The attached document provides Workshop Hints for small horsepower Rolls-Royce cars – Rolls-Royce 25/30 – kindly provided by Bryan McGee. This particular document focuses on Brake servo.
Last updated: April 2013
Workshop Hints April 2013
Rolls-Royce 25/30 chassis no: GRP29 Image references shown in blue
Headline image; GRP 29 at Chatsworth Country Fair, September 2012
Photograph by Sally Botham Estates
Background
The celebrated Rolls-Royce gearbox-driven servo assisted four-wheel braking system was introduced in the 1920s for the large ‘New Phantom’ model, destined to replace the Silver Ghost, and was soon thereafter introduced on the ‘small horsepower’ 20hp in 1925. This Servo design continued to be used in various forms on all Rolls-Royce and Bentley chassis type models for over 40 years until 1976 when it was superceded on the final series of the Phantom VI. It was not used on the monocoque Silver Shadow in 1965 and its successors.
In this paper we will consider the wholly mechanical version as used in the later ‘small horsepower’ models of the 1930s. The overhaul, rebuilding and adjustment of the servo does not require specialised tools and can be carried out by any owner who has some mechanical aptitude.
The initial design of the servo system was carried out by A. J. Rowledge, a young engineer who was ex Napiers, and whom Rolls-Royce sent to France in 1923 to study the four-wheel braking systems then being used by Perrot, Hispano-Suiza and Renault. Although the servo probably owes most to Hispano-Suiza which itself was derived from Renault, the Rolls-Royce system differs from their design which used a drum rather than a disc type brake. The more complex Rolls-Royce lever arrangement also has the advantage of working equally well in both forward and reverse directions.
Diagram of Rolls-Royce Four-Wheel Brake System Fig. brake-servo-01.jpg
The servo system is driven via a worm gear from the output shaft of the gearbox to provide braking assistance which is directly proportional to the speed of the car. This assistance supplements the driver’s efforts in applying the rear brakes and provides the only braking effort for the front brakes. It is said by some that it therefore provides an anticipation of modern traction control. i.e. If the rear brakes should lock up during a skid, the servo stalls and automatically releases the front brakes to restore full steering control to the driver. It only reapplies front wheel braking once traction is restored.
Note: This theory is somewhat refuted by correspondence in RREC Bulletin 149 of March/April 1985.
The servo is equally effective in forward or rearward motion. There is however a degree of ‘servo lag’ when the car is moving very slowly such as when trickling in slow traffic.
Operation and maintenance
See: Handbook Fig. ‘The Servo Motor and its Connections’ Fig. brake-servo-02.jpg
Although the system looks inordinately complex on first examination, it has proved robust and reliable in operation over many years, provided the linkages and pivots are kept well lubricated. The Servo drum rotates whenever the rear wheels are turning, anticlockwise when in forward drive and clockwise when in reverse. The Coupling Rods are labelled accordingly ‘F’ and ‘R’.
Applying the footbrake forces A1 and A2 apart which brings the friction linings in the driven plates in contact with a rotating disc within the drum in an action not unlike a disk brake. ‘R’ or ‘F’ is raised according to the direction in which the plate revolves. In both cases the arm of lever ‘T’ is lifted, applying front brakes through link ‘Tf’ and assisting rear brakes through rod ‘Tr’.
See Figures 1 to 5 in brake-servo-03.jpg
This may be better understood by looking at Fig.1 and Fig.4 in this set. Light pressure on the brake pedal pulls link ‘1’ and rotates lever 2 (A1) taking lever 4 (A2) with it. This directly applies rear brakes via equaliser ’6’.
Note: The Equaliser resembles a bevel gear differential. ( see Fig. 5)
Further pressure rotates levers 23 or 26 and raises 16 (T) applying the front brakes via 15 ( Tf).
The split boss of the lever T1 is clamped to the cross shaft by a friction lining, through spring Ts, which provides damping of any violent application of the front brakes. A pneumatic damping device Td was introduced on later models to eliminate noise from the servo levers when the brakes are released.
Eventually the servo friction linings need replacement and that provides an opportunity to strip and clean the servo system, replace the friction linings, roughen the steel contact faces and lubricate where necessary.
