Rear axle pinion oil seal renewal and modification
Applicable to all early post war cars up to and including Silver Cloud III / Bentley S3, but excluding all Phantom axles
N.W.Geeson (Copywright 2005-2006-2007-2008-2009)
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Two bolts approximately 1.50 inch long and 0.375 diameter, with any suitable thread, and four nuts and four plain washers will also be needed. A large, preferably flat tyre lever or similar will be required to bridge the bolts eventually as shown in Fig 11.
A heavy hammer of around 1.75 Kgs will be needed to strike the end of the puller.
Previously the problem of removing the drive flange without distorting it any more than it may have already been damaged was mentioned. You don’t want to bend it anymore because you definitely do not want to know the new price! The way to overcome the problem is to make a thick block puller similar to that shown in Fig 9 and fitted to the drive flange in Fig 10. A block of metal is used circa 1.25 inch thick. Notice in Fig 9 that there is quite a large diameter central relief around the puller screw. This relief is required to accept the slight protrusion above the flange face of the axle pinion shaft end and the flange retaining nut that stands proud of the flange face, when the tool is coupled as in Fig 10. This particular puller has been constructed from an old Ford rear hub puller which has the added advantage that it can be used as a pinion housing extractor by using it as a hammered extractor on its outer flange. The required pitch holes for drilling purposes are shown in Fig 8. As long as the block is firmly bolted to the axle drive flange first to prevent flange distortion, a three leg puller might be used to extract the flange together with the block, but a more permanent and useful puller can be made with a little more work.
Parts and Misc
Assuming that all the machining is being done in a machine shop it would be sensible to perhaps consider having them fit the new oil seal. Otherwise it will be necessary to find or make a tool to drive the new oil seal into position. The tool diameter will depend on which oil seal size is due to be fitted, see sizes in Fig 7.
An oil seal, together with a drive shaft lock tab, and perhaps a spare of each, and a quantity of gasket sealer will be needed as a minimum. Oil seals and lock tabs can easily be damaged in this exercise, and is the reason for suggesting obtaining spares.
Gaining access to the oil seal
The axle drive flange must be removed to gain access to the oil seal housing.
Mark the corresponding flanges on the axle flange edge and propeller shaft so that they can be eventually matched up correctly. Using the hand brake to lock up the propeller shaft at the required indexing positions, undo and remove the four nuts, special grover spring washers and bolts. The nuts are a special tight fit so be careful to use good tight fitting wrenches and do not round off the nuts corners. Observe that the square heads of the bolts are only just held from rotating and it is wise to hold the bolt heads to prevent damage to the rear of the flange.
Once the bolts are removed detach the shaft and immediately examine the shaft coupling flange and in particular the locating ring that locates in the groove marked ‘ A’ in Fig 12. Ensure that the machined locating ring is not distorted and will engage the axle drive flange correctly. Before proceeding further check the drive shaft mating face with a straight edge or even the machined face of the block puller. The object being that the drive shaft will eventually mate up squarely to the axle drive flange. Now tie the shaft safely to one side.
Undo and remove the nine oil seal housing nuts and spring washers.
Untab the drive flange nut lock tab with a small chisel. Attached the two misc bolts and nuts as clearly shown in Fig 11, and using the lever and socket undo and remove the flange nut. If it is intended to use the puller to extract the pinion housing, so that bearings can be changed, or a visual check is to be made on the pinion, then just loosen the flange nut three turns and do not remove it. Remove the old lock tab and bolt up the block puller to the face of the drive flange, make sure the centre screw is retracted enough to allow the puller face to be in full contact with axle flange. Tighten up the puller screw very tight and strike the puller end with a large hammer, if necessary retightening the puller screw. If the flange nut has been left in place keep good observation to ensure the puller pressure is immediately released when the taper releases.
Remove the puller, drive flange and oil seal housing. Note the seal housing hole at the 11 O’clock position is drilled out of pitch so that the housing can only be replaced in one position. Also note that the oil drain slot notched into the internal raised flange of the seal housing is positioned at the bottom.
If the axle is pre-1954 it is likely that it may be fitted with a triple type pinion bearing. The easiest way for the casual mechanic to check the bearing type is to refer to the view in Fig 13 to see if the unit is fitted with an oil thrower as shown here. If the oil thrower exists the unit has taper bearings, if not it is fitted with the old triple type bearing. For example all Bentley MKVI axles would originally have been fitted with triple bearings. The point that is important here is that in this triple bearing arrangement there is a hardened bearing pre-load spacer trapped between the oil seal housing and the outer track of the bearing. This spacer is apt to rotate and wear the oil seal housing, if this has happened the seal housing needs machining square and a thicker spacer fitting. This will entail setting the bearing pre-load by selecting a spacer that when clamped with the oil seal housing in position and nuts nipped up leaves a 0.003 inch clearance between the oil seal housing and pinion bearing housing. It is important at this stage to carry out such work and/or renew the bearing. On the other hand providing the axle is good it is possible to convert the pinion arrangement to taper bearings. In my own particular daily job of overhauling these axles on no account whatever do I refit triple bearing arrangement to any axle and all overhauled axles are automatically converted to taper bearings.
The next job is to machine the seal housing and fit a new seal. Check the woodruff keys and key way grooves for wear as shown at ‘C’ Fig 12. Worn grooves and keys can and do eventually scrap a pinion, or at the very least cause the pinion to be removed and remachined. The moral is, if the parts are worn replace them correctly now. Machine the drive flange sealing face as shown in Fig 6 and machine until absolutely true the flange face at ‘A’ in Fig 14 and machine groove ‘B’ as detailed.
Clean the face of the pinion housing, it will probably look like the outer face of the axle as in Fig 13, but in fact that is the pinion housing face, not the axle face. Clean the seal housing face and after ensuring a new oil seal is fitted, push the newly machined drive flange into position in the seal as in Fig 15. Set the key ways in the flange directly top and bottom and ensure the oil seal housing drain slot is at the bottom. Refer to Fig 16 and smear sealer half way up and in the top of each key way from the axle side only, as shown. Apply sealer lightly to the oil seal housing face, position the axle pinion so that the keys are as show in Fig 13 and then engage the drive flange key ways and the oil seal housing simultaneously on the pinion and nine studs. Refit the nine washers and nuts and cross tighten evenly. Fit two studs and nuts to two of the flange holes, and the assembly should then look like Fig 17. Note how the key way sealer has now been driven up the key ways without encroaching on the pinion taper interface.
DO NOT fit the lock tab at this stage. Once the parts are located, oil the face of the nut and screw it into position on the pinion. Tighten the nut to approx 125 lbs ft using the method shown in Fig 11. Once the flange is tight loosen the nut, remove it and fit the lock tab. Oil the nut face again, refit it and tighten to at least 140 ft. lb. Ensure the edges of the socket do not foul the lock tab and keep checking to ensure the tab does not turn and rip the tang. Pull the lock tab over the nut see Fig 18 . The method described above should ensure that the tab washer tang is not ripped when the nut is initially tightened.
Refit the propeller shaft and align the previously inscribed mating marks, make sure that the propeller mating flange locates absolutely central and flush with the axle flange. Cross tighten all the nuts evenly and check and refill the axle with 80 EP Oil.
