Enthusiast's Directory -- No. 11 Brakes And Brake Linings
In post-war years the general motoring public has become much more performance-minded, from owners of the ever popular two-seater sports cars down to those with 8-h.p. family saloons. This has come about partly because of extensive wartime training of civilians in all forms of mechanised transport, the possession of motor cars by those who were previously not in a position to own one and, in the interests of safety, better acceleration and roadholding have been demanded.
To accompany this race for performance brakes and linings have come more into the limelight and both large and small manufacturers continue with research at top speed. Until the introduction of disc brakes on production models in recent months there have been comparatively few radical changes in braking systems and mechanisms, the accent being on continual improvement. Friction materials for brake linings, however, come up for stringent attention at all times; their evolution is largely dictated by the uses to which they are put, and these may vary depending on the type of vehicle, its normal kind of work, the requirements of the driver, the climate in which they must operate and so on. There are therefore many requirements to be met and for many years these have been met in spite of modern trends by way of faster and heavier cars requiring greater stopping power.
Brake linings can be divided into two groups, textile and moulded. Textile linings consist mainly of asbestos fibres woven into cloth and the moulded types consist of some asbestos fibres and many other heat-resistant materials being bonded together. Each type has its own range of characteristics and properties. In the case of disc brakes, however, it is likely that some change will take place since the demands made on friction materials used in this sphere differ from those of the drum brake. It no longer becomes necessary for the material to be bent to the shape of the shoe, small flat discs being required which reduce the difficulties in bonding, resulting in a material with greater heat-resisting properties and having fade-free characteristics, the chief advantage of the disc brake over the conventional drum types. Other advantages are their light weight and the easy replacement of the actual brake pads.
The previous ranges of hydraulic and cable-operated brakes manufactured by the respective companies still continue for use in vehicles operating under less exacting conditions. -- I. G.
Over fifty years ago when the use of the bicycle was spreading rapidly, and the motor car was not yet regarded, except by an inspired band of pioneers, as a serious proposition, the original Bowden Wire Mechanism was evolved. It took a long time for the merits of this system of power transmission to be recognised however, but the present-day "Bowdenex" cable is a very well known commodity in all forms of modern transport and plays a big part in many braking systems.
Ernest Bowden took out a patent for his wire mechanism in 1896 as a "Mechanism for transmitting power without pulleys, angle levers, ball joints and other usual mediums." First designed for bicycles this mechanism was used in conjunction with the Bowden brake, but later applications became varied in their fields of use. In order to convince motor-cycle manufacturers of the early 1900s of the effectiveness of brakes equipped with Bowden cables the firm marketed their own motor-cycle in 1903, and this machine was years ahead of its time with modern-type cable-operated controls. The same principles apply in "Bowdenex," which consists of the same flexible inner cable supported by an improved outer casing. "Bowdenex" is used extensively throughout the world for brake operation on cars and other vehicles.
Manufacturers: Bowden (Engineers), Ltd., Willesden Junction, London, N.W.10.
Producers of the popular Duron brake linings, Brake Linings Ltd. supply many varieties of friction materials for general use on industrial brakes and clutches and similar applications. A glance at their comprehensive catalogue reveals the large number of different types of material, what they are made of and their various applications.
Manufacturers: Brake Linings, Ltd., Buxton, Derbyshire.
The Cape Asbestos Company were amongst the pioneers in this country of heavy duty moulded brake liners and clutch friction facings. During the war years it became clear that post-war vehicle performance would alter to such an extent that woven linings would be incapable of producing adequate results, particularly from the point of view of resistance to fade.
Whilst considerable emphasis is placed on providing "Capasco" linings in the public service vehicle and heavy commercial vehicle fields, "Capasco" HF32 has been developed for light and medium private cars where a high coefficient of friction with exceptional resistance to fade is a criterion. This material has a rated coefficient of 0.41. "Capasco" HF33 is suitable for private car work having a rated coefficient of 0.42 combined with smooth frictional properties, coupled with good wearing properties. "Capasco" BR20 is produced for cars designed for medium friction facings such as those where the brake pedal is servo-assisted, and those where squealing brakes and fierce brakes need careful attention from the lining point of view. For the 100 m.p.h. car with brakes of 10 in. diameter upwards "Capasco" N47 combines a rated coefficient of friction of .040 with complete stability over the whole speed range of the vehicle and complete resistance to fade over the whole drum temperature range.
Manufacturers: Cape Asbestos Co., Ltd., 114 and 116, Park Street, London, W.1.