In all 25/30 cars the friction linings are ‘floating’ and are thus not attached to the driving or driven members.
Procedure
Refer to the Chapter in the Handbook ‘Care and Adjustment of the Four-Wheel Brakes’
In which there is the illustration mentioned above with relevant references.
N.B. Make sure that you are meticulous to mark the orientation and order for each part removed since correct reassembly can be very dependent upon this procedure.
Damper dashpot in two views Figs. brake-servo-04.jpg & brake-servo-05.jpg
NB. Count the turns and note so that it can later be reassembled in same position.
NB. Note differences. ‘R’ has an eye at the base. ‘F’ a slotted fork
Reassemble these before ‘Tf’.
Note: The bolts have heads which are assymetrical and thus they need to be carefully orientated on reassembly.
NB. DO NOT withdraw Driving plate which backs onto gearbox. Its shaft can drop a distance piece into the gearbox if withdrawn more than, say, ½ inch. It is suggested that a wire through one of the peripheral holes can be tied to a suitable fixture to hold the driving plate in position during this and subsequent operations.
Cross-shaft, part exposed Fig. brake-servo-06.jpg
The ‘T1’ assembly can now be separated and cleaned before putting to one side.
The servo assembly can also benefit from a cursory clean before disassembly.
Servo Driving Plate and Cross-shaft Fig. brake-servo-08.jpg
Disassembly of Servo
The Servo assembly comprises a series of components mounted along two concentric shafts where the spacing and orientation of each item is important. It is helpful to mark one side of each component with Tippex, or similar and to carry out the disassembly over a large container, such as a seed tray, that would retain any parts which are dropped etc.
In order to maintain the order for ease of reassembly it is recommended that a length of stiff wire is used to hold the parts removed. A right angle bend at the end of the wire will prevent loss of the parts. Alternatively the parts can be laid out in order on an uncluttered table.
Complete set of servo shaft components Fig: brake-servo-09.jpg
Close-up of inboard components brake-servo-10.jpg
Close-up of mid components brake-servo-11.jpg
Close-up of outboard components brake-servo-12.jpg
Procedure:
1.Remove circlip at end of shaft and carefully save.
2.Unscrew the large retaining nut which has serrations on its inside face
3.Pull off serrated washer
4.Remove buffer springs and keep them in correct order. They have internal tabs which engage with slots in the shaft.
5.A spacer washer is located between the pairs of springs
6.Slide off the washer/ball race
7.followed by the first ball cage complete with its captive balls
8.Remove the cam levers A1 and A2 as a pair.
9.Separate the two levers with great care to save the four uncaged balls located between them.
10.Next remove the second ball cage with its captive balls.
11.This is followed by a castellated ring nut with a ball race machined in its outer face.
12.A tab washer behind it needs to be bent back before the nut can be rotated.
13.A spacer washer sits behind the tab washer
14.The Bridge Support Plate on my 25/30 is sandwiched between the housings of a lovely Hoffman ball bearing. (Note: On some other models this bearing is a simple bronze bush).
If it has a ball bearing then it may be necessary to file the peened ends of the four 3/16’’ BSF bolts clamping the housings, to allow them to be undone and the bearing removed.
15.This finally leaves the two lever arms ‘R’ and ‘F’ to be removed complete with their bronze bushes.
16.The Servo itself can now be separated to reveal the friction linings and faces.
Two views of friction components separated Figs. brake-servo-13.jpg & brake-servo-14.jpg
Friction Linings
On 20hp, 20/25 up to chassis GBJ1 and Bentley 3-1/2 up to chassis B-2-DG the linings are stapled to the drive plates. On all cars thereafter the linings are ‘free floating’.
Note: The early style stapled lining types are easily converted to accept free floating linings by filling the staple holes in the inner and outer drive plates with solder or epoxy filler.
It is likely that the two Ferodo type friction linings and their four faces will have become glazed or oil contaminated by use. Before replacing the friction linings with new components the steel faces on which they bear must be refinished with a fine emery, scotchbrite or similar, to restore an appropriate level of roughness. Alternatively valve grinding paste can be used with the old linings as a carrier to roughen the surfaces. Meticulous cleaning afterwards will then be necessary.
