Ferguson 4WD

Ferguson Formula Four-Wheel Drive Vehicles (April 2024)

Ferguson Formula Four-Wheel Drive Vehicles (April 2024)

The story of Ferguson Formula Four-Wheel Drive is told in this article, ‘After the Tractor’ Harry Ferguson & the R5 4WD; (See article below) Here is a list of most of the vehicles made by the three companies involved, Dixon-Rolt Developments Ltd., Harry Ferguson Research Ltd., and FF Developments Ltd. up to 1994


  • Research cars, built by Dixon-Rolt Developments Ltd or Harry Ferguson Research Ltd
  • Formula 1 cars, single seat racing cars and sports racing cars
  • Indy cars
  • Limited production or production cars built by other companies with components supplied by Harry Ferguson Research or FF Developments
  • Vehicles converted by Harry Ferguson Research, FF Developments or GKN as prototypes or special conversions for private customers
  • Vehicles converted by Harry Ferguson Research, FF Developments or GKN as limited production runs
  • Proof of concept vehicles built by FF Developments, or vehicles for which transfer case components were supplied by FF Developments
  • 4WD vehicles engineered and built by other companies using FF technology


*Indicates vehicle or vehicles’ whereabouts unknown, or not known to have survived
**Indicates vehicle is understood to have been scrapped

Research Cars built by Dixon-Rolt Developments Ltd or Harry Ferguson Research Ltd

Dixon-Rolt Crab
R3E **
R3G **
R3F (RPE 4)
R4/2 **
Ferguson-Climax F1 car, P99
Note: RPE 4, the car commonly referred to as R4, which is on display in the Coventry Motor Museum is actually R3F

Formula 1 cars, single seat racing cars and sports racing cars

Lotus 56B
Felday 4
Felday 5
Hepworth-Ferguson Guyson Sandblast Special
Matra MS84**

Indy cars

Novi-Ferguson P104
Granatelli-Novi 4WD **
Paxton Turbocar
Lotus 56/1, 56/2, 56/3, 56/4

Limited production or production cars built by other companies with components supplied by Harry Ferguson Research or FF Developments

Jensen FF
Schuler Super Ranger
Ford RS200

Vehicles converted by Harry Ferguson Research, FF Developments or GKN as prototypes or special conversions for private customers

Fiat Panda 4×4 VT *
Ford Capri Mk1 facelift (green)
Ford Capri II (black)
Ford Custom 500*
Ford Mk4 Zephyr estate (ex- Pat Hall)
Ford Mk4 Zodiac Estate (ex- Tony Rolt, aka ‘The Shed’)
Jaguar XJ6 V8 FF *
1965 Ford Mustang Tudor
1966 Ford Mustang Tudor*
1968 Ford Mustangs (believed 2) built for Borg-Warner*
1968 Ford Mustang Cobra Jet
1968 Ford Mustang Super Mach I *
1971 Ford Mustang Boss 305 convertible *
Jensen FFF100*
Reliant Scimitar GTE (GKN)
Triumph Stag (automatic)
Triumph Stag (manual)
Triumph 2.5PI Estate
Triumph 2.5PI estate with Stag engine
Triumph 2.5PI saloon*
Plymouth Fury Police car*
Ford Fairlane Police car*
Volvo 144*
Volvo 164*

Vehicles converted by Harry Ferguson Research, FF Developments or GKN as limited production runs

Bedford CF 4×4
Opel Senator, MVEE**
Opel Senator, civilian**
Ford Capri Mk1
Ford Capri Mk1 (German built)
Ford Mk4 Zephyr saloons, including police cars *

Proof of concept vehicles built by FF Developments, or vehicles for which transfer case components were supplied by FF Developments

AMC Eagle
BMW 323iX
Buick Century, 1985
Chevrolet Astro / GMC Safari 4×4
Fairchild-Hiller (New York) Safety Car
Ford Sierra 4×4
Fiat 128
Jaguar XJ220 4WD
Mazda 323GTX
MG Metro 6R4
Opel Manta B Group B rally car

4WD vehicles engineered and built by other companies using FF technology
(including Viscodrive and Ford Europe, GKN, Steyr-Daimler-Puch and Tochigi Fuji Sangyo)

Audi quattro Sport S1 (final, 1986 Group B version only)
Audi R8
Audi V8 quattro
BMW 325iX
Ford Escort Cosworth Turbo
Ford Sierra XR4x4/Cosworth 4×4
Ford Granada Scorpio 4×4
Jeep XJ Cherokee
Jeep WJ Grand Cherokee
Jeep ZJ Grand Cherokee
Lamborghini Diablo VT
Lancia Delta S4
Lancia Delta HF 4×4 and Integrale
Land Rover Freelander
MG Metro 6R4
Nissan Pulsar/Sunny GTI-R
Peugeot 205 T16
Peugeot 405 T16
Peugeot 405 Mi16 4×4
Range Rover Classic, 1989-on
Renault 21 Quadra
Renault Espace Quadra
Subaru Legacy
Subaru Rex
Toyota Camry
Toyota Celica GT4
Toyota Vista
Volkswagen Golf Syncro
VW Passat GT Syncro
Volkswagen Transporter Syncro
Volvo 850 T4 4×4
Volvo XC90 (first generation)

Photographs of many of these vehicles can be found Below:-

‘After the Tractor’ Harry Ferguson & the R5 4WD

Duncan Russell looks at the development of four wheel drive and Ferguson Research. (Duncan’s article from From Journal 64, Spring 2010 has been kindly updated by Bill Munro (author of “Traction For Sale”) in October 2023, the update is below……..

