July 2014
Rolls-Royce Small Horsepower cars
25/30
Hub, Brake Drum and Wheel Bearings
These notes have been compiled while carrying out the work on a 1937 Rolls-Royce 25/30 Touring Saloon by Thrupp & Maberly. Chassis GRP29. Image
wheel-bearings-01
Brakes
The braking system on all pre-war Rolls-Royce cars is wholly mechanical. After the introduction of the Servo system the Rear brakes are operated both from the foot pedal AND the servo. The Front brakes are applied by the servo ALONE, which only acts when the car is in motion, and thus it is not practical to test the brakes for an MOT on a Rolls-Royce of this period on ‘rolling road’ test equipment.
A separate set of shoes within the rear brake drums is provided for the Handbrake.
Hub Removal
The removal of the hubs not only enables an inspection of the bearings, brake shoes, linings and surface of the drums but also access to clean and lubricate the adjacent brake actuating and adjusting levers and pivots.
The procedure is straight forward but does require some special tools. Do not be tempted to use cold chisels on the delicate parts which are easily damaged. Images
wheel-bearings-02, wheel-bearings-03 & wheel-bearings-04
Pay strict attention to the direction of threads of the parts. Some are marked with ON and OFF with a directional arrow and others with simple RH or LH.
If possible work on wheel at a time but, if not, ensure that parts are kept apart in separate sets since they are not necessarily interchangeable.
To inspect the condition of the brakes the hubs should be removed by the following procedures:
1. Front and Rear wheels Image wheel-bearings-05
1.1 Jack up the car and support securely on axle stands.
1.2 Remove the Dunlop wheels in accordance with the procedure in the Handbook.
1.3 Depress the ‘top hat’ Grease Cap (with R-R logo). This is best done with a special tool, but can be done without if care is taken. Image wheel-bearings-06
1.4Prise out the Spring Retaining Ring by means of a screwdriver inserted in one of the two slots in the hub. Note: Take care when releasing the helical spring behind.
1.5Remove the chrome plated Sliding Barrel
1.6Prise out the inner split spring steel wire Locking Ring from inside the grease cap retaining nut
1.7Remove the Grease Cap Retaining Nut, using a special tool. (Look for RH or LH to determine whether Right or Left hand thread )
Image wheel-bearings-07
1.8Remove the Grease Cap.
The front and rear hub procedures differ from here onward.
2. Front wheel hubs and brake drums Image 038 (editor to crop)
2.1 Remove the split pin from the castellated stub axle nut
2.2 Undo and remove the nut with the appropriate socket spanner (7/8 BSF, ¾ BSW). A long bar may be needed to provide sufficient torque.
Notes: 1. The threads are Left hand on Near side and Right hand on Off side.
2. Unlike the rear hub, this hexagon nut retains the whole drum and bearing assembly and thus on refitting must be really tight. It clamps the inner races of the two bearings against the brass collar.
2.3 Apply the hub puller and withdraw the hub.
2.4 Inspect the brake adjusting wing-nut and its actuating lever behind the backplate and ensure it is clean, has free movement and is lubricated. Images DSC05815 and 5816
See section 8.0 for more details. Images wheel-bearings-08 & wheel-bearings-09
3. Rear Wheel Hubs and Brake Drums Image 039 (editor to crop)
The rear axle is of the ‘fully floating’ type. The hubs are mounted on extensions of the axle tubes and the full driving torque is taken from the axle by the ‘Driving Dogs’. All weight is borne on the axle tube through the inboard and outboard angular contact ball bearings.
Note: Left hand threads are used on the Near side hubs, apart from the central axle shaft nut. The components concerned are marked ‘On’ and ‘Off’ with appropriate direction arrows.
3.1Back off foot brake adjustment as far as it will go by turning the wing nut behind brake drum.
3.2Release hand brake
3.3Withdraw pin from handbrake linkage (behind brake drum) having ` removed split pin and collar from behind.
3.6Remove shouldered washer and plain washer behind.
3.7Screw 2 x ¼ BSF bolts or special puller into tapped holes in ‘driving dog’.
3.8Withdraw the Driving Dog Images wheel-bearings-12 & wheel-bearings-13
The half shaft is now unsupported within the hub housing Image wheel-bearings-14
3.9Remove 3 x 2BA nuts and spring washers holding Locking Plate to the Axle Tube Nut. Note: A 3/16 BSF socket can be used for this. Image wheel-bearings-15
3.10 Withdraw Locking Plate
3.11 Unscrew the Axle Tube Nut with the special spanner. Image wheel-bearings-16
Notes:- the thread is Right hand on the Off side and Left hand on the Near side
– If a correct hub puller is not available it is possible to contrive one as per images 005 and 006, which involves using a ‘dummy’ or spare wheel nut with a puller behind it.