Servo unit friction components Fig. brake-servo-15.jpg
Replacement linings are available from the usual sources and the dimensions will need to be checked to ensure they are a snug but free rotational fit in the recesses and that they have a degree of ‘float’. Any excess on the OD can be removed on a lathe or a file.
Note: Although the modern replacement linings are now asbestos free, it is suggested that a mask be worn when working with friction materials.
Bearings
The three ball bearings, one a complete unit and the two cages and balls, will benefit from thorough cleaning with a solvent and, if possible treatment by immersion in a degreaser, such as Jizer, followed by brake & clutch cleaning fluid in an ultrasonic bath to remove all traces of contamination. The bearings should then be dried and spun with some engine oil before packing with grease prior to reassembly in the system.
Reinstallation
The rebuild of the system must be carried out very systematically to avoid having to repeat tasks unnecessarily. For example, the two long ¼ BSF bolts holding the dashpot damper Td must be inserted with their square heads on the gearbox side before fixing the strut bracket and offering up the main assemblies. They cannot be inserted later.
Now look at the numbered references in Figs 1 to 4 which are for guidance only since the 25/30 design differs from this diagram in small ways. Fig. ServoFigs.jpg
1.Place the new friction linings into their recesses in the inboard and outboard servo discs and reassemble the discs together with the friction plate and the helical rebound spring.
2.Ensure that the three pins fixed to the outboard driving plate move freely in the bushes in the inner driven plate. A light smear of wheel bearing grease on the pins will ensure a long service life. (21)
Note: It is suggested that you clamp this disc subassembly together with a C-clamp to overcome the helical spring pressure until the servo has been fully built up.
3.Orientate the sub-assembly so that the tab on the edge of the outer drive plate is in the ‘six ‘o clock’ position and the two stops protruding from this plate, one long and one short, are on the lower side. (22) and (25).
4.Mount the two arms, for forward and rearward motion, on their lightly greased flanged bronze bushes and push up to the outboard disc. Check that they can rotate freely up to their respective stops. (23) and (26)
5.Slide on the inboard bearing housing and its spacer washer followed by the transverse Bridge Support Plate.
Note: The Support Plate is not symmetrical about its horizontal centre line and must be correctly orientated.
6.Warm the ball bearing prior to sliding it onto the shaft. ( I used our Aga for this)
7.Grease the bearing thoroughly and place the outboard bearing housing in position and refit the four 3/16 BSF bolts with square heads inboard.
Note: The threads of the bolts and nuts should be thoroughly cleaned and Loctite used to secure them.
8.Fit the spacer washer followed by a tab washer.
9.Tighten the inner bearing race firmly in position by means of the castellated nut which bears on the spacer washer to do this. This nut also incorporates the inboard race for the first ball cage.
10.Lock the castellated nut in position with the tabs.
11.Introduce the first of the two free thrust ball cages, after greasing. (32)
12.Preassemble the two cam levers, ‘A1’ and ‘A2’ by greasing A1 and positioning a steel ball at foot of each cam incline and offer up A2. (2) and (4)
Notes: 1. Levers can engage in one of four positions. The sole correct mating is with the levers staggered by 3/8 “ with A1 forward and A2 trailing.
2. Replacement steel balls, if required, are obtainable from motorcycle repair shops.
13.Introduce the second thrust ball cage followed by its outboard race after greasing
14.Slide on the two pairs of springs which are back to back and separated by a washer.
15.A serrated washer butts up to the springs and, finally
16.A hexagonal nut with serrated inner face is rotated to compress the assembly of components and allows the C-clamp to be removed
17.A circlip is provided to fit onto the most outboard threads on the shaft.
Note: The degree of clamping by tightening the hexagon will be carried out later in accordance with the instructions in the Handbook for Adjustment of the Servo.
The whole assembly is now ready.
1.The Suspension link T1, which has a friction lined and split boss, needs to be loosely positioned with a wire around the unclamped boss to hold it together.
Suspension link and ‘T’ levers Fig. brake-servo-17.jpg
Note: The cross shaft should be lubricated with engine oil prior to assembly. Thereafter it will be oiled by the chassis lubrication system
2.The Servo assembly and T1 need to be juggled until the large aperture of the Bridge Support Plate can be slid over the Cross Shaft, the small aperture over the stud into the Strut bracket and the spigot on the Servo enters the recess in the Driving Plate. Push assembly up to the Driving plate.
