N.W.Geeson I.Eng. M.I.R.T.E M.S.O.E (VER 2.JAN 2010)
GeneralUnless stated otherwise. References to Bentley MKVI should be taken to include Bentley R Type Continental, Bentley R Type, R-R Silver Dawn and Silver Wraith SWB. References to Bentley SI, include Bentley SI Continental and R-R Silver Cloud I. References to Bentley S2 or S3, included Continental Models and R-R Silver Cloud II / III. Most of the images used in this article and the text description refer to the Silver Dawn Bentley R Type rear axle however the principle is identical with all rear axles to which this article refers. Axles fitted to all Silver Clouds and Bentley equivalents use UNF or UN Special threads and therefore the appropriate UNF wrench sizes will need using. It should be noted that the axle drive flange bolt pitch circle and sizes of the four retaining nuts and bolts are very slightly different between Silver Dawn /Bentley R Type axles and later Silver Cloud / Bentley S type axles. However in respect of the drive flange removal tool the flange differences are so small that the same puller will suffice on all the drive flanges.
Oil leaks, Checks, Drain and Breather
A rear axle pinion seal oil leak may appear self evident but it is advisable to carry out a few checks before tearing down the front of an axle to replace the oil seal.
Firstly all chassis with a working lubrication system will have some evidence of oil around the rear axle. Depending upon how often the chassis oil pump has been used and the relative car speeds attained, either oil mist, or heavier oil deposits will have collected around the axle case.
Secondly, due to the axle oil sealing arrangement, or truthfully lack of it, some oil may be evident on the left hand side of all axles, or egressing from the axle tube drain. As long as these are minor drips compared with out and out leaks, there is no need for concern.
In the worst oil leaking situation the oil will be seen to readily drip from the oil seal housing just behind the axle drive flange, as shown in Fig 1.
If in doubt make sure the oil level is up to the full mark by unscrewing the 17/32nd hexagon filler plug and checking that the oil is level with the inside of the filler orifice. At that point make sure the front wheels are blocked and raise the rear wheels off the ground as far as possible. After a short period any faulty oil seal will be apparent when oil flows out of the seal housing. This exactly replicates the situation of a car parked facing downhill, and the speed of the oil flowing out of the axle will quickly show how many of these axles are ruined by lack of oil.
At this point many owners may decide to bite the bullet and fit a modern oil seal, but first check the condition of the pinion bearing(s). It is of no use renewing or converting the oil seal if the bearings are sloppy and worn. This article does not deal specifically with renewing the pinion bearings but some thought needs applying before attempting renewal of pinion bearings in 60 year old axles.
Often owners take advantage of the situation when changing an oil seal to change the axle oil. In this connection a few words of warning on a subject, that even catches out some specialists.