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 Gears Synchronizers Shift fork

Parts Gear shift lever Output shaft Transmission case

Input Shaft Driven by clutch Turns 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 lever A lever that provides the driver with the ability to change the gear arrangement

Output Shaft Shaft that transfers power from the transmission to the wheels Transfers power to drive shaft in a rear wheel drive vehicle

Transmission Case Housing that encases transmission shafts, gears, and lubricant

Gear Ratio Definition: 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 owner’s 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 mechanism –Clutch 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