3.Insert flanged tube over the stud and into the bracket. Loosely tighten 5/8 BSF nut.
Note: It is now safe to remove the wire holding the Driving plate in position.
4.A spacer followed by a tab washer can now be added to the Cross shaft
5.Add the 1-1/8 BSF nut and tighten up to the Suspension link T1.
6.Reposition the key and slide the lever into approximate position.
7.Position the lever axially ( a mirror beneath may be needed).
8.Replace the clamping bolt with square head at the lower right and the ¼ BSF (?) hexagon nut at upper left.
9.The clamping bolt and spring, Ts, can now be fitted to apply a clamping force by the boss of T1 onto the cross shaft. Tighten the nut below the spring until the assembly feels solid, then untighten the nut by one full turn.
10.Refit the damper Td by the two ¼ “BSF nuts and reconnect the chassis lubrication tube.
Note: The damper is designed to damp only when the rod is pulled out. Check to ensure the piston does not stick. A faulty damper may be the result of a missing or stuck 1/8 “ steel ball located under the large brass screw.
The various levers and links of the system can now be recoupled by insertion of their clevis pins, which should be lightly greased and held in position with their retention caps by new split pins.
Note: On no account should the lengths of any these levers or links be altered. They are factory set and should need no adjustment.
Rebuilt system ready for trial Fig. brake-servo-16.jpg
Adjustment of the Servo.
Instructions for adjustment are given in the Handbook for the car and, it is claimed that once they have been set, they should run for 20,000 miles without further attention.
The RROC notes recommend a further check, while the floor boards are still up and at least one rear wheel is jacked up, starting the engine, engaging top gear and running at an indicated 10 mph.
Depress the brake pedal until levers A1 and A2 start to engage levers Tf for the front brakes and lever Tr for the rear. Pedal travel to start rotation of A2 should be no less than ½ inch, measured at the top of the pedal. Further depression should start to apply the rear brakes and induce stalling of the engine.
Testing of Braking System
Due to its configuration the Rolls-Royce system cannot be tested for braking efficiency by an M.O.T. type ‘rolling road’. It is therefore recommended that a Ferodo Tapley Meter is clamped to the running board to measure the efficiency whilst on the road.
Ferodo Tapley Meter Fig. brake-servo-18.jpg
Bryan McGee
2013
BIBLIOGRAPHY and ACKNOWLEDGEMENTS
Handbook of the 25 – 30 HP Rolls – Royce Car
Number XVII by Rolls-Royce Motors
Service Instructions for Rolls-Royce Cars (TSD publication 2066), Chapter ‘J’ Brakes by Rolls-Royce Motors
Rolls-Royce Small Horsepower Brake Systems by R. Haynes, published by RREC 1983
RREC Bulletins:
No. 6, pp 2–3 The Rolls–Royce Mechanical Servo by Nigel H. Hughes
No. 31 , pp 11-12. Adjustment of Servo Motors – All Models by R. Haynes
No. 96, pp 14-18. Overhauling your Servo by R. E. Kirby
No. 119, pp14-15, Servo Overhaul – late 20hp chassis GVO74 by Nick Jago
No. 149, pp 55-56, Servo Braking by Donald Bastow (correspondence)
No. 149, p 56, Brakes – Yet again by D. Stewart Watson (correspondence)
No. 149, p 56, Servo Operation by G. Ashley-Carter (correspondence)
RREC Technical Manuals:
1972, pp 172,173,170-171.
1978, pp 70-76.
RROC Flying Lady:
September 1969, pp 1198-1200, Servo Brake System- How it Works by Richard C. Hitchcock
November 1969, pp 1212-1215, Servo Adjustment and Overhaul Pre-War Cars by
R. E. Kirby with notes by R. Haynes.
January 2000, pp 5934- 5939, The R-R Servo on Small HP Cars by Gil Fuqua
The Hyphen in Rolls-Royce – The Story of Claude Johnson by Wilton .J Oldham
Once again I cannot speak highly enough for the advice and encouragement I received from John Hibbert, Stephen Wragg and Matthew Pickles, local experts in the marque.
