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

3. Introduction Manual transmission Used with clutch Transmission
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 Torque and 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 1:1 ratio of high gear
Planetary gears
Automatic transmission with lock-up torque converter

7. Final Drive Ratio and Gear Types and Operation
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

8. Spur Gears Simple gears with straight-cut teeth Backlash
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

10. 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 Lubrication and 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

13. 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

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