Post on 04-Jan-2016
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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
• 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