Prior to the article here is an interesting video of the Ferguson flat-4 engine; It’s the only fully-operational Ferguson flat-4 engine, demonstrated at the launch of Traction for Sale at the British Motor Museum, Coventry on 12th May 2019.

The engine has a single overhead cam par bank, driven by a toothed belt. This is believed to be the first known application of a belt drive to a camshaft, though not in a production engine

Bill Munro looks at the work of Harry Ferguson Research in the field of full-time Four-wheel drive.

During the 1930s, racing driver Fred Dixon was saddened by the growing number of deaths caused by road accidents and he hatched an idea to design a super-safe family car with four-wheel drive and four-wheel steering. When he raced at the Ulster TT, his car was garaged by Harry Ferguson and the two men would discuss Dixon’s ideas at length.

Dixon’s fellow racing driver, Tony Rolt acquired an ERA racing car in 1937 and he engaged Dixon as his racing mechanic. Intrigued by Dixon’s ideas, Rolt put up some money to form a company, Dixon-Rolt Developments Ltd to pursue the work and in a workshop behind Dixon’s house in Reigate, Surrey they built a prototype, which they called the Crab. It had four-wheel drive and four-wheel steering, but it could not be steered and braked at the same time. Clearly, much more work needed to be done. Rolt was a serving army officer and when war broke out in 1939, he was sent into action in France, was captured in the retreat to Dunkirk and ended the war in the infamous Colditz Castle. When he returned to England, he met up with Dixon and the two restarted work on the Crab.

The ‘Crab’, Dixon and Rolt’s first attempt at a 4WD Vehicle.

Rolt knew that Dixon-Rolt Developments needed capital. Harry Ferguson had won £9m in a landmark patent infringement case against the Ford Motor Company and in 1952, Rolt approached him to see if he would be willing to invest in their company. Instead, Ferguson bought the company and renamed it Harry Ferguson Research Ltd. New premises were found in nearby Redhill and design engineer Claude Hill was recruited from Aston Martin. A second prototype was developed, numbered R2, with a vertically mounted 4-cylinder Scotch Yoke engine at the rear. After testing it at Abbottswood, a pressed steel body was built for it. However, Dixon’s original four-wheel drive system didn’t control wheelspin, as it needed to do. Thinking hard on the problem, Harry Ferguson said, “what’s wanted is a diff that diffs when it should diff, and doesn’t diff when it shouldn’t.” He gave Claude Hill the task of making that a practical reality. Hill devised a mechanically controlled centre differential that locked when wheelspin was detected and immediately unlocked when traction was regained. That was the heart of what was, at first called the Ferguson Principle.

Meanwhile, Ferguson moved the company to his tractor factory in Coventry, which Dixon disagreed with and he left the company. At Coventry, a new four-wheel drive prototype, R3 was developed, fitted with a fibreglass estate car body and a flat-4 engine of the company’s own design. The plan was to offer the complete package to a major motor manufacturer to build under licence, in the same way that the tractors had been built, but no manufacturer was willing to take up the offer.

In 1954, Ferguson, having parted company with Massey-Harris was obliged to move Harry Ferguson Research out of the Coventry works. A temporary home was found at Chipping Warden airfield, where a further research car, R3F was built, using a platform chassis and the R2’s body crudely modified to accept the totally different mechanical components. This was registered as RPE 4, though later, erroneously referred to as R4. It is now on display at the Coventry Transport Museum.

Ferguson R3F, an interim research car using the body built for R2 and using a Ferguson flat-four engine, mounted on a platform chassis.

A total of three prototype road cars were built, two estate cars and a saloon.

Ferguson Research Car R3F as it is today, on display at the Coventry Transport Museum

Ferguson built new premises at Siskin Drive, Coventry in 1956 and there, in 1959 work began on a fourth generation Research Vehicle, R4, with a similar platform chassis to that of R3F and an estate car body designed by Giovanni Michelotti. A year later, work began on what is perhaps the most famous Ferguson four-wheel drive car of all, the Ferguson-Climax Grand Prix car, P99.

Ferguson R5 Estate car prototype; One of two Ferguson R5 Estate cars built. Both survive, in the possession of the Coventry Transport Museum

The Ferguson P99 with Stirling Moss at the wheel, testing at British Grand Prix 1961.

P99 conformed to the new Formula I regulations for 1.5 litre cars, but all this generation were rear-engined and P99’s handling advantage was much less than it was with the older front-engine cars. P99’s racing programme was run by Rob Walker Racing and its first race was the British Empire Trophy Race at Silverstone, with Stirling Moss as the driver and Jack Fairman as reserve. However, brake failure forced retirement. It was entered for the 1961 British Grand Prix at Aintree. After practice, Moss, prioritising his championship chances, considered that the car was not developed sufficiently to be a serious contender and started the race in a Lotus. Jack Fairman started the race in very wet conditions, but after the car developed a misfire, which was fixed, Moss took over and brought the car up to second place. However, he was black-flagged because the car had been push-started. Moss drove P99 in the Oulton Park Gold Cup race in 1961 where the damp conditions suited the four-wheel drive and Stirling won by some considerable margin. It was the first and only Grand Prix win by a 4WD car.

Sadly, Harry Ferguson did not see P99 compete. He died in 1960 and the chairmanship of the company passed to his son-in-law, Tony Sheldon. A further research model, R5 was developed, as an estate car with a 2-litre overhead cam version of the flat-4 engine. Two examples were built, the grey R5/1, which later was fitted with a Paxton supercharger, and the blue R5/2. Both survive in the Coventry Transport Museum warehouse.

