Chapter 8 Manual Transmission Construction and Operation 175 Copyright by Goodheart-Willcox Co., Inc. 1. Clutch control shaft 2. Transmission case 3. Main drive gear 4. Synchronizer (3-4 speed) 5. 3rd speed gear 6. 2nd speed gear 7. Synchronizer (1-2 speed) 8. 1st speed gear 9. Rear bearing retainer 10. Synchronizer (reverse and overdrive) 11. Overdrive gear 18. Counter reverse gear 19. Reverse idler gear 20. Reverse idler gear shaft 21. Counter overdrive gear 22. Extension housing 23. Speedometer drive gear 12. Control shaft 13. Control lever 14. Front bearing retainer 15. Countershaft gear 16. Under cover 17. Mainshaft 1 3 4 5 6 7 8 9 10 11 12 13 2 14 15 17 18 19 20 16 21 22 23 6-Speed Transmissions The 6-speed transmission has six speeds (gear ratios) in a compact case. In some instances, both fifth and sixth gears are overdrives. The linkage is usually internal. A 6-speed is often used with high-performance engines to obtain high performance while maintaining acceptable gas mileage. Dual-Clutch Transmissions and Transaxles Many vehicles are using dual-clutch transmissions and transaxles. The easiest way to understand a dual-clutch trans- mission or transaxle is to think of it as two separate transmis- sions in a single housing. Figure 8-38 shows the arrangement of one type of dual-clutch transmission with two separate clutch assemblies. Dual clutches were discussed in Chapter 6. Note the inner and outer transmission input shafts. Each shaft is attached to a different clutch. The shafts are splined to gears that mate with the single output shaft. There are three odd numbered transmission gears (first, third, and fifth), and two even numbered output gears (second and fourth). Although not shown here, another gear would be installed to provide reverse. An actual transmission would also have shift forks and synchronizer assemblies. Shift Sequence—Upshifts The following series of illustrations show how the dual- clutch transmission upshifts through various gears. Refer to each illustration as you read the accompanying text. In Figure 8-39, the transmission is in first gear. The first gear is being driven by the odd gear clutch. As the vehi- cle is accelerated, the second gear is engaged, but because the even gear clutch is not applied, it is ineffective. To obtain second gear, the odd gear clutch releases and the even gear clutch applies, as shown in Figure 8-40. Since Figure 8-37. The 5-speed resembles the 4-speed transmission. Fifth gear is usually an overdrive. In some instances, overdrive has been added to a 4-speed by extending the countershaft gear assembly and transmission case. An extra gear is also added to the output shaft. Figure 8-38. An arrangement of the major parts of a typical dual-clutch transmission. For clarity, shift forks, synchronizer assemblies, and clutch activating mechanisms are not shown. Crankshaft Output shaft Even gear clutch Odd gear clutch 2 4 5 3 1 Inner input shaft Outer input shaft