1. Modern Automotive Technology PowerPoint for by Russell Krick
Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

2. Chapter 55
Manual Transmission
Fundamentals

3. Contents Basic transmission parts Purpose of a manual transmission
Gear fundamentals
Manual transmission construction
Transmission types
Transmission power flow
Other transmission designs
Speedometer drive
Manual transmission switches

4. Basic Transmission Parts Input shaft Gears Synchronizers Shift forks
Shift linkage
Gear shift lever
Output shaft
Transmission case

5. Basic Transmission Parts

6. Purpose of a Manual Transmission
A manual transmission is designed to change the vehicle’s drive wheel speed and torque in relation to engine speed and torque

7. Transmission Features
A manual transmission should:
be able to increase torque to the drive wheels for quick acceleration
supply different gear ratios to match load conditions
provide a reverse gear
provide an easy means of shifting gears
operate quietly with minimal power loss

8. Gear Fundamentals
Gears are discs with teeth machined on their perimeters (rims)
They transmit turning effort from one shaft to another
When gears are different sizes, output speed and torque change

9. Gear Drive
A small gear driving a larger gear increases torque and decreases speed

10. Gear Drive
A large gear driving a smaller gear decreases torque and increases speed

11. Gear Ratio
The number of revolutions a drive gear must turn before the driven gear completes one revolution
Calculated by dividing the number of teeth on the driven gear by the number of teeth on the drive gear
Gear Ratio = # of driven gear teeth
# of drive gear teeth

12. Gear Ratio
If the drive gear has 12 teeth and the driven gear has 24 teeth, the gear ratio is two-to-one
Gear Ratio = # of driven gear teeth
# of drive gear teeth
= 24 12
= 2, written 2:1

13. Gear Ratio

14. Transmission Gear Ratios
First gear approximately 3:1
Second gear approximately 2:1
Third (high) gear approximately 1:1
Reverse gear approximately 3:1

15. Gear Reduction Occurs when a small gear drives a larger gear
Increases turning force (torque)
Used in lower transmission gears

16. Overdrive Ratio Results when a larger gear drives a smaller gear
Output gear speed increases
Output torque is reduced

17. Gear Types
Two gear types are commonly used in automotive transmissions
spur gears
helical gears

18. Spur Gears Somewhat noisy
The teeth are cut parallel to the centerline of the gear shaft
Used for sliding gears such as reverse gear

19. Helical Gears The teeth are machined at an angle to the centerline
Quieter and stronger than spur gears
Used for main drive gears that are in constant mesh

20. Gear Types

21. Gear Backlash Distance between the meshing gear teeth
Allows lubricating oil to enter the high-friction area between the gear teeth
Allows the gears to expand during operation

22. Manual Transmission Lubrication
Bearings, shafts, and gears are lubricated by oil splash lubrication
As the gears rotate, they sling oil around inside the transmission
Typically, 80W or 90W gear oil is used

23. Transmission Bearings
Bearings reduce the friction between the surfaces of rotating parts
Three basic types are used:
ball bearings
roller bearings
needle bearings
Used between shafts and housing, or between gears and shafts

24. Transmission Bearings
Three types of antifriction bearings are used

25. Manual Transmission
Construction

26. Transmission Case Supports the bearings and shafts
Provides an enclosure for gear oil
Made of cast iron or aluminum
A drain plug and fill plug are provided
typically, the oil level should be level with the bottom of the fill plug hole at operating temperature

27. Extension Housing Bolts to the rear of the transmission case
Encloses the output shaft
Holds the rear oil seal

28. Front Bearing Hub Covers the front transmission bearing
Acts as a sleeve for the release bearing

29. Manual Transmission

30. Transmission Shafts At least four shafts are commonly used:
input shaft (clutch shaft)
countershaft (cluster gear shaft)
reverse idler shaft
output shaft (main shaft)

31. Input Shaft
Transfers rotation from the clutch disc to the countershaft gears
Any time the clutch disc turns, the input shaft gear turns

32. Countershaft
Holds the countershaft gears into mesh with the input gear and other gears
Located slightly below and to one side of the input shaft
Normally, it is locked in the case and does not turn

33. Reverse Idler Shaft Supports the reverse idler gear
Allows the reverse idler gear to mesh with gears on both the countershaft and output shaft

34. Output Shaft Holds the output gears and synchronizers
Connects to the drive shaft to turn the wheels
Gears are free to revolve on the shaft, but the synchronizers are locked on the shaft by splines