Workshop Hints April 2013
Rolls-Royce Brake Servo
Rolls-Royce 25/30 chassis no: GRP29 Image references shown in blue
Headline image; GRP 29 at Chatsworth Country Fair, September 2012
Photograph by Sally Botham Estates
Background
The celebrated Rolls-Royce gearbox-driven servo assisted four-wheel braking system was introduced in the 1920s for the large ‘New Phantom’ model, destined to replace the Silver Ghost, and was soon thereafter introduced on the ‘small horsepower’ 20hp in 1925. This Servo design continued to be used in various forms on all Rolls-Royce and Bentley chassis type models for over 40 years until 1976 when it was superceded on the final series of the Phantom VI. It was not used on the monocoque Silver Shadow in 1965 and its successors.
In this paper we will consider the wholly mechanical version as used in the later ‘small horsepower’ models of the 1930s. The overhaul, rebuilding and adjustment of the servo does not require specialised tools and can be carried out by any owner who has some mechanical aptitude.
The initial design of the servo system was carried out by A. J. Rowledge, a young engineer who was ex Napiers, and whom Rolls-Royce sent to France in 1923 to study the four-wheel braking systems then being used by Perrot, Hispano-Suiza and Renault. Although the servo probably owes most to Hispano-Suiza which itself was derived from Renault, the Rolls-Royce system differs from their design which used a drum rather than a disc type brake. The more complex Rolls-Royce lever arrangement also has the advantage of working equally well in both forward and reverse directions.
Diagram of Rolls-Royce Four-Wheel Brake System Fig. RRbrakes.jpg
The servo system is driven via a worm gear from the output shaft of the gearbox to provide braking assistance which is directly proportional to the speed of the car. This assistance supplements the driver’s efforts in applying the rear brakes and provides the only braking effort for the front brakes. It is said by some that it therefore provides an anticipation of modern traction control. i.e. If the rear brakes should lock up during a skid, the servo stalls and automatically releases the front brakes to restore full steering control to the driver. It only reapplies front wheel braking once traction is restored.
Note: This theory is somewhat refuted by correspondence in RREC Bulletin 149 of March/April 1985.
The servo is equally effective in forward or rearward motion. There is however a degree of ‘servo lag’ when the car is moving very slowly such as when trickling in slow traffic.
Operation and maintenance
See: Handbook Fig. ‘The Servo Motor and its Connections’ Fig. RRservo.jpg
Although the system looks inordinately complex on first examination, it has proved robust and reliable in operation over many years, provided the linkages and pivots are kept well lubricated. The Servo drum rotates whenever the rear wheels are turning, anticlockwise when in forward drive and clockwise when in reverse. The Coupling Rods are labelled accordingly ‘F’ and ‘R’.
Applying the footbrake forces A1 and A2 apart which brings the friction linings in the driven plates in contact with a rotating disc within the drum in an action not unlike a disk brake. ‘R’ or ‘F’ is raised according to the direction in which the plate revolves. In both cases the arm of lever ‘T’ is lifted, applying front brakes through link ‘Tf’ and assisting rear brakes through rod ‘Tr’.
See Figures 1 to 5 in ‘ServoFigs.jpg’
This may be better understood by looking at Fig.1 and Fig.4 in this set. Light pressure on the brake pedal pulls link ‘1’ and rotates lever 2 (A1) taking lever 4 (A2) with it. This directly applies rear brakes via equaliser ’6’.
Note: The Equaliser resembles a bevel gear differential. ( see Fig. 5)
Further pressure rotates levers 23 or 26 and raises 16 (T) applying the front brakes via 15 ( Tf).
The split boss of the lever T1 is clamped to the cross shaft by a friction lining, through spring Ts, which provides damping of any violent application of the front brakes. A pneumatic damping device Td was introduced on later models to eliminate noise from the servo levers when the brakes are released.
Eventually the servo friction linings need replacement and that provides an opportunity to strip and clean the servo system, replace the friction linings, roughen the steel contact faces and lubricate where necessary.
In all 25/30 cars the friction linings are ‘floating’ and are thus not attached to the driving or driven members.
Procedure
Refer to the Chapter in the Handbook ‘Care and Adjustment of the Four-Wheel Brakes’
In which there is the illustration mentioned above with relevant references.
