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

3. 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 1:1 ratio of high gear • Planetary gears • Automatic transmission with lock-up torque converter

7. 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

8. 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

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 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

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