Manual - Chapter 3 Gearbox

4. Gearbox: removing and refitting the bearings and seals

  1. All oil seals should be renewed as a matter of course whenever they are disturbed and especially if they show any signs of leakage or of damage.
  2. Using a socket or similar as a drift, tap out the seal from the inside outwards; note first which way round the seal is fitted and at exactly what depth. In the case of the output shaft front sealing plug, this will mean that the oil guide must be removed as well; do not forget to clean it and install it with the protruding spout projecting inwards (to the rear) before fitting a new sealing plug. Where seals cannot be driven out from behind, eg input shaft rear end seal or gearchange shaft seal, they must be levered out using a tool with rounded edges, taking great care not to scratch or damage the seal housing.
  3. To fit new seals, find a socket spanner or similar tube which bears only on the seals hard outer edge and use this to position the seal squarely in the mouth of its housing. Apply a thin smear of grease to the seal outside edge and tap it into place until it is flush with its surrounding housing or, in cases such as the output shaft rear seal, until it seats on a locating shoulder. Seals should be installed with the manufacturer's marks facing outwards, ie with the spring-loaded centre lip towards the fluid or gas being sealed. Note that the shaft rear seal, therefore is installed with the centre lip outwards, ie to the rear. If rotation arrows are found, the seal must be installed so that these face in the normal direction of rotation of the shaft.
  4. All gearbox ball bearings should be easily removed with their shafts. If this is not the case, or if taper roller bearing outer races are to be removed, heat the casting evenly in an oven or similar to 100 °C (212 °F) and tap it firmly down on to a clean, flat wooden surface; this should dislodge the bearings or bearing outer races easily. Take great care to prevent any risk of personal injury when healing components or handling heated components. Note carefully the presence and number of any shims behind any of the bearings. Remember also to renew any seals that may have been left in place; the heat will almost certainly damage them.
  5. If any of the shafts or bearings are renewed, or if the tolerances are found to be incorrect, the shim thicknesses must be adjusted. Before any bearings or seals are refitted, refer to Section 7 of this Chapter.
  6. Ball bearings are refitted to their shafts using a hammer and a tubular drift such as a socket spanner, which bears only on the bearing inner race. Drive each bearing down its shaft until the inner race contacts the locating shoulder or other component against which it must rest.
  7. Input shaft taper roller bearings are fitted in a similar manner but must be heated first to approximately 80 °C (176 °F) before they can be fitted. The front bearing must be driven down to rest against shims placed against the shaft front flange and the rear bearing must be driven along the shaft until the retaining circlip can be refitted in its groove; the bearing must then be pulled back against the circlip to locate it.


4.1 Oil seals should be renewed as a matter of course - remove and refit as described in text

4.2a Note correct fitted position ofoutput shaft oil guide

4.2b Be careful not to damage seal housing when levering seals out.....

4.3 .....and note how seal is fitted so that the new component can be correctly installed