Tony Sheldon scrapped Harry Ferguson’s original plan, to offer a complete vehicle package and instead the company began developing a range of systems that could be offered to car makers for fitting to their existing cars. At the time, only one maker, Jensen took up the offer, introducing the 4WD Jensen FF (for Ferguson Formula). This was also the first production car to incorporate the Dunlop Maxaret anti-skid braking system, which was now an integral part of the Ferguson Formula.

In 1969, GKN bought into Harry Ferguson Research and acquired the rights to mass-produce the four-wheel drive systems, which promised to bring down the cost of the four-wheel drive systems dramatically. However, when a plan to build a four-wheel drive version of the new Ford Capri using GKN-built components fell through, Tony Sheldon pulled the plug on the research work and in 1971 the company was closed.

Just before the closure, a new type of control system for the centre differential, the Viscous Control, or VC was invented, which was far cheaper to build than the old mechanical unit and totally reliable. Tony Rolt believed this was the route to success and with Sheldon’s blessing formed his own research company, FF Developments Ltd. In the late 1970s, after several attempts to sell the system to the motor industry, American Motors took up the Ferguson Formula, with the VC, for its new all-wheel drive Eagle. This was the first mass-produced car with full-time four-wheel drive, beating the Audi quattro to market by a matter of weeks. Ford then took up the system for the Sierra and Scorpio 4×4 and Ferguson’s four-wheel drive system, in various guises was adopted by many makes around the world, including Volvo, Audi, Subaru, Lamborghini and Volkswagen. In 1994, FF Developments was bought By Ricardo Plc and is now Ricardo’s Driveline and Transmission facility.

P99 is now in the custody of the Rolt family. It was raced in historic events until 2017 but is now only driven in demonstration events.

Originally published in Journal 64, Spring 2010, Duncan Russell – updated by Bill Munro – October 2023

‘Traction for Sale’, Ferguson R5 4WD

Traction for Sale Mike Thorne

Tim Hanson, your editor, suggested that I write a review of this handsome new publication written by Bill Munro and Patricia Turner. Traction for Sale is the story of Harry Ferguson and his team in their development of permanent 4WD drive systems for road vehicles, this included their own prototypes and the conversions to 4WD of some mass produced cars and vans. Also embraced in this story are the developments they pioneered in racing cars: this was the era of Harry Ferguson Research (H.FR.) later to become Formula Ferguson Developments Ltd. (FFD) and eventually Ricardo FFD. Harry Ferguson’s interest in producing a ‘Safer Car for the Masses’ dates back before the merger with Massey Harris but unfortunately he did not live quite long enough to see the success of his 4WD Racing Car. Following his death in October 1960 the business was headed up by H.F’s son-in-law, Tony Sheldon with the able assistance of Tony Rolt (former Team Jaguar Racing Driver).

It cannot be over­emphasised that it was Tony Rolt who was the driving force in all this experimental work, right from the early days of Dixon-Rolt Develop­ments, the HFR era and well on into the days of Formula Ferguson De­velopments Ltd., which was in fact Rolt’s own company, with no direct business connection with the Ferguson Family Trust.

This book had a long gestation period. Bill Munro first became interested when, during his research into Jeeps in 1998, he contacted Ricardo FFD (formerly FF Developments) and met one of their long time engineers, Will Turner, whose wife, Patricia, had previously written an unpublished history of Harry Ferguson Research. It was suggested that Bill should make use of this and so the seeds were sown.

‘R5′ OWK 21 was the last Ferguson research car to be built before the company changed direction and began to adapt the technology to fit other makers’ cars.

I jumped at this opportunity to write a review as I have a strong interest in all H.Fs pioneering work not only his developed of the Ferguson System but the work he and his team became involved with, later in his life, to engineer safer road cars with the inclusion of 4WD and anti­locking braking systems.

This hardback book runs to 350 pages, profusely illustrated with archive photo­graphs and line drawings. It is clear that Bill has done much in-depth and wide ranging research and the manner in which he has presented this is evidence of his fascination with the subject and dare I say addictiori. I have found this book compulsive reading.

‘R3C’ is the third generation research car, pictured with Major Tony Rolt in the garden of Harry Ferguson’s home at Abbottswood, Gloucestershire.

The book is very detailed and I feel I can give you a flavour of this with the follow­ing bullet points taken from the back cover:-

  • In a story spanning seven decades, Traction for Sale tells of the efforts made to bring Ferguson full time four wheel drive to the mass market.
  • The Story of Harry Ferguson Research Ltd in developing the Ferguson Formula of All-wheel Control.
  • Full story of the Ferguson research cars.
  • The story of F.F. Developments, the comp­any founded by Tony Rolt to take the tech­nology forward when the estate of Harry Ferguson ceased to fund any further research.

Details of:-

  • Leading production cars: The Jensen FF, AMC Eagle and the Ford Sierra XR 4X4
  • Converted cars: The Ford Mustangs, Ford Zephyr MK4 and Capri, the Schuler Super Ranger and Opel Monza and Senator.
  • Formula One cars: The Ferguson Climax P99, BRM P67, Matra MS84 and Lotus 56B.-
  • Indianapolis cars: The Novi-Ferguson cars, the Paxton Turbocar and the Lotus 56.
  • Peter Westbury’s: Felday 4 and Felday 5 sports racers.
  • Group B rally cars: Peugeot 205T16, Lancia Delta S4, Ford RS200 and MG Metro 6R4.
  • Other vehicles that either made it into full production or never got beyond the planning stage.
  • Non four wheel drive work carried out by H.F.R. and transmissions contracts fulfilled by FF Developments.

To summarize I feel this book is a ‘must have’ for anyone who is stimulated by pioneering engineering concepts and is also another insght into H.F’s versatility. There was much more to him than just the ‘Little Grey Tractor’. When this work started, 4WD was generally confined to military and off-road vehicles. The philosophy behind all this development work was to engineer a safer road car for everyone. Today, of course, 4WD is almost common place.

The forward to Bill’s book is written by the Duke of Richmond and Gordon, his concluding paragraph is, in my opinion, spot on. ‘This is a great story, told in the kind of detail that will appeal to all of those who appreciate inventive engineering’.

Here is a link to Bill Munro’s website with details of how to buy copies of the book (and others) at preferential rates…..

Welcome to Earlswood Press – Earlswood Press

© Mike Thorne, First published in the Ferguson Club Journal, Issue 93, Winter 2019/20

The Ferguson R5 Prototype

The Ferguson R5 Prototype

Photograph, Ferguson Research Archives.

The anti-spin and anti-lock mechanisms described by Charles Bulmer B.Sc., A.F.R.Ae.S.
Dual-purpose – a car intended to set new standards in road­-holding and road safety and yet to have traction. ruggedness and ground clearance making it equally at home off the road.

We described the Ferguson single-seater racing car in July, 1961, and the estate car prototype, forerunner of the models featured in our road test, later in the same month. Since that time the special Ferguson features and principles have remained basically unaltered but there has been a great deal of development; these changes, which are found mainly in the transmission and brakes, we shall describe below to bring the story up to date, but before doing so it would be as well to outline very briefly the reasons why the car takes the particular shape and form it does.

It will be remembered that four-wheel drive is an essential part of the design and this demands a longitudinal propeller shaft extend­ing from front to back. Clearly. the engine is then most easily accommodated if it goes right at the front, ahead of the front final drive unit or right at the back behind the rear drive; it could. of course, go anywhere between if it were mounted above the shaft but this would be less economical of space and probably raise the centre of gravity.

Now with the Ferguson transmission it makes no difference to traction or braking power which end you put it-most of the old arguments in favour of one arrangement or the other become in­valid. There remains, however. the effect of weight distribution on road holding and cornering; with a forward weight bias stability on the straight, in cross-winds and on corners is easier to achieve without resort to extremes in suspension design which usually carry undesirable penalties and side-effects.

So the engine was put at the front, leaving the maximum accom­modation for luggage and also making it possible to use a body of estate car pattern with a low rear floor level; a type which many designers now regard as the normal family body of the future. With this layout an engine of minimum length is desirable to reduce front overhang and of minimum overall height for forward visibility and to harmonize with modern low-fronted styling. Both considerations suggested a flat four or six and for an engine capacity around 2.2­litres, the former was thought entirely adequate.

Regarding the Ferguson as a car designed for the near future. it would have been an anachronism to have anything but independent suspension all round, or a near-equivalent like de Dion. The front suspension is by the usual unequal length transverse wishbones with coil spring/damper units mounted very high and bearing on the outer part of the upper wishbone, very much like the Triumph 1300. Rear suspension is shown in Figure 1I. Geometrically it is closely related to the almost standardized type used by modern Grand Prix cars: mechanically it is engineered in a sturdier way more appropriate to a touring vehicle.

fig.1 The Independent rear suspension is strong but simple.

Ordinary cross-ply tyres were used at first but when it became clear that radial-ply covers offer higher cornering power, higher cruising speeds at standard pressures without overheating and better grip on slippery surfaces. a car dedicated to safety could hardly ignore them. Adapting the suspension to accept their dif­ferent characteristics without excessive harshness and road noise has been a development headache.

fig. 2 Engine and transmission layout.

A steel body/chassis unit of conventional construction com­pletes the design, the general layout being shown in the plan-view drawing (Figure 2). We have made no attempt to describe the car in great detail because its main purpose is to provide a vehicle of sufficiently modern design and performance to demonstrate the virtues inherent in the transmission and braking systems.

fig. 3 The actual inter­relationship 01 the various transmission components is illustrated in this diagram and described in the text. Note the Maxaret unit on the extreme right.

This is best described in two separate parts-first the semi-auto­matic gearbox and then the four wheel drive and special centre-­differential assembly. The whole assembly is shown diagrammatic­ally in Figure 3.

From the engine flywheel, the drive goes directly to the Ferguson ­Terramala hydraulic torque converter which has an unusually wide conversion range–it can give torque multiplication ratios as high as 2.7-3 when starting from rest. ,In previous designs a two speed epicyclic gearbox (like an overdrive) was interposed between the engine and the converter, an unusual arrangement with interesting characteristics but rather expensive.

Ferguson estimate that to add a torque converter to a conven­tional synchromesh gearbox involves only half the extra cost of replacing it with a fully automatic transmission, particularly as the gap-bridging effect of a converter makes it necessary to have only three speeds instead of four.

This, as the drawing shows, is what they have done. A conven­tional foot-operated friction clutch is retained between the two to separate them for gear changing-otherwise gear changing on the move would be impossible or very destructive–but, of course, this clutch need not be used for take-off from rest. The car can there­fore be driven as a two pedal vehicle (in one gear) in towns or open country or a three pedal machine for maximum performance but, in any case, the wide-ratio converter reduces to a minimum the necessity for gear changing.

The Centre Differential
The offset between the gearbox output shaft and the drive shaft line is bridged by a twin duplex Reynolds roller chain drive running

at very high efficiency in; an oil bath. This chain drives the planet cage of an ordinary differential and the two sun wheels are con­nected to the front and rear final drives respectively. Up to this point, therefore, we have an ordinary four-wheel drive system delivering equal torques to front and rear but with nothing to stop the wheels at one end spinning.

The special feature of the Ferguson drive is best illustrated by a simplified diagram (Figure 4).

Fig. 4 (above) This shows the basic principle (not the actual layout) of the Ferguson differential. The drive is transmitted through the central gear set. To the differential cage: the other two gears on the two output shafts are driven at a higher speed and idle on their free·wheels. But if either shaft accelerates to the same speed as the gear revolving on it. The free wheel locks and prevents any further increase.

This shows the main drive taken from the input shaft to the differential cage, as before, but in addition two more gears of different ratio are also connected from the input to the output ·shafts. This can only work because the gears on the output shafts are mounted on free wheels (one-way roller clutches) which allow them to rotate at higher speeds. If, however, either of these output shafts speeds up to the same r.p.m. as the gear running on it, the free wheel will lock up solid and prevent any further increase. So the centre differential will allow the front wheels to rotate faster than the back (or vice versa) but only between certain limits of rotational speed dictated by the ratios of the two additional gear sets.

In the Ferguson car this principle is retained but the layout is different (Figure 3) in that the control gears and clutches are physic­ally sited all on one side of the centre differential; this is more con­venient because of the large centre distance between input and output shafts. In this application the gear A is driven directly from the differential cage, the front drive propeller shaft passing freely through the middle of it. It follows then that A and B and the whole “duolok” layshaft are in effect coupled directly to the input from the gearbox; by using the two free-wheeling gears on this layshaft to control the speed of the front propeller shaft within limits (which will be a little more or a little less than that of the differential cage) exactly the same effect is achieved as with the simple system of Figure 4. In this case the free wheels will operate in opposite rota­tional directions; for reversing they have to be put out of action altogether otherwise they lock up solid.

So for steering purposes or to accommodate variations in tyre diameter one pair of road wheels can rotate slightly faster than the other but as soon as one or more wheels try to spin, the control action comes into effect by prohibiting the large relative speeds involved. It is, of course, still possible to spin all four wheels or, in special circumstances, to spin one front and one back wheel simultaneously.

On slippery corners splitting the driving load between all four wheels enables a skilled driver to use a great deal of power without any danger of producing a sudden breakaway at one end of the car-perhaps more to the point it enables an unskilled driver to be as ham-footed as he likes in these circumstances without dire results. Although the arrangement we have described gives a 50/50 torque split between front and rear wheels, this is not an essential feature of the design and by replacing the ordinary centre differ­ential with one of different pattern it is possible to divide the torque in other proportions. The Jensen FF, for example, has an epicyclic differential passing 63% of the drive torque to the rear and 37% to the front; in this way normal handling characteristics can be modified without prejudicing the speed limiting effect which will override other considerations when abnormal (incipient wheelspin) conditions are reached.

Now the intercoupling of front and rear operates, of course, in deceleration as well as in acceleration. It is not effectively possible for a single whee to lock unless all four do so or, at the very least, unless another wheel locks at the other end of the car. But either of these occurrences can be prevented entirely in normal circum­stances by the Dunlop Maxaret control unit-Figure 3 shows its location in the Ferguson layout.

Braking system
We have described the Maxaret unit before on several occasions. It contains a small flywheel which is driven (in this application) at input shaft speed (or at some fixed fraction of this speed) by a spring drive of limited torque capacity. A sudden angular decelera­tion, of the kind which accompanies wheel locking, collapses the spring drive and the relative (angular) movement between the flywheel and its drive shaft is used to operate valves which auto­matically unload the brake hydraulic line pressure before locking actually happens. In this way the braking can be controlled to oscillate (or “cycle”) around the region of maximum braking without allowing rotation to stop.

In the form used by aircraft for many years, each landing wheel has its own Maxaret operating independently on the very high pressure hydraulic supply to that wheel. The centre differential of the Ferguson allows one Maxaret to operate all four brakes since, as we have already pointed out, single wheel locking is prevented. This means a considerable saving in cost. But in its original form it still needed the high pressure hydraulic supply which cars in general do not possess (Citroen and Rolls-Royce are exceptions) and which would be very expensive to fit.

The development of the system to ‘use a vacuum servo and ordinary direct hydraulic brake operation is the significant accomplishment of the last few years in evolving towards a design which is economically as well as technically possible; the current layout is shown in the simplified diagram of Figure 5.
fig. 5 The latest, much less expensive braking system has been developed to work with an ordinary vacuum servo instead of a high pressure powered hydraulic system.

The brake pedal acts directly on a tandem master cylinder feeding separate front and rear brake hydraulic circuits. A large direct acting servo – a standard Kelsey Hall unit made under licence by Dunlop – is coupled to the pedal operating rod. All this is standard practice.

In the “off” position vacuum is present on both sides of the Servo diaphragm because the two chambers A and B are in direct communication through the drilled passages and plate valves in the centre of the servo unit. First operation of the pedal seals off this connection and further pressure then pushes a plate valve off its seat to open a connection between C and B. Now C. at this stage, is at atmospheric pressure because it is. in communication with the right hand chamber of the control unit and this in turn is connected to atmosphere via the pipe running below it in the diagram.

So air is admitted to chamber B and the servo diaphragm IS pushed to the left, assisting the driver’s own efforts on the pedal; the valve between Band C is so balanced that it closes agam when the servo force reaches a certain value and in this way the assisting force is kept strictly in proportion to the driver’s own efforts. This, of course. is ordinary servo operation because at this stage, as indeed for all normal braking, the Maxaret control is inactive.

