Isuzu M-150 (77.5 mm) 4-Speed

1. Being sure snap ring is fitted to mainshaft rear bearing, install bearing into center support with snap ring side turned rearward.





2. Using an arbor press, install mainshaft into bearing which has been fitted into center support. When installing mainshaft, care should be taken so as not to damage reverse block dowels fitted to center support.

3. Install 4th blocker ring, needle roller bearing, and drive gear shaft.

4. Install countershaft to center support,then install rear bearing outer race to countershaft from rear side of center support.

5. Install bearing retainer to center support. Clean threaded hole in center support, apply suitable sealer to screw threads, install screws, and torque to 15 ft. lbs.

6. Engage synchronizers in lock and place center support in transmission case temporarily.





7. Install reverse gear, washer, and spring washer to rear end of
countershaft and torque nut to 80 ft. lbs. Install reverse gear so that teeth with rounded edges are turned rearward.





8. Install reverse gear to mainshaft with rounded teeth turned rearward and torque nut to 95 ft. lbs., then stake nut to mainshaft.

9. Remove case from center support.





10. Lubricate and install two interlock pins to center support.





11. Noting direction of installation, install shift fork to synchronizers.





12. Install 3rd/4th shifter shaft to center support and shift fork, then bring shaft into neutral position. Install 1st/2nd shifter shaft and reverse shifter shaft to center support.

13. Supporting end of shaft with piece of wood, drive spring pin to 1st/2nd and 3rd/4th shift forks.





14. Install three detent balls and springs into holes in center support, then install gasket and plate and torque bolts to 15 ft. lbs. The reverse spring is shorter than the others.

15. Install gasket to transmission case and install center support by aligning it with dowels on case. Avoid hitting support or case during installation.

16. Install retaining rings to drive gear shaft and countershaft bearing outer races.

17. Assemble reverse shift block, reverse block, and reverse shift fork using pins and snap rings.





18. Install shift block assembly to reverse shift fork, then insert shift fork into groove in reverse idler gear. Install gear to idler shaft and reverse shift block to shifter shaft.

19. Tighten reverse block retaining bolts.

20. Secure reverse shift block to shifter shaft by driving spring pin with suitable tool.

21. Insert clip end into hole in mainshaft and install speedometer driven gear.

22. Install gasket to center support, then install extension housing to support by aligning it with dowels and torque bolts to 30 ft. lbs.

23. Install back-up light switch.

24. Install gasket to upper face of extension housing and install shifter cover.

25. Install speedometer driven gear and ball stud.





26. Install gasket to transmission case, then install front bearing retainer. Apply suitable sealer to bolt threads on lower side before installation and torque bolts to 15 ft. lbs.

27. Install bearing, boot, and clutch fork.

28. Install gearshift lever to shifter cover temporarily and check for smooth and correct operation.