N.B. Make sure that you are meticulous to mark the orientation and order for each part removed since correct reassembly can be very dependent upon this procedure.
Damper dashpot in two views Figs. DSC06626/7
NB. Count the turns and note so that it can later be reassembled in same position.
NB. Note differences. ‘R’ has an eye at the base. ‘F’ a slotted fork
Reassemble these before ‘Tf’.
Note: The bolts have heads which are assymetrical and thus they need to be carefully orientated on reassembly.
NB. DO NOT withdraw Driving plate which backs onto gearbox. Its shaft can drop a distance piece into the gearbox if withdrawn more than, say, ½ inch. It is suggested that a wire through one of the peripheral holes can be tied to a suitable fixture to hold the driving plate in position during this and subsequent operations.
Cross-shaft, part exposed Fig. DSC06608
The ‘T1’ assembly can now be separated and cleaned before putting to one side.
The servo assembly can also benefit from a cursory clean before disassembly.
Servo Driving Plate and Cross-shaft Fig. DSC06612
Disassembly of Servo
The Servo assembly comprises a series of components mounted along two concentric shafts where the spacing and orientation of each item is important. It is helpful to mark one side of each component with Tippex, or similar and to carry out the disassembly over a large container, such as a seed tray, that would retain any parts which are dropped etc.
In order to maintain the order for ease of reassembly it is recommended that a length of stiff wire is used to hold the parts removed. A right angle bend at the end of the wire will prevent loss of the parts. Alternatively the parts can be laid out in order on an uncluttered table.
Complete set of servo shaft components Figs: DSC06631
Close-up of inboard components 06632
Close-up of mid components 06633
Close-up of outboard components 06634
Procedure:
1.Remove circlip at end of shaft and carefully save.
2.Unscrew the large retaining nut which has serrations on its inside face
3.Pull off serrated washer
4.Remove buffer springs and keep them in correct order. They have internal tabs which engage with slots in the shaft.
5.A spacer washer is located between the pairs of springs
6.Slide off the washer/ball race
7.followed by the first ball cage complete with its captive balls
8.Remove the cam levers A1 and A2 as a pair.
9.Separate the two levers with great care to save the four uncaged balls located between them.
10.Next remove the second ball cage with its captive balls.
11.This is followed by a castellated ring nut with a ball race machined in its outer face.
12.A tab washer behind it needs to be bent back before the nut can be rotated.
13.A spacer washer sits behind the tab washer
14.The Bridge Support Plate on my 25/30 is sandwiched between the housings of a lovely Hoffman ball bearing. (Note: On some other models this bearing is a simple bronze bush).
If it has a ball bearing then it may be necessary to file the peened ends of the four 3/16’’ BSF bolts clamping the housings, to allow them to be undone and the bearing removed.
15.This finally leaves the two lever arms ‘R’ and ‘F’ to be removed complete with their bronze bushes.
16.The Servo itself can now be separated to reveal the friction linings and faces.
Two views of friction components separated Figs. DSC06620/1
Friction Linings
On 20hp, 20/25 up to chassis GBJ1 and Bentley 3-1/2 up to chassis B-2-DG the linings are stapled to the drive plates. On all cars thereafter the linings are ‘free floating’.
Note: The early style stapled lining types are easily converted to accept free floating linings by filling the staple holes in the inner and outer drive plates with solder or epoxy filler.
It is likely that the two Ferodo type friction linings and their four faces will have become glazed or oil contaminated by use. Before replacing the friction linings with new components the steel faces on which they bear must be refinished with a fine emery, scotchbrite or similar, to restore an appropriate level of roughness. Alternatively valve grinding paste can be used with the old linings as a carrier to roughen the surfaces. Meticulous cleaning afterwards will then be necessary.
Servo unit friction components Fig. DSC06623
Replacement linings are available from the usual sources and the dimensions will need to be checked to ensure they are a snug but free rotational fit in the recesses and that they have a degree of ‘float’. Any excess on the OD can be removed on a lathe or a file.
Note: Although the modern replacement linings are now asbestos free, it is suggested that a mask be worn when working with friction materials.