Makers of vacuum servo equipment, this firm has considerable experience in the commercial vehicle field and has been producing heavy duty units for installation in public service and other heavy goods vehicles for a number of years.
In keeping with modern demands Clayton-Dewandre are supplying their "Vom" servo units for use with the new disc brakes.
Manufacturers: Clayton-Dewandre Co., Ltd., Post Office Box No. 9, Titanic Works, Lincoln.
In recent years Dunlop have met considerable success with their disc brakes, which they have been perfecting for more than ten years.
Designed to meet the increased demands made on brakes for use on road transport and aircraft, Dunlop introduced a disc brake in 1945 in which the conventional drum was replaced by metal rings keyed into the wheel, with piston-operated friction pads opposed to contact the rotating rings when the brakes were applied. In the latest type for cars the operating pistons are contained in the separate cylinders contained in the caliper body, giving improved insulation of the pistons and seals from the heat generated during braking. These brakes are impervious to water and have self-adjusting pads which require no attention or maintenance, they have been thoroughly tested by racing drivers on some of the world's fastest race tracks and are now available on production models for the private motorist.
Manufacturers: The Dunlop Rim and Wheel Co., Ltd., Foleshill, Coventry.
Feeney & Johnson
Well known for many years for the manufacture of power equipment for vehicle brakes and hand-control conversions for disabled drivers. Feeney & Johnson vacuum servo mechanisms are of exceptional value in heavy goods vehicles where some form of power-operated braking is essential, but smaller units can be supplied for use on light trailers and caravans.
Another application is the use of the equipment on vintage cars which require heavy pedal pressures on the part of the driver for sudden stops. Feeney & Johnson can supply vacuum servo units for Bentleys, Lagondas, Aston Martins and other makes from stock or to special order at prices ranging from £12-£15, all of which would appear to be very good value.
Manufacturers: Feeney & Johnson, Ltd., 134-136, Ealing Road, Wembley, Middlesex.
The name of Ferodo needs no introduction to motorists. The types of linings produced by this well-known firm are too numerous to mention but a representative selection and their main uses would not be amiss. All these linings have been tested to rally standards and, although special materials are used when racing and competition work are envisaged, there is no advantage to be gained by using these special linings for normal road work when a suitable standard quality is available.
Here are some of the standard linings for drum brakes: --
MR41. Solid woven non-metallic. Little high temperature fade.
MR19. Solid woven non-metallic. Less fade resistance than MR41. More suitable for medium-sized cars.
MZ41. Similar to MR 41, but with zinc wire inclusion for conducting heat away from working surfaces.
DM1. Non-metallic rigid moulded. Suitable for Bendix brakes.
DM7. Moulded. High friction value. Suitable for light to medium cars.
DM8. As DM7, but with alloy chipping inclusions. High performance cars.
MS3. Rigid non-metallic. Anti-squeal properties. Suitable for bonding.
For disc brakes. DS1 and DS3 are manufactured.
The origin of Ferodo began towards the end of the nineteenth century, with a young man, Mr. Herbert Frood, who lived near Chapel and travelled daily to work in Manchester. Time and again he watched the carters struggling with their heavy loads and ineffective brakes and at last, his curiosity overcoming him, he inspected the brakes more closely. He examined the old boot which was a common replacement for the wooden blocks of the period.
Here, decided Frood, was a field for profitable research, and in a small wooden hut he started the experiment. He tried many materials and methods and finally produced a lining made from laminated hair belting impregnated with bitumen.
Tests soon proved it to be satisfactory and it was not long before he started a little factory in part of an old mill in Chapel. Very soon the demands for his product became so great that he took over the whole building.
As motoring became popular, speeds increased and very soon woven asbestos displaced belting, in order to deal with the greater heat created by the higher speeds.
The 1914/18 war with its enormous consumption of vehicles of all kinds and the introduction of the tank in warfare for the first time produced an even greater demand. From the little hut, and through the foresight of one man, Herbert Frood, has grown the great modern Ferodo works of today.
Manufacturers: Ferodo, Ltd., Chapel-en-le-Frith, Stockport.
Over more recent years Girling have fitted various prototype disc brakes to a number of racing and sports cars. Among these were the original 1½-litre supercharged B.R.M., Aston Martin, Cooper, Lotus Lister, Connaught and others.
There were a number of snags, however, particularly in the early days, as far as the length of life of the lining was concerned. The early disc brakes had a caliper set astride the disc which housed three pairs of circular friction pads. Wear of these pads was very high under racing conditions and they had to be renewed at frequent intervals.
A vast deal of extremely valuable experience was gained by the Girