1. Gears and Transmissions

2. Why Is a Transmission Necessary?
Provide torque multiplication at low speeds
Reduce engine RPM at highway speeds
Allow the engine to operate within its most efficient RPM range
Allows the engine to be disengaged from the rear wheels while the vehicle is not moving (torque converter & clutch)

3. What Does a Transmission Do?
The basic purpose of a transmission breaks down into 3 parts
Ability to alter shaft RPM
Ability to multiply torque
Ability to reverse the direction of shaft rotation

4. How Does the Transmission Produce Torque Multiplication And/or RPM Reduction
Transmissions use gears
Spur
Helical
Planetary
Gears are able to change the RPM and the torque of the power moving through the transmission as well as the direction of rotation

5. How Stuff Works
Planetary Gears
                                                                                                                                                

6. Helical Gears

7. Spur Gears

8. Types of Gears Spur Helical Planetary Simplest gear design
Straight cut teeth
Noisy operation
Helical
Spiral cut teeth
At least two teeth are in mesh at any time
Distributes the tooth load
Quieter operation
Planetary
Most complex design
Used in almost all automatic transmissions
Contains three parts
Sun gear
Planet gears
Internal gear (ring gear)
Types of Gears

9. Power Vs. Torque Torque – measurement of twisting force
How Stuff Works
Power Vs. Torque
Torque – measurement of twisting force
Power – measurement of how quickly work can be done
Power is dependent on torque and RPM
Horsepower = Torque x RPM
5252
Mustang Cobra VS. Caterpillar Diesel

10. Gear Ratios When two gears are in mesh, a gear ratio exists
How Stuff Works
Gear Ratios
When two gears are in mesh, a gear ratio exists
Driven Gear = Ratio
Example:
Drive gear has 14 teeth
Driven gear has 28 teeth
28  14 = 2:1 ratio (two to one ratio)
The drive gear must rotate twice to make the driven gear rotate once
Drive Gear

11. Reversal of Direction
When two gears are in mesh one will spin the opposite direction of the other
Idlers are used to reverse direction

12. Speed Change
The change in RPM from the input gear to the output gear is directly proportional to the gear ratio
Example: 3:1 gear ratio
Input gear turns at 900 RPM
Output gear turns at 300 RPM

13. Torque Multiplication
The change in torque from the input gear to the output gear is directly proportional to the gear ratio
Example: 3:1 gear ratio
Engine turns input gear at 900 RPM with 50 lb/ft of force
Output gear turns driveshaft at 300 RPM with 150 lb/ft of force

14. Torque Multiplication
1 inch inches

15. Multiple Gear Ratios
Individual gear ratios can be multiplied to calculate a total gear ratio
Example: Chevy caprice with a TH-350 transmission and a 305 engine
By removing the differential cover and inspecting the gearset you are able to count 10 teeth on the input gear and 41 teeth on the output gear
41  10 = 4.1:1
You are able to find the 1st gear ratio of the TH-350 in a manual which is listed as 2.52:1

16. Multiple Gear Ratios
Rear end ratio x 1st gear ratio = total gear ratio
4.1 x 2.52 = 10.33:1
This tells us that the engine turns revolutions for every 1 revolution of the tires (speed reduction)
Torque multiplication can also be calculated
The 305 engine produces 245 lb/ft of torque at 3200 RPM
@ 3200 RPM in 1st gear the torque acting on the rear tires = 230 lb/ft x = lb/ft torque !!!

17. 1 200 ft/lbs 2000 RPM 4:1 800 ft/lbs 500 RPM Underdrive 2 2:1
Gear
Engine Output Torque
Engine Speed
Gear Ratio
Transmission Output Torque
Transmission Output Speed 1
200 ft/lbs
2000 RPM
4:1
800 ft/lbs
500 RPM
Underdrive 2
2:1
400 ft/lbs
1000 RPM 3
1:1
Direct Drive 4
.5:1
100 ft/lbs
4000 RPM
Overdrive

18. Automatic Transmission I.D.
Most automatics are identified by the oil pan.
Look at the shift indicator to determine if the transmission is a 3-speed, 4-speed etc.
Different transmissions may have been installed in otherwise identical vehicles.
Shopkey and other manuals list transmission application by vehicle.

19. Automatic Transmission I.D.

20. Automatic Transmission I.D.
GM I.D. 1
Aluminum Powerglide
14 bolts 2
TH200 Metric
11 bolts 3
TH350
13 bolts 4
TH400 5
TH200-4R
16 bolts 6
TH700-R4, 4L60, 4L60E 7
4L80E
17 bolts

21. Planetary Gearsets Simple planetary gearsets contain three components
Internal (ring) gear / (annulus gear)
Planet gears (and carrier)
Sun gear
One component will be the drive member, one the driven, and one will be held (except direct drive and neutral)
Unlike other types of gears, planetary gears are able to operate on one single axis

22. Planetary Action Direct Drive Any two of the components are driven
1:1 Ratio

23. Planetary Action Underdrive Planet carrier is the output
Minimum reduction
Ring gear is held
Sun gear is the input
Maximum reduction
Ring gear is input
Sun gear is held

24. Planetary Action Overdrive Planet carrier is the input
Minimum overdrive
Ring gear is the input
Sun gear is held
Maximum overdrive
Ring gear is held
Sun gear is the input

25. Planetary Action Reverse Planet carrier is held Underdrive Overdrive
Ring gear is the output
Sun gear is the input
Overdrive
Ring gear is the input
Sun gear is output

26. Sun Carrier Internal Speed Torque Direction Input Output Held
Maximum Reduction
Maximum Increase
Same as Input
Minimum Reduction
Minimum Increase
Reduction
Increase
Opposite as Input

28. Calculating Planetary Gear Ratios
Direct Drive = 1:1
Underdrive
Carrier is output
# of sun gear teeth + #of ring gear teeth
= Ratio
# of teeth on the driving member

29. Calculating Planetary Gear Ratios
Overdrive
Carrier is input
# of teeth on the driven member
= Ratio
# of sun gear teeth + #of ring gear teeth

30. Calculating Planetary Gear Ratios
Underdrive
Carrier is held
# of teeth on driven gear
= Ratio
# of teeth on driving gear