Manual - Chapter 3 Gearbox

8. Gearbox: reassembly

  1. All components should be completely clean and renewed or repaired as necessary. All bearings or bearing inner races should be installed correctly on their respective shafts and all oil seals, oil guides and taper roller bearing outer races should be installed in the housing or front cover, as appropriate.
  2. Refit the detent roller arm and secure it with its circlip, ensuring that its spring is fitted as shown in the accompanying photograph.
  3. Refit the gearchange pedal to the shaft using the mark made on removal to ensure that the pedal is correctly positioned. Tighten the pinch bolt securely.
  4. Fit the return spring and the locating plate to the selector lever as shown in the accompanying photograph and fit the assembly to the housing; do not forget the shim between the spring and the housing wall. Refit the two retaining circlips. Grease the gearchange pedal shaft and refit it, taking care not to damage the lips of the shaft oil seal. The shaft will fit only one way if the tapered grub screw is to lock it correctly to the selector lever; ensure that the two are correctly aligned, apply a few drops of Loctite 242 or similar thread-locking compound to the screw threads and refit it, tiqhteninq it securely. Use the torque wrench setting, where specified.
  5. Fit the spacer and claw arm spring to the claw arm, ensuring that the spacer fits inside the spring loop. Fit the assembly to the claw arm mounting and secure it by refitting the pivot retaining circlip. Position the claw arm mounting and rein the guide rod and its circlip to retain it. Tap the gearbox breather sleeve into its orifice, but be careful not to drive it so far in that the black cap rests on the gearbox housing. Refit the black plastic cap to the breather sleeve.
  6. Install the input shaft in its rear bearing; lubricate both bearings with the specified oil.
  7. Lubricate their bearings, bearing surfaces and all other points of contact, then mesh together the gear pinions of the layshaft and output shaft assemblies and insert the two as a single unit. Rock the input shaft away from the layshaft until its bearing is clear of the layshaft gear pinion teeth. Press the layshaft and output shaft into position and straighten the input shaft.
  8. Note that If the shaft bearings will not fit easily into the housing locations the housing must be heated evenly, in an oven or similar. to approximately 100 °C (212 °F) to permit this. If this is found to be necessary first remove all components which might be damaged by the heat and take great care to prevent any risk of personal injury when heating components or when handling heated components.
  9. Check that all three shafts are free to rotate. then install the selector forks using the marks or notes made on dismantling to identify each fork and which way it is fitted. If no marks were made, proceed as follows:
  10. The first fork to be refitted is to the output shaft 3rd gear pinion groove; this actually selects 5th gear and is the widest across the claw ends of the three forks. It is fitted with its guide pin towards the front of the gearbox housing; this will engage the selector drum rear groove.
  11. The next fork selects 3rd and 4th gears and is fitted to the layshaft sliding gear pin ion groove; its guide pin will engage the selector drum centre track. It is the narrowest across the claw ends and can be identified by its long neck. It is refitted with its guide pin towards the rear of the gearbox housing.
  12. The last fork selects 1st and 2nd gears and is refitted with its guide pin towards the rear of the gearbox housing, to engage the selector drum front groove. Of medium width across the claw ends, it is fitted to the output shaft 4th gear pinion groove.
  13. Swing all three forks as fa, as possible away from the selector drum and refit the separate roller to each fork's guide pin; retain the roller with a dab of grease.
  14. Fit the five selector pins and the small locating pin to the selector drum front end, refit the selector cam aligning its keyway with the locating pin and insert the drum assembly, pressing back the claw arm to permit this.
  15. Rotate the drum until the cam neutral detent recess is approximate!y in the 12 o'clock position from the drum centre, ie in the neutral position. Swing the forks back into contact with the drum, engaging each fork's guide pin roller mits respective drum groove. Lubricate and refit the selector fork shafts, ensuring that each is pressed fully home in its original location.
  16. Ensuring that the correct number and thickness of shims are used, refit the output shaft and layshaft shims to their respective bearing housings in the front cover. Press the shims fully into place and use grease to retain them.
  17. Referring to the accompanying photograph make up a stop trom a suitably-sized rod (a convenient bolt was used tor the photograph, with a flat ground on one side to ensure that it would not slip) or similar to hold the detent roller arm clear of the selector drum cam while the front cover is refitted. Apply a thin smear of Loctite 573 or similar jointing compound to the degreased mating surfaces. Make a final check that all components have been refitted and that all shafts are free to rotate.
  18. BMW recommend that the front cover is heated evenly, in an oven or similar, to approximately 100 °C (212 °F) to permit refitting. This was found not to be necessary since the cover could be removed and refitted quite easily by hand. If it is necessary to heat the cover, take great care to avoid the risk of personal injury when heating components or when handling components that have been heated. Remember also to remove first components such as oil seals which will be damaged by the heat, and to place the shims on the bearings, not in the front cover bores.
  19. Press the cover into place, then refit and tighten to the specified torque setting the cover retaining screws. Pull out the roller arm stop; a distinct click should be heard as the arm contacts the cam.
  20. Rotating the input shaft, and if necessary the output shaft, check that the shafts rotate smoothly and that all gears can be selected with reasonable ease. If all is well, drift the locking plug into the small orifice drilled next to the detent roller arm pivot.
  21. Refit the ball and spring of the neutral detent assembly, apply a few drops of Loctite 242 or a similar thread locking compound to its threads, and refit the neutral detent plug, tightening it to the specified torque wrench setting.
  22. Refit any oil seals which have not yet been installed, and install the gear position indicator switch on the gearbox housing rear face; do not overtighten its retaining screws or the switch may crack. Position the switch carefully so that the cutaway section of the selector drum shaft aligns with that of the switch rotor.