N.W.Geeson I.Eng. M.I.R.T.E M.S.O.E (VER 2.JAN 2010)
Background and the problems arisingRear wheel bearing failure on these cars can be a nerve racking experience besides being expensive. This type of failure is becoming very frequent and is also affecting the later Silver Cloud cars. In a recent 18 month period I have known of no less than 19 rear wheel bearing failures.
All of the axle bearings and rear wheel bearings on the cars prior to about June 1952 are METRIC. Although the service manual dimensions are shown in imperial equivalent sizes the bearings are true metric. Only when the rear axle pinion bearings were changed to taper bearings circa June 1952 did the pinion bearings change to imperial. However the axle side bearings and the rear wheel bearings remained Metric, as did one of the axle side bearings during the reign of the Cloud cars.
The original wheel bearings had a special inbuilt end float and the service manual warned against renewing the bearings just because the end float was present. Unfortunately this bearing end float allows the half shaft splines to also try to end float in the splined bevel wheels. Readers who are in the automotive engineering field will realise that splined shafts resist end float when under driving conditions, but when the splines do slide, they wear the half shaft splines. When the shafts do not slide, they transfer the end load directly onto the axle bevel gear thrust washers.
The rear wheel bearings are about the last components that need renewal on these cars, long after the engines have worn out, however after some 50 years the bearing grease is almost non existent and what remains is not a good lubricant. Even attempting to re-grease the bearing provides no guarantees as the cage separating the ball bearings is worn and breakage of this cage is one reason for these bearings locking up without warning. Re-greasing a bearing after a considerable period of time, without doubt, will appear to make the bearing revolve smoother. It does not however replace metal that has worn off the bearings and which is captured in its granulated state within the sealed bearing. Metal, which given time will guarantee a collapsed bearing but no guarantee is given as to whether the affected car stays on its four wheels. It is a fair certainty that the sunroof panel will eject if the car slides on its roof; if it happens to your car it gets no rosettes as this trick has been performed before. The only decision you have to make is whether your life and others are worth the cost of the bearings.
Persistent running with slack and partially failed rear wheel bearings will eventually cause the bearing to turn on the half shaft and within the bearing housing. Usually not realised, although I earn my semi-retired living from the results, is that failed rear wheel bearings are one cause of failure of the main axle bearings and in fact scrapping of both the main axle case and the inner differential gear case. Turning the subject on its head, the failure of the axle side bearings will, and does, fail the rear wheel bearings. Each set of bearings support the half shaft at either end, actually indirectly through a bevel gear at the inner end, so a complete bearing failure at one end affects the other end.