Manual - Chapter 3 Gearbox

3. Gearbox: dismantling

  1. Unscrew the neutral detent plug and tip out the coil spring and ball behind it. Remove the gear position indicator switch from the rear cover.
  2. Unscrew the front cover retaining screws, then withdraw the front cover; a loud click will be heard as the detent roller arm slips off the selector cam. BMW recommend that the cover is heated evenly, in an oven or similar to 100 °C (212 °F) to permit removal but it was found in practice that this was not necessary; although the cover was a tight fit, as soon as the retaining screws were removed a few taps on the input and output shaft ends with a soft-faced mallet broke the seal so that the cover could then be pulled off with the aid of a few further taps. Note the provision of a leverage point at the bottom right-hand (gearbox in position on the machine) 'corner' of the front cover; this is provided so that a screwdriver can be inserted to exert sufficient leverage to break the initial seal. Do not force the screwdriver (or any other tool) between the machined sealing surfaces, and do not. exert excessive pressure to release a stubborn cover or it may crack.
  3. As soon as the cover is removed, check inside the bearing locations and note exactly the presence and number of any shims that may be fitted. These shims must be clearly labelled so that they can be returned to their original locations on reassembly. Note also the two locating dowels in the mating surface.
  4. Withdraw the selector fork shafts and place them in separate, clearly-marked containers; while they are identical when new they must not be confused when part-worn or the mis-matching of part-worn components will cause greatly accelerated wear. Rotate all three selector forks away from their drum tracks.
  5. Press back the selector claw arm and lift out the selector drum; a very light tap on its rear end with a soft-faced mallet will dislodge it if it proves stubborn. The cam and pins can be withdrawn from the drum if required.
  6. Noting the presence of the separate rollers around their guide pins, remove and place in separate, clearly-marked containers the selector forks. As each fork is removed use a spirit-based felt marker or similar to mark its top (or front surface).
  7. Holding them together as a single unit, pull out the layshaft and output shaft. BMW recommend that the housing is heated evenly, in an oven or similar, to approximately 100 °C (212 °F) to permit shaft removal but again this was found not to be necessary in practice; a firm tap on the output shaft rear end from a soft-faced mallet proved sufficient to dislodge bath shafts. With these removed the input shaft can be withdrawn. Check that there are no shims fitted at the shaft rear bearings.
  8. To dismantle the selector mechanism, first prise off the black plastic cap from the gearbox breather then use a hammer and a suitable drift to tap out the breather sleeve from the inside; take care not to deform the sleeve.
  9. Withdraw the circlip from the claw arm mounting guide rod and push the guide rod upwards and out through the breather orifice. Withdraw the claw arm and mounting; if desired the two can be separated by removing the retaining circlip from the claw arm pivot. Note how the spacer fits inside the loop of the claw arm spring.
  10. Unscrew the tapered grub screw from the gearchange pedal shaft and withdraw the shaft; note the shim between the return spring and the housing wall. Displace the two circlips and withdraw the locating plate with the selector lever and return spring and the shim. If the gearchange pedal is to be removed from the shaft, first mark the shaft end next to the split in the lever so that the lever can be refitted in the same position.
  11. The detent roller arm can be withdrawn from the front cover by lifting its return spring straight end over the cover stop lug to release the spring pressure and then removing the retaining circlip to release the arm. The roller can be removed and refitted after its retaining circlip has been withdrawn. Drive out from the inside the small plug which seals the passage next to the detent roller arm.

 

Fig3.1 Gearbox Housing


3.1 Unscrew detent plug to release neutral detent assembly