As soon as a wheel starts to lock the Maxaret contacts close and it sends an electrical signal to energize the solenoid in the control unit. This moves the double shuttle valve from the position shown (at the right-hand end of its travel) hard over to the left which cuts off the connection between the vacuum reservoir and chamber A and transfers it instead (via the control valve) to C and thence to B: at the same time A is connected to atmo­sphere so that the net result of the Maxaret intervention is to reverse the pressure and vacuum conditions on the servo diaphragm. It then pushes against the driver’s foot, forcing the brake off again until such time as the “locking” signal ceases and the solenoid allows the control valve to return to the right hand position under spring loading.

. In practice these alternations of pressure and suction across the two sides of the diaphragm will occur very rapidly-several times a second-to keep the brake hydraulic pressure fluctuating around the value which just corresponds to the locking peak. If the driver pushes harder still on the pedal, the servo will oppose his effort more strongly to keep the net force on the master cylinder the same.

There are a number of refinements and fail safe devices in the system. For example, a connection is shown to the lower part of chamber B through a non-return valve; this is not essential but it by-passes the valves and small passages between Band C and greatly speeds up the rate of pressure changes. Then there is a threshold pressure switch in the front brake hydraulic line which isolates the whole system electrically until the pedal is pressed and a little hydraulic pressure is developed. This prevents the Maxaret from energizing the solenoid in response to jerks in the transmission which can arise from gear-changing or even from exceptionally bad bumps or potholes. The latest developments are beginning to make this pressure switch redundant.

If a fault or short circuit developed either in the Maxaret or in the external wiring: in such a way that the solenoid was energized inadvertently; it would be dangerous because the brakes would then be held off \\’ith full servo force. At the right-hand end of the control unit is the fail-safe valve which in these circumstances would experience a vacuum to the right of the small plate valve and atmo­spheric pressure to the left of its diaphragm; the areas of the valve and diaphragm are so calculated that the differential load across the valve would then be just sufficient to move it to the right against the seating provided, cutting off the vacuum supply to the servo diaphragm. Since similar differential pressure conditions can exist for short periods in ordinary Maxaret use, a deliberate delay IS built into the operation, the air to the left hand side of the fail-safe diaphragm being supplied through a very small restrictor so that it needs about half a second for the pressure to rise high enough to push the valve across.

Facts and fallacies
Perhaps the impression has got around that the Ferguson­ Maxaret combination is infallible-the complete answer to all skidding problems and a device which makes brakes super­-normally effective. This is only true up to a point and .it is certainly a wider claim than its sponsors would make for It. It might be as well to look more closely at its limitations as well as its virtues.

Its greatest virtue is safety because on all normal. wet or dry road conditions, both on the straight and on corners, It w1l1 allow even a novice driver to react to an emergency in the most panic­-stricken way without losing control of the car. We needn’t stress this point any more because it emerges clearly enough from. the road test. As regards actual stopping distances, it makes little difference from very low speeds or even from high speeds on dry roads. On wet roads it is a different matter; on May I, 1965 we published some figures and graphs showing the tremendous difference in the available coefficient of friction between tyre and road just before and just after the wheel locking point which may differ by a factor of 2 to I; the Maxaret can keep the wheels oscillating around peak grip but no driver, however skilled, can do so. So the higher the speed and (up to a point) the more slippery the road the more dramatic the gains it can show.

It is not, however, really effective in such conditions as ice and snow. There are various reasons for this; the Maxaret unit has to allow quite rapid wheel deceleration on dry roads without coming into operation-the sort of deceleration that corresponds to a 1g stop with rotating wheels – only at appreciably higher angular decelerations should it send a distress signal to thee solenoid. On ice. wheel accelerations and decelerations tend to be low because of the small amount of braking used and the low grip. A Maxaret can be designed for these conditions but only by prejudicing its behaviour on surfaces with coefficients in the region of 0.25 to 1, on which the average motorist drives for nearly the whole time. At present an attempt is being made to extend this range by the use of the all-weather valve; we shall not describe this in detail but it acts as a variable restrictor in the line to chamber A, altering its own restriction in accordance with the vacuum in the line in order to slow down the re-applica­tion of the brakes. It is able to discriminate between road condi­tions because in dry weather you need little vacuum to take the brakes off sufficiently-in wet weather you need a lot more.

There is one other limitation in exceptionally slippery con­ditions and that is the possibility of “pushing through” against maximum servo resistance. For example, taking· the servo diaphragm area as 48 sq. in. and the maximum available depres­sion as 10 Ib/sq. in., then the greatest force which the servo can exert against the driver is 480 lb. or, allowing for a mechanical brake pedal leverage of about 3 to I, say 130lb. at the pedal. Since a strong driver may be able to exert 200 lb. in a panic, he could in fact overcome the servo and still apply a respectable braking effort. There are obvious ways of changing the para­meters to reduce this possibility but with production servos and master cylinder sizes giving adequate fluid volume it is not as easy as it would seem.

But even here, as in all slippery conditions expected or un­expected the brake system operates as an early warning device; a driver of any sensitivity will be warned by an early “kick-back” on the pedal that things are not what they seem to be.

First published in Motor magazine.  Published in Journal 32, Autumn 1999.  Charles Bulmer B.Sc., A.F.R.Ae.S.

The Ferguson P99 Racing Car

When Stirling Moss led from the front.

IN a fortnight in which Formula One teams are flaunting their new designs and technical quirks, it is interesting to look back to when Stirling Moss made racing history, outdriving the field in the rain to win the non-championship Formula One Gold Cup at Oulton Park in 1961 in the revolutionary four-wheel ­drive Ferguson P99.

It was the first and only Formula One race won by a four wheel drive car and also the last Formula One race won by a car with the engine in the front.

Irish tractor millionaire, Harry Ferguson, championed the cause of four-wheel drive and his research and develop­ment company built a Formula One car to demonstrate the advantages of all-wheel traction but it was too late. Front­-engined cars had been superseded.

The previous two world titles in 1959 and 1960 had been won by rear-engined Coopers, so the Moss victory in the Ferguson was a hiccup in history, but his­tory nevertheless.

The car had three differentials: front, rear and a mid located differential that would lock if either the front wheels or the back outsped each other. Moss was fascinated by the Ferguson.

‘”It was completely different to driving a rear-engined car, and obviously the fact that all four wheels were driven and that there was power as well as cornering load being applied to the front wheels, asked the driver questions which initially perhaps he could not answer very intelligently.

Rob Walker had entered the Ferguson car for Moss at OuIton Park and he entered it again in the 1963 New Zealand series, fitted with a 2.5-Iitre four-cylinder Coventry-Climax engine.

Graham Hill. who was then the new world champion suffered clutch failure on the second lap of the New Zealand Grand Prix but soldiered on to within a lap of the finish before the transmission failed. Hill, exhausted and unaccustomed to the heat from the front-mounted engine, said it had been like racing a stove.

Innes Ireland raced the Ferguson to third place at Levin and at Teretonga, but the car expired with severe overheating on the Wigram airfield circuit. Every gauge that wasn’t reading 212 degrees was reading zero.” reported Ireland, also severely overheated.

The gallant old Ferguson is now on display at the Donington Collection.


Note: The Donington Collection has now closed.
“P99 is no longer housed at the Ferguson Family Museum on the Isle of Wight but is currently with the Rolt family. The museum still houses memorabilia, photographs. drawings and books etc. of the car’s history.” (Note on Ferguson Family Museum website June 2022)

Ferguson Prototype Flat Four Engine

Ferguson Prototype Flat Four Engine, Mike Thorne and Peter Smith:

Ferguson prototype Flat Four engine, designed to power the R5 Estate Car, developed and produced by Harry Ferguson Research Ltd (HFR).

This story started in 2012 when I received, out of the blue, a phone call from a gentleman based in Herefordshire, asking me if I would be interested in buying two prototype Ferguson car engines. One was an overhead valve unit, developed to power the R4 Ferguson car, while the other, the subject of this article, is an overhead cam engine, with toothed belts driving each camshaft. Yes, of course I was, but his asking price was far beyond my means and although he seemed very keen that they should come to the Coldridge Collection, I had to say sorry, I cannot afford to pay your asking price, and left it at that.

Well about ten days later he phoned me again with the suggestion that I may have a tractor that I would be prepared to swap for the two engines. My immediate response was yes, I have a MF165, fitted with a four wheel traction conversion in a rough, unrestored state, apart from the engine which was running quite well, all the sheet metal work was rusted out, but I had been able to buy some genuine replacement items second hand, so they were included in the swap. He was very happy with all this and a few days later he arrived with his 7.5ton 100TY with the two engines and a couple of boxed of various gaskets suitable for them. So we off loaded the engines and he drove the MF165 onto his lorry, strapped it down and set off back to Hereford.

The rusty and decaying engine as it arrived at Mike Thorne’s Coldridge collection.

I kept these engines in dry storage; they were viewed from time to time by interested visitors. One was a gentleman who had worked for HFR and he had been involved with the R5 project. It was he who told me that a batch of seven engines had been developed and built up, mine carries a commission plate marked P94/4 (project 94 number 4). He went on to tell me that on one, they had cut a piece out of the left hand rocker cover so that oil flow could be monitored, the cut was fitted with a perspex window. My reply was ‘that is this engine’!

Over time I have made a point of collecting any technical data relating to either of these engines. So far most of what I have been able to collect relates to the R5 engine, details of the earlier units seem to be more elusive. It is perhaps worth quoting here from one of these documents Automotive Engineer – March 1966 ‘A compact high performance 2232cc four cylinder horizontally opposed unit’ and a further quote ‘an engineer’s engine’. This power unit was designed by HFR chief engineer Claud Hill, an ex. Aston Martin designer. It was a very much developed follow on from the earlier OHV (push rods) that were installed in the Ferguson R4 car. Perhaps it should be mentioned here that Harry Ferguson Research was headed up at this time by Tony Sheldon, HF’s son-in-law, who took over following Harry Fergusons death in October 1960. Another aside is at one point in the development of the R4, the engineers were keen to road test it out, but their engine was not ready, so they decided to install a Jowet Javelin flat four OHV unit of 1.5 litres; by the way, the engine and the car were designed by their engineer, Gerald Palmer.

The specification of the R5 engine P94/4 is as follows:- Bore 95mm, stroke 78mm swept volume 2212cc, compression ratio 9:1, sump capacity 10pts of SAE 10/40. Its alternator is driven by a micro vee belt.

The first set of performance figures are taken from the Automotive Engineer dated March 1965 and are as follows: – max power output 125bhp at 5400rpm, max torque 131Ib/ft at 2500rpm, firing order 1,4,2,3. The second set of figures are taken from the Motor Magazines road test, dated August 1966 of the same engine i.e. fitted with two SU HD6 carburettors, max power 116bhp at 5400rpm, max torque 1281b/ft at 3500rpm.

The next part of this story started in the Summer of 2018 when Club members Julie Browning and Peter Smith visited the Coldridge Collection and Peter being a most competent motor engineer offered to rebuild this with his friend Robert McColl, needless to say I was delighted with this offer so the engine was loaded into their vehicle and they headed off back up to Cheshire.

Over now, to Peter Smith and Robert McColl to explain how with their skills and enthusiasm the engine was rebuilt to run­ning order, and a stand made to display it.

