Manual - Chapter 3 Gearbox

5. Gearbox shafts: dismantling and reassembly

Input shaft

  1. Before the input shaft can be dismantled some means must be devised of compressing safely the shock absorber spring. On the machine featured in the accompanying photographs a knife-edged bearing puller was assembled on the shaft rear end with its edges pulling against the shock absorber front cam. This relieved spring pressure enough for the retaining circlip to be removed and the shaft rear bearing to be drawn off using another puller.
  2. Gradually release spring pressure by unscrewing the compressing tool until the spring is at full extension (43 mm/1.7 in on the machine featured) and its pressure is released.
  3. Dismantle the compressor and withdraw the rear cam, the front cam, the spring and the spring seat. If the front bearing is to be renewed, draw it off using one of the pullers and note the presence and number of any shims fitted between it and the shaft collar. Do not forget to renew the bearing outer race at the same time. See Section 4. 4 On reassembly, lubricate the shaft splines and fit the spring seat, the spring, the front cam and the rear cam. Clamp the shaft front end in a vice with soft jaws so that the shaft is held securely upright but cannot be marked or damaged. Obtain a new circlip as a safety measure; re-used circlips can occasionally fail in service.
  4. BMW recommend that the bearing is heated to approximately 100 °C (212 °F) to permit refitting but this was found in practise to be unnecessary. Although the bearing was a tight fit it was possible to refit it using a hammer and a long tubular drift which bore only on the inner race. Drive the bearing down until it contacts the shoulder, at which point the circlip groove should be exposed. Fit the new circlip and use a bearing puller to draw the bearing back into contact with it. Note, there must be no clearance between the bearing inner race and the circlip or the preload setting will be incorrect.
  5. BMW recommend the input shaft front bearing be heated to approximately 80 °C (176 °F) before it can be installed. Whether this actually proves necessary or not it is essential that the correct size shim is placed against the shaft collar and that the bearing is driven down the shaft, using a tubular drift which bears only on its inner race, to rest firmly against the shim and collar. See Section 7.

Layshaft

  1. If it is necessary to renew the layshaft bearings they can be removed and refitted using respectively a knife-edged bearing puller and a hammer and tubular drift of suitable size, as described above. If it is found to be faulty in any other way, the shaft must be renewed complete.

Output shaft

  1. Use a knife-edged bearing puller or similar to remove the bearing from each end of the shaft, then remove the various gear pinions with their bushes or needle roller bearings, using circlip pliers to release the retaining circlips, where fitted.
  2. BMW recommend that the 1st gear pinion centre bush must be heated to approximately 80 °C (176 °F), to permit removal, using a puller bearing on the 4th gear pinion; in practice the bush was found to be a fairly slack fit and could be pulled off by hand.
  3. Ensure that all components are stored exactly as they are removed so that they can be refitted the same way round and in the original sequence. If in doubt, refer to the photographs and illustration accompanying the text.
  4. On reassembly, lubricate all components, and renew any circlips which appear to be distorted, damaged or worn. The accompanying series of photographs show the rebuilding of an output shaft assembly; use this if in any doubt about the fitting or location of any component.

 

Fig 3.3 Gearbox shafts


5.1 Note method used to compress shock absorber spring before removing or refitting input shaft rear bearing


5.3 Input shaft shock absorber can be easily dismantled once rear bearing is removed


5.4 Fit spring seat, spring and shock absorber as shown - note shoulder and circlip groove on shaft rear end


5.5 Rear bearing should be tapped down to shoulder until circlip can be fitted, and then drawn back against circlip tp produce correct installed length


5.8 Use bearing puller as shown to remove shaft bearings


5.9a Fit shim and 5th gear pinion centre bush to output shaft as shown.....


5.9b .....followed by the 5th gear pinion and a second shim, and the rear bearing.....


5.9c .....which is fitted as shown to rest against the centre bush and shim


5.10a Fit the 3th gear pinion as shown over the shaft front end followed by a circlipand a splined thrust washer


5.10b 2nd gear pinion rotates on a split-cage needle roller bearing


5.10c Fit th 2nd gear pinion as shown.....


5.10d .....pinion is located by a splined thrust washer and secured by a circlip


5.11a Fit 4th gear pinion as shown, followed by shim and 1st gear pinion centre bush


5.11b Fit 1st gear pinion as shown, followed by.....


5.11c .....shim and shaft front bearing


5.11d Note method used to refit gearbox bearings to shafts