3.12 Locate a hub puller behind a dummy wheel nut and screw onto axle
3.13 Tighten hexagon nut in centre of puller to draw off the hub, complete with brake drum and bearings. Images wheel-bearings-17 & wheel-bearings-18
3.14 The removal of the hub assembly reveals the Collar Nut (part name ?) on the stub axle with its seating for the felt grease seal which rotates with the hub. This Nut, with serrated flange, need not be removed unless work is to done on the brake shoes. However, it is good practice to remove, clean and replace it. Its removal also provides some access to clean the chamber between the brake shoes. The Nut is secured with a locking plate which can be orientated in one of two positions and held by two slot headed screws. A special tool with serrations to match is recommended for undoing and replacing the Nut.
The near side is left hand threaded and the off side right hand.
Images wheel-bearings-19 & wheel-bearings-20
It need not be excessively tight but must firmly butt up to the steel plate in the brake assembly behind. The protruding end of this collar also acts as a stop when tightening up the hub bearing assembly. See below for details.
Image wheel-bearings-21
4. Bearing Removal
4.1 Remove the locking tab and unscrew the Bearing Retaining Nut of the inboard race, which can then be knocked out. Images wheel-bearings-22 & wheel-bearings-23
4.2 Remove the distance piece between the bearings and knock out the outboard bearing.
Note: The retaining nut thread is Right hand on the Off side and Left hand on the Near side.
All of the wheel bearings on a 25/30 are single row angular contact ball bearings and are of standard metric sizes and thus are very economical to replace. The original manufacturer was Messrs Hoffmann, later Ransome Hoffmann Pollard (RHP), of Chelmsford who have long since ceased manufacturing. Replacement bearings should be sourced from first class firms such as SKF or FAG. They generally supply bearings which are sealed ‘for life’. The seals can be removed or left in situ if you wish.
The SKF bearing sizes are as follows;
Rear wheel hub – Outboard – 6209-2RS1
– Inboard – 6210-2RS1
Front wheel hub- ?? (not changed on this occasion)
5 Rear Hub Bearing replacement
Having cleaned all parts, steps can be taken to reassemble and replace the assembly. If sealed bearings are used it becomes a comparatively clean job to carry out.
Image wheel-bearings-24
5.1Stand the hub on its end on a wooden or cardboard surface with the drum uppermost. Lightly grease or oil the inner casing.
Note: The hub is machined from a comparatively soft steel and the end is easily damaged if mishandled or placed unprotected on a hard surface.
5.2 Insert the outboard (smaller) bearing and gently lower into position. With a soft aluminium, or similar, drift tap around the outer race until it seats on the ledge.
5.3 Insert the tubular distance piece (spacer) with the flange uppermost.
5.4 Insert the inboard (larger) bearing which needs to be a snug fit so that there is no risk of the outer race rotating in its housing.
Note: If there is any doubt, a mild Loctite can be used around the housing and allowed to set in warm conditions.
5.5 The large Bearing Retaining Nut with its serrated periphery, complete with its hard composition washer should now be screwed down very tightly to firmly grip the outer race of the bearing. (Right hand thread on Off-side and Left hand on the Near-side).
Image wheel-bearings-25
5.6 Lock it into position with the tab which is retained by a small square headed 2BA bolt, spring washer and nut.
Notes: The inner races of both inboard and outboard bearings are clamped firmly to the rotating assembly by the Axle Tube Nut and distance piece.
The inboard bearing Outer race is clamped by the Bearing Retaining Nut with its composition washer and must not rotate within its housing.
The outer race of the outboard bearing is the ‘floating’ one which can move axially in service.
6. Rear Hub Reinstallation
The hub is now ready for installation. Note: I warmed my hubs for an hour or two on the Aga to expand the clearances and ease its introduction onto the cold axle shaft.
6.1 Clean the axle shaft and lightly oil or grease.
6.2 Offer the hub assembly and slide partly on.
If sealed bearings are used, squirt some oil (engine/gearbox type) into the distance piece area and ensure some goes into the housing below. This will distribute itself in operation and protect against later corrosion.
6.3 Push the hub assembly, rotating to help move it, fully up to the drum backplate.
6.4 Introduce the ‘axle tube nut’ (a ring having three studs and three holes)
6.5 Tighten with the special tool with a 15 to 18 inch Tommy bar. (Off side Right hand and Near side Left hand threads). This is the only nut on the rear axle which needs to be really tight .
Hint: In order to apply sufficient torque, the drum needs to be secure. Place an axle stand below the drum and gently lower the jack so that the drum rests on the stand and thus prevents it turning during the tightening process.
The axle tube nut must clamp the two bearing inner races and the distance piece into a ‘rock-solid’ assembly against the end of the collar nut incorporating the inner race for the felt seal. It is the outer race of the outer (smaller) bearing which is the only one which ‘floats’ in its housing.
6.6 When it is firmly in place fit the ‘locking plate’. (This ring has more than one possible orientation to help locate the best positioned tabs)
6.7 Fix the three 2 BA retaining nuts and spring washers (preferably new ones) onto the studs.
Note: The 5/8 BSW castellated axle shaft nut only holds the Driving Dog in place and thus does not require excessive tightening. Tighten to an easily accessible split pin hole.
6.8 Grease all parts with a general purpose grease.
The final step is to reinstall the ‘top hat’ grease cap, the sliding barrel and the wheel nuts.
6.9 Insert the Grease Cap and then the circular Grease Cap Retaining Nut. LH or RH will be stamped on it to indicate direction for tightening.
Note: On my car the Front Off side hub was fitted with a Left hand nut which suggests that the hubs have been accidentally interchanged at some time in the past?
There are a series of holes around the perimeter of both the Nut and the Hub into which it is screwed. Tighten until one pair nearly coincide and then nip up to align.
6.10 The Wire Locking Ring can then be inserted with its tail locating through the holes to act as a locking device.
6.11 Now the coil spring can be inserted.
6.12 The chromium plated Sliding Barrel is placed over it and pressed into the hub so that the stubs coincide with indents within the hub.
Notes: It needs to be pressed in very hard to enable the split spring retaining ring to be sprung into the groove within the end of the hub.
Without a special compression tool this is a two man job.
7. Brake Drums
The massive finned iron brake drums provide exceptional braking effect for the period, if kept in good order. The handbrake shoes act on the inner section of the drums, separately from the footbrake.
When the hubs have been removed give the drums a good clean and ensure the two rows of small diameter drain holes are clear. These drain any ingress of oil from the differential which may flow to the hub as a result of the car leaning at an acute angle.
If the braking surfaces inside the drum do not need regrinding it is good practice to roughen them with emery to a cross-hatch pattern and clean thoroughly with a solvent.
Image wheel-bearings-26
8.Brake Shoes
If the linings are in good condition it is best not to disturb them unnecessarily. If the linings are asbestos and you wish to clean them and roughen with emery, then use a breathing mask and a vacuum cleaner which has a disposable paper collecting liner.
Images wheel-bearings-27 & wheel-bearings-28
9.0 Brake adjusting linkages (front)
Some of the pivot points on the front actuating and adjusting system are not lubricated by the central system and can become seized after many years, especially if not regularly used and oiled. It is then impossible to adjust the brakes with the turnbuckle wing-nut which should turn by finger pressure alone.
In my car, the front offside linkages were free but the near side seriously seized.
Undo the two clamping screws, 3/16 BSF, on the inside boss which is located by a key.
Remove the leather boot from the top of the vertical rod and separate the ball joint at end of lever from the rod.
If unseized it should be possible to slide the assembly of levers and adjusting mechanism off the stub shaft.
In my case the components were seriously seized and only freed by heating the boss to redheat by a methylacetylene-propadiene (MAPPS) torch to expand it sufficiently to drive it off the stub shaft.
After removal the parts were cleaned and mating surfaces treated with fine (400) emery paper before greasing and re-assembly.
Tip: Use a grease containing molybdenum disulphide which will continue to lubricate even when the grease itself has dried out.
Image wheel-bearings-29
The leather boots at top and bottom of each vertical rod were removed, ball joints cleaned and re-assembled with fresh grease. Image wheel-bearings-30
9. Chromium Plating
While the wheel hubs were off the car I took the opportunity to have the centre components rechromed i.e. the Wheel Nuts, Sliding Barrels and Grease caps. The improvement in the car’s appearance is marked.
Images wheel-bearings-31 & wheel-bearings-32
References:
Rolls-Royce Service Instruction Leaflet RR/V1 of 7th January 1945
RROC Flying Lady – pp 472/3 October 1960
1232January 1970
Spectre – journal of the Phantom III Technical Society, issue 14- 1975
Acknowledgements
The writer wishes to acknowledge the invaluable help and advice from Messrs John Hibbert and Stephen Wragg, fellow owners of 25hp cars, without whom the task could not have been undertaken.
These notes have been compiled in good faith by Bryan McGee. They have been drawn from various sources and I make no claim to be an authority on the matter. They carry no official endorsement by the Club and are offered freely for reference by members to use at their own risk