35. Transmission Shafts

36. Transmission Gears
The input shaft gear turns the countershaft gears, which then turn the output shaft gears

37. Output shaft rotation is reversed
Gear Ranges
Gear reduction
Direct drive
Output shaft rotation is reversed

38. A machined part of the steel input shaft
Input Gear
A machined part of the steel input shaft

39. Several gears machined from a single piece of steel
Countershaft Gear
Several gears machined from a single piece of steel

40. Reverse Idler Gear Assembly

41. Output Shaft Gears

42. Synchronizers Synchronizers have two functions:
prevent the gears from clashing (grinding) during engagement
lock the output gear to the output shaft

43. Synchronizer Theory
When the synchronizer is away from an output gear, the gear freewheels (spins freely) on the output shaft
When the synchronizer slides against the output gear, it locks the output gear to the output shaft
Power flows through the output shaft to the drive wheels

44. Synchronizer Construction
The hub is splined to the output shaft

45. Synchronizer Operation
When the driver shifts gears, the synchronizer sleeve slides on its splined hub toward the output gear
The blocking ring cone rubs on the side of the drive gear cone, causing friction between the two
The output gear, synchronizer, and output shaft begin to spin at the same speed

46. Synchronizer Operation

47. Synchronizer Operation
As soon as the speed is equalized, the sleeve can slide over the blocking ring and spur gear teeth on the output gear
This locks the output gear to the synchronizer hub and to the shaft
Power flows through that gear to the drive wheels

48. Synchronizer Operation

49. Fully Synchronized Transmission
All the forward output gears use a synchronizer
Allows the driver to downshift into any lower gear (except reverse) while the vehicle is moving

50. Transfer movement from the gear shift linkage to the sleeves
Shift Forks
Transfer movement from the gear shift linkage to the sleeves

51. Movement of the shift linkage moves the shift fork
Shift Fork Assembly
Movement of the shift linkage moves the shift fork

52. External Shift Rod Linkage

53. Internal Shift Rail Linkage

54. Internal Shift Rail Linkage

55. Column Shift Mechanism

56. Transmission Types There are several types:
three-speed
four-speed
five-speed
Some transmissions have an overdrive in high gear
Extra gear ratios are needed for the small, low-horsepower engines

57. Transmission
Power Flow

58. First Gear
Linkage rods move the shift forks so that the first gear synchronizer is engaged to the first output gear
The input shaft gear turns the countershaft gears
First gear is locked to the output shaft
A small gear on countershaft drives a larger gear on the output shaft
The gear ratio is about 3:1

59. First Gear

60. Second Gear
The first gear synchronizer is slid away from the first gear
The second-third synchronizer is then engaged
Power flow is through the second gear on the output shaft
The gear ratio is about 2:1

61. Second Gear

62. Third Gear
The synchronizer is slid over the small teeth on the input shaft gear
The synchronizer locks the input shaft directly to the output shaft
All the output shaft gears freewheel on the shaft
Power flow is straight through the transmission
The gear ratio is 1:1

63. Third Gear

64. Reverse
The synchronizer is moved into the reverse gear on the output shaft, locking the gear to the output shaft
Power flows through the countershaft, reverse idler gear, reverse gear, and to the output shaft

65. Reverse

66. Neutral
All the synchronizer sleeves are located in the center of their hubs
All the output shaft gears freewheel on the output shaft
No power is transmitted to the output shaft

67. Neutral

68. Overdrive In many transmissions, high gear is an overdrive
An overdrive gear ratio is less than 1:1
e.g. 0.87:1
Overdrive increases fuel economy

69. Five-Speed, Overdrive Transmission – Neutral

70. Five-Speed, Overdrive Transmission – 1st Gear

71. Five-Speed, Overdrive Transmission – 2nd Gear

72. Five-Speed, Overdrive Transmission – 3rd Gear

73. Five-Speed, Overdrive Transmission – 4th Gear

74. Five-Speed, Overdrive Transmission – 5th Gear

75. Five-Speed, Overdrive Transmission – Reverse

76. Other Transmission Designs
Many transmission design variations are used by the numerous auto manufacturers
Whether rear-wheel drive, front-wheel drive, or all-wheel drive, all transmissions use similar principles

77. Five-Speed Manual Transmission

78. Front-Engine, All- Wheel Drive Vehicle

79. Speedometer Drive
A worm gear on the output shaft drives the speedometer gear and cable
The gear on the output shaft turns a plastic gear on the end of the speedometer cable
The cable runs through a housing up to the speedometer head

80. Manual Transmission
Switches

81. Back-up Light Switch
Closed by the action of the reverse gear shift linkage
When shifted into reverse, the linkage closes the switch
The switch carries current to the back-up lamps

82. Ignition Spark Switch Used on a few vehicles
Allows distributor advance only when transmission in high gear
Reduces pollution by retarding ignition timing in low gears
Usually located on side of transmission