Bearings
The three ball bearings, one a complete unit and the two cages and balls, will benefit from thorough cleaning with a solvent and, if possible treatment by immersion in a degreaser, such as Jizer, followed by brake & clutch cleaning fluid in an ultrasonic bath to remove all traces of contamination. The bearings should then be dried and spun with some engine oil before packing with grease prior to reassembly in the system.
Reinstallation
The rebuild of the system must be carried out very systematically to avoid having to repeat tasks unnecessarily. For example, the two long ¼ BSF bolts holding the dashpot damper Td must be inserted with their square heads on the gearbox side before fixing the strut bracket and offering up the main assemblies. They cannot be inserted later.
Now look at the numbered references in Figs 1 to 4 which are for guidance only since the 25/30 design differs from this diagram in small ways. Fig. ServoFigs.jpg
1.Place the new friction linings into their recesses in the inboard and outboard servo discs and reassemble the discs together with the friction plate and the helical rebound spring.
2.Ensure that the three pins fixed to the outboard driving plate move freely in the bushes in the inner driven plate. A light smear of wheel bearing grease on the pins will ensure a long service life. (21)
Note: It is suggested that you clamp this disc subassembly together with a C-clamp to overcome the helical spring pressure until the servo has been fully built up.
3.Orientate the sub-assembly so that the tab on the edge of the outer drive plate is in the ‘six ‘o clock’ position and the two stops protruding from this plate, one long and one short, are on the lower side. (22) and (25).
4.Mount the two arms, for forward and rearward motion, on their lightly greased flanged bronze bushes and push up to the outboard disc. Check that they can rotate freely up to their respective stops. (23) and (26)
5.Slide on the inboard bearing housing and its spacer washer followed by the transverse Bridge Support Plate.
Note: The Support Plate is not symmetrical about its horizontal centre line and must be correctly orientated.
6.Warm the ball bearing prior to sliding it onto the shaft. ( I used our Aga for this)
7.Grease the bearing thoroughly and place the outboard bearing housing in position and refit the four 3/16 BSF bolts with square heads inboard.
Note: The threads of the bolts and nuts should be thoroughly cleaned and Loctite used to secure them.
8.Fit the spacer washer followed by a tab washer.
9.Tighten the inner bearing race firmly in position by means of the castellated nut which bears on the spacer washer to do this. This nut also incorporates the inboard race for the first ball cage.
10.Lock the castellated nut in position with the tabs.
11.Introduce the first of the two free thrust ball cages, after greasing. (32)
12.Preassemble the two cam levers, ‘A1’ and ‘A2’ by greasing A1 and positioning a steel ball at foot of each cam incline and offer up A2. (2) and (4)
Notes: 1. Levers can engage in one of four positions. The sole correct mating is with the levers staggered by 3/8 “ with A1 forward and A2 trailing.
2. Replacement steel balls, if required, are obtainable from motorcycle repair shops.
13.Introduce the second thrust ball cage followed by its outboard race after greasing
14.Slide on the two pairs of springs which are back to back and separated by a washer.
15.A serrated washer butts up to the springs and, finally
16.A hexagonal nut with serrated inner face is rotated to compress the assembly of components and allows the C-clamp to be removed
17.A circlip is provided to fit onto the most outboard threads on the shaft.
Note: The degree of clamping by tightening the hexagon will be carried out later in accordance with the instructions in the Handbook for Adjustment of the Servo.
The whole assembly is now ready.
1.The Suspension link T1, which has a friction lined and split boss, needs to be loosely positioned with a wire around the unclamped boss to hold it together.
Suspension link and ‘T’ levers Fig. DSC06618
Note: The cross shaft should be lubricated with engine oil prior to assembly. Thereafter it will be oiled by the chassis lubrication system
2.The Servo assembly and T1 need to be juggled until the large aperture of the Bridge Support Plate can be slid over the Cross Shaft, the small aperture over the stud into the Strut bracket and the spigot on the Servo enters the recess in the Driving Plate. Push assembly up to the Driving plate.
3.Insert flanged tube over the stud and into the bracket. Loosely tighten 5/8 BSF nut.
Note: It is now safe to remove the wire holding the Driving plate in position.
4.A spacer followed by a tab washer can now be added to the Cross shaft
5.Add the 1-1/8 BSF nut and tighten up to the Suspension link T1.
