gears on both the input shaft and the counter shaft
Output shaft (AKA Main shaft)Holds output gears and synchronizers Extends out of the transmission to power the drive wheels
Shift forks Sits around synchronizer sleeves
Transfers movement from the gear shifter linkage to the synchronizers
Problems Grinding sounds when shifting Worn gear change linkage Clutch grabbing Synchronizer gears grinding going into mesh
Problems Transmission noise Roaring, rumbling, whirling sounds Low lubricant, metal contaminants
Problems Difficulty shifting Problem with the linkage for the shifter mechanismClutch problems
Problems Jump out of gear Worn clutch pilot bearing causes vibration and wobbling of the transmission input shaft. The vibration and wobbling shakes the synchronizers out of gear
Problems Locked in gear Shifter assembly problems Broken drive gear teeth, bits stuck in gears