Manual - Chapter 3 Gearbox

6. Gearbox: examination and renovation

  1. Thoroughly clean all components removing all traces of dirt, corrosion, old oil and other foreign matter. Check that the front cover sealing surfaces are clean, flat, and free of old jointing compound.
  2. Check the housing and front cover for cracks, damage or other faults such as damaged threads. Most faults of this sort can be repaired but such work is usually for the expert, a good authorised BMW dealer should be able to recommend such an expert, depending on the nature of the fault.
  3. Examine each of the gear pinions to ensure there are no chipped, rounded or broken teeth and that the dogs on the ends of the pinions are not rounded. Worn dogs are a frequent cause of jumping out of gear; renewal of the pinions concerned is the only effective remedy. Check that the inner splines are in good condition and the pinions are not slack on the shafts. Bushed pinions require special attention in this respect, since wear will cause them to rock.
  4. Check both the input and the output shafts for worn splines, damaged threads and other points at which wear may occur, such as the extremities which pass through the bearings. If signs of binding or local overheating are evident, check both shafts for straightness.
  5. Examine the selector forks to ensure they are not twisted or badly worn. Wear at the fork end will immediately be obvious; check each claw end in conjunction with the groove with which it normally engages Do not overlook the roller which engages with the selector drum groove; this is subject to wear.
  6. Note: If any wear or damage is found on the selector drum, selector forks or the gearchange pedal arm, do not attempt any sort of repairs involving the use of heat. These components are made trom a special light alloy which may well react strongly if heated excessively. It is recommended that all of these components are renewed if they are found to be worn or damaged.
  7. Check the remaining selector components for damage or wear. Check that all are straight and that there is little or no wear at the various points of contact. Renew any worn or damaged component.
  8. As previously stated, all oil seals should be renewed as a matter of course whenever they are disturbed.
  9. Wash the bearings thoroughly in a high flash-point solvent. Do not pull bearings off their shafts if they can be cleaned and checked in place. Do not 'spin' a dry bearing. If any radial play is evident. or if the bearing feels rough when turned, it should be renewed. Examine the inner and outer races and the balls or rollers for damage. Renew any bearing that is showing the least sign of pitting or discoloration on any of its tracks or elements.
  10. Any circlips that were disturbed during the course of dismantling should be examined closely and renewed if there is the slightest doubt about their condition. If any are a slack fit on their shafts they must be renewed as a matter of course.
  11. Similarly the various springs in the selector mechanism should be renewed if there is any doubt about their condition. Unless they are actually damaged, in which case renewal should be automatic, it is difficult to assess whether springs are fatigued or not.