Gears and Transmissions

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. Types of Gears • Spur • 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)

6. 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

7. 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

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

9. 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

10. 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

11. Torque Multiplication 1 inch 3 inches

12. 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

13. 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 10.33 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 10.33 = 2375.9 lb/ft torque !!!

15. 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.

16. Automatic Transmission I.D.

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

18. 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

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

20. 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

21. 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

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

25. 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

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

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