I first saw Mike’s Ferguson Research engines on one of our regular visits to Coldridge. After a look around the collection, Mike said that he had something to show us. In the back of the workshop there were two prototype engines. At a distance they looked quite complete and I said that “I didn’t think the overhead cam engine would take much to get it going”. How wrong can one be? So, after a little discussion, Mike decided that I would be the one to restore the engine.

Several years passed due to other commitments, but eventually the day came to collect the engine. We had been to the 2018 Dorset Steam Fair and on the way home we arranged to visit Mike and bring the OHC engine to Wilmslow. Rob McCall, a good friend of ours agreed to help me with the restoration of this engine and the whole process has been a joint venture between Rob and myself, with help from Dennis Williamson and lots of helpful advice from Julie.

As soon as we got the engine back to Cheshire, it became apparent that the task was going to be much larger that we first thought. The engine was seized and when the top of the air filter was removed, it was clear that rodents had been using it as a home for quite some time.

Whatever had been living in it, had, in the process, caused considerable damage to the aluminium carburettor bodies.

The first job was to secure the engine before dismantling it. We do have a good engine stand, but as the engine was to be displayed on a stand when completed, the decision was taken to make the frame first. 50mm box section was used for this purpose and Rob welded it all together. The design allowed for the engine to sit on the frame with all the ancillaries to be mounted to the right of the engine. This would allow for an unobstructed view of the engine. The frame also allowed for the sump to sit inside the stand for service and inspection.

Once the engine was safely mounted, the next job was to assess the cause of it being seized. The spark plugs were removed and a borescope was used to check on the state of the bores. The news wasn’t good and the decision was taken to carry out a full strip down.

The engine was completely stripped and it was reasonably easy to free off and remove the sized piston. It was at this point we were able to completely understand and appreciate the design of the engine.

The cylinders are paired front and rear. Both front pistons hit TDC together eliminating a lot of vibration. Throughout the rebuild we have noted several other unusual design features that are not often seen on engines of this era; The pistons themselves are of a complex design, shaped to match the internals of the cylinder head and valve arrangement for efficiency and performance. The rocker shaft mounting posts have one-way valves built in, presumably for maintaining oil pressure within the valve train. Due to the physical construction of a flat 4, the engine is effectively a “dry sump” arrangement relying only on pumped oil for lubrication to the crankshaft, we have no documentation to support whether this was at this stage merely a coincidence of design, or an intentional feature of Ferguson’s to reduce drag on the crankshaft. Perhaps most unusual of all for an engine of this period is the timing being controlled by two independent toothed belts, this at this time was very much in line with the emerging technology of the era and one report actually states that this was a first. The whole engine being a flat four would have had a low centre of gravity and would have suited a sports car/racing car.

The engine block was cleaned up and the cylinders were honed. The pistons were cleaned, but the rings were seized tightly within the grooves and could not be removed intact; so, a new set of piston rings were sourced. They had to be custom made as none of the piston ring manufactures had anything on the shelf that would fit the Ferguson engine, as they were of quite narrow gauge.

Mike had supplied a box of mixed gaskets. It soon became apparent that not all the gaskets were for this engine, but were probably of other variants of similar engines that HFR were working on at the time. Fortunately, we did find a good set of head gaskets that fitted.

The rebuild started and progressed quite well. Timing belts had already been sourced. The correct pitch was not available in the U.K. as it was imperial, but we were able to order a set from the U.S. and when the factory had enough special orders, they batched them.

Looking down on to the restored engine which shows its unique shape.

How to time the engine was still a mystery, due to a lack of technical data. When the flywheel was cleaned up, we discovered two sets of markings. One of these looked to be in the correct place for TDC. Camshaft pulleys had been marked on strip down as their bolt pattern and the lack of a locating dowel allowed the pulleys to be fitted in six different positions. Again, when cleaned up, there were also timing marks on the camshaft pull~ys. When all these marks were aligned, it became apparent that the engine frame had subtle timing marks and everything made sense. Even though everything looked obvious, the engine was rotated slowly by hand many times while observing the actions of the valves until we were completely happy that the engine timing was correct.

The next step was to create starter, fuelling and ignition wiring for the engine. It had come with a distributor, but little else. A control panel was fabricated onto the frame and to this all necessary components and switches to make the engine run. It was at this point a fuel tank and fuel pump were installed.

Due to the previously mentioned damage, a set of carburettors were sourced from a well-known internet auction site. They had to be stripped and checked over. New needles were fitted to the same specification as those in the original carburettors (which took considerable attention to remove). We hope these will give a reasonable performance, but it is my guess that Ferguson had tried many different needle combinations, as there is literature that suggests many different carburettor arrangements were trialled and tested on these engines.

Along came test day and the moment of truth. A battery was connected and a small amount of fuel put in the tank. It took three of four quick attempts and with a small adjustment to the distributor timing, it was running. This test was for about ten seconds as the engine still had no water in it, but it was successful.

An exhaust manifold was made from scratch. No silencer has (at time of writing) been fitted, but the hot gasses are now directed away from the engine. A radiator was fitted to the far right of the frame and hoses routed from the engine to the radiator. This allowed for a much longer test run.

Now knowing that the engine would run and with talk of its first public outing, we turned our attention to safety. A perspex guard was fitted to the front of the engine to protect the timing belts, but still allow full vision. To the rear a mesh guard was made to cover the flywheel.

The restored engine mounted to its new frame with the control panel to the top right.

Just to round off this article, I would like any interested person to feel free to contact me on 07966328600 to make an appointment to view the Coldridge Collection. Likewise Peter Smith and Julie Browning, who have an extensive collection of rare Ferguson tractors and implements, many from the American manufactory, would welcome visitors.

© Mike Thorne and Peter Smith, Ferguson Club Journal Issue 94, Spring 2020