Manual Transmission Fundamentals

1
Manual Transmission Fundamentals

• Chapter 71

2
Objectives

• Describe the relationship between gears and
  torque
• Understand the basic types of gears
• Calculate gear ratios
• Trace the power flow through three-, four-, and
  five-speed transmissions
• Name all of the transmission parts

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Introduction

• Manual transmission
• Used with clutch
• Shifted between gears manually
• Transmission
• Used in rear-wheel-drive cars
• Transaxle
• Used in front-wheel-drive cars

4
Purpose of a Transmission

• Provide a means of changing torque to fit engine
  operating requirements
• Low gear
• Crankshaft turns three times to one turn of
  transmission output shaft
• Small gear drives a larger gear
• Gears provide leverage

5
Using Gears to Increase Torqueand Gear Ratio

• Driving gear smaller than driven gear
• Output speed decreases
• Output torque increases
• Gear radius
• Distance from center of a gear to its outside
  edge
• Gear ratio
• Number of teeth on driven gear divided by number
  of teeth on driving gear

6
Transmission Gear Ranges and Overdrive

• Transmissions in cars and light trucks
• Three-six forward gear ranges
• Overdrive
• Opposite of gear reduction
• Output shaft turns faster than input shaft
• Ratio a step beyond 11 ratio of high gear
• Planetary gears
• Automatic transmission with lock-up torque
  converter

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Final Drive Ratio and Gear Types and Operation

• Final drive ratio
• Ratio between transmission output shaft and
  differential ring gear
• Gear tooth shape
• Allows teeth to roll into and out of mesh with
  minimum friction
• Contact pattern where teeth of two gears meet
• Pitch diameter diameter of meshed gear
• Manual transmission uses two types of gear
• Spur and helical gear

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Spur Gears

• Simple gears with straight-cut teeth
• One tooth carrying the load at time
• No end thrust
• Transmission will not attempt to pop out of gear
• Backlash
• Clearance between meshing gear teeth
• Clicking sound results as one gear rolls out of
  contact and new one rolls in
• As backlash noise gains speed, it turns into gear
  whine

9
Helical Gears and Idler Gears

• Helical gears replaced spur gears
• Quieter
• Continuous flow of power across gear teeth
• Minimum backlash
• Greater gear strength
• More area of tooth contact
• Cause end thrust under load
• Idler gears
• Used between two other gears
• Changes output rotation direction

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Transmission Parts

• Power flows from clutch disc to input shaft
• Each forward gear has a synchronizer
• Keeps two meshing gears from clashing
• Shift linkage acts on shift forks within
  transmission to select gear range
• Power flows from input shaft to countergear
• Then to mainshaft or output shaft
• Parts are housed in transmission case
• Has drain and fill plugs for adding and draining
  oil

11
Transmission Lubricationand Transmission Bearings

• Transmission parts
• Separated by oil at all times
• Splash lubrication
• Oil moved throughout case by rotating gears
• Bearings support ends of almost all rotating
  parts
• Allow parts to rotate with very little friction
• Reverse idler shafts and gears
• Supported by bushings

12
Transmission Gears and Shafts

• Countergear
• Single part made of a series of gears that mesh
  with various gears on mainshaft
• Mainshaft
• Includes all transmission gears and synchronizers
  
• Manual transmission
• Forward gears in constant mesh
• Reverse idler gear is only gear that moves into
  mesh with another gear

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Synchronizer Assembly

• Helps two gears spinning at different speeds mesh
  without clashing
• Blocking ring synchronizers
• Shift collar fits around hub outside
• Gears are in constant mesh
• Rotate freely on bearing areas
• Splines on outside of hub become meshed with gear
  teeth
• Synchro assembly
• Locks input shaft gear to output shaft gear

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15
Gear Shift Mechanisms and Shift Patterns

• Major components
• Shift forks fit into grooves cut in outside of
  synchro collar
• Shift linkage internal shift rail or external
  rod
• Detent mechanism holds transmission in gear
• Spring tension holds detent balls into detent
  notches in shift rail
• Interlock mechanism prevents selection of two
  gears at once
• Shift patterns various patterns for different
  transmissions

16
Transmission Power Flow

• Modern transmissions are constant mesh
• Synchro collar only thing that moves
• All manual transmissions operate in a similar
  fashion
• Whether there are three speeds or six speeds
• Five-speed transmissions most common today
• Most have direct power in fourth gear
• Fifth gear provides an overdrive

17
Four-Speed Transmission Power Flow

• Four-speed transmission without overdrive
• Neutral synchro sleeves centered and do no mesh
  with clutch teeth of any gear
• High gear power runs straight through the
  transmission from input to output shaft
• Third gear power enters through input shaft
• Second gear rear synchro sleeve engages engage
  the second-gear clutch teeth
• First-gear rear synchro sleeve is moved toward
  rear to engage first-gear clutch teeth
• Reverse synchro sleeves are in neutral position

18
Five-Speed Transmission

• Gear flow in five-speed
• Same as in first four speeds
• Extra gears in extension housing
• Fifth gear synchro sleeves in transmission case
  in neutral position
• Power flow through end of countergear to gear at
  the end of countergear
• Some have both reverse and fifth gear in
  extension housing or rear section of case

19
Speedometer Drive

• Some cars use electric speedometers
• Receive signal from vehicle speed sensor (VSS)
• Vehicles with VSS
• If the tire diameter is changed computer can
  often be programmed with new tire information
• Speedometer will be accurate
• Speed inputs to the computer will be meaningful

20
Switches and Sensors

• Computer technology
• Provided several electronic features to
  transmissions
• VSS on late-model transmissions
• Shift blocking solenoids
• Reverse lockout
• Gear range selector switch
• Sensors are not prone to wear like a switch that
  has electrical contacts