6.Reposition the key and slide the lever into approximate position.
7.Position the lever axially ( a mirror beneath may be needed).
8.Replace the clamping bolt with square head at the lower right and the ¼ BSF (?) hexagon nut at upper left.
9.The clamping bolt and spring, Ts, can now be fitted to apply a clamping force by the boss of T1 onto the cross shaft. Tighten the nut below the spring until the assembly feels solid, then untighten the nut by one full turn.
10.Refit the damper Td by the two ¼ “BSF nuts and reconnect the chassis lubrication tube.
Note: The damper is designed to damp only when the rod is pulled out. Check to ensure the piston does not stick. A faulty damper may be the result of a missing or stuck 1/8 “ steel ball located under the large brass screw.
The various levers and links of the system can now be recoupled by insertion of their clevis pins, which should be lightly greased and held in position with their retention caps by new split pins.
Note: On no account should the lengths of any these levers or links be altered. They are factory set and should need no adjustment.
Rebuilt system ready for trial Fig. DSC06641
Adjustment of the Servo.
Instructions for adjustment are given in the Handbook for the car and, it is claimed that once they have been set, they should run for 20,000 miles without further attention.
The RROC notes recommend a further check, while the floor boards are still up and at least one rear wheel is jacked up, starting the engine, engaging top gear and running at an indicated 10 mph.
Depress the brake pedal until levers A1 and A2 start to engage levers Tf for the front brakes and lever Tr for the rear. Pedal travel to start rotation of A2 should be no less than ½ inch, measured at the top of the pedal. Further depression should start to apply the rear brakes and induce stalling of the engine.
Testing of Braking System
Due to its configuration the Rolls-Royce system cannot be tested for braking efficiency by an M.O.T. type ‘rolling road’. It is therefore recommended that a Ferodo Tapley Meter is clamped to the running board to measure the efficiency whilst on the road.
Ferodo Tapley Meter Fig. DSC06644.jpg
Bryan McGee
2013
BIBLIOGRAPHY and ACKNOWLEDGEMENTS
Handbook of the 25 – 30 HP Rolls – Royce Car
Number XVII by Rolls-Royce Motors
Service Instructions for Rolls-Royce Cars (TSD publication 2066), Chapter ‘J’ Brakes by Rolls-Royce Motors
Rolls-Royce Small Horsepower Brake Systems by R. Haynes, published by RREC 1983
RREC Bulletins:
No. 6, pp 2–3 The Rolls–Royce Mechanical Servo by Nigel H. Hughes
No. 31 , pp 11-12. Adjustment of Servo Motors – All Models by R. Haynes
No. 96, pp 14-18. Overhauling your Servo by R. E. Kirby
No. 119, pp14-15, Servo Overhaul – late 20hp chassis GVO74 by Nick Jago
No. 149, pp 55-56, Servo Braking by Donald Bastow (correspondence)
No. 149, p 56, Brakes – Yet again by D. Stewart Watson (correspondence)
No. 149, p 56, Servo Operation by G. Ashley-Carter (correspondence)
RREC Technical Manuals:
1972, pp 172,173,170-171.
1978, pp 70-76.
RROC Flying Lady:
September 1969, pp 1198-1200, Servo Brake System- How it Works by Richard C. Hitchcock
November 1969, pp 1212-1215, Servo Adjustment and Overhaul Pre-War Cars by
R. E. Kirby with notes by R. Haynes.
January 2000, pp 5934- 5939, The R-R Servo on Small HP Cars by Gil Fuqua
The Hyphen in Rolls-Royce – The Story of Claude Johnson by Wilton .J Oldham
Once again I cannot speak highly enough for the advice and encouragement I received from John Hibbert, Stephen Wragg and Matthew Pickles, local experts in the marque.
Workshop Hints April 2013
Rolls-Royce Brake Servo
Rolls-Royce 25/30 chassis no: GRP29 Image references shown in blue
Headline image; GRP 29 at Chatsworth Country Fair, September 2012
Photograph by Sally Botham Estates
Background
The celebrated Rolls-Royce gearbox-driven servo assisted four-wheel braking system was introduced in the 1920s for the large ‘New Phantom’ model, destined to replace<
