Pinion Adjustment

Pinion Adjustment

The pinion bearing preload adjustment depends on the type of spacer used to hold the bearings apart. Two main arrangements using a rigid spacer and a collapsible spacer are illustrated in Fig. 26.40.

A bearing arrangement with a rigid spacer has a series of shims to control the static load on the bearings (Fig. 26.40A). On this arrangement the pinion nut is fully tightened before the preload is measured and shims are either added or removed if found incorrect. With this typeof spacer, the renewing of the pinion oil seal is simplified, because the seal replacement does not alter bearing preload provided the pinion nut is fully tightened

Fig. 26.40. Pinion bearing adjustment

The use of a collapsible spacer (Fig. 26.40B) saves time on the preload operation. While holding the bearings in alignment, this ductile steel spacer collapses under-pressure from the pinion nut so that the preload can be set in one operation. With the pinion, bearings and seal in position, the nut is tightened only sufficiently to provide the recommended preload. When the torque is correct, the nut is locked in position. Since a ductile material has very little elasticity, if the bearing preload is too high a new spacer is necessary.

More care is necessary with units using a collapsible spacer when a pinion seal is replaced to arrest an oil leak. Before unlocking the nut, the precise position of the nut relative to the pinion must be observed. If this is done, the crown wheel has to be removed for preloading the pinion bearings. Pinion position relative to the crown wheel must be set accurately for correctly positioning the apex point of the pinion. Otherwise, noise, in the form of a 'whine', and possible breakage of the gear teeth is likely to happen. In the earlier days, the initial position of the pinion was set by aligning it with the edge of the crown wheel teeth. Nowadays, for this operation a special 'dummy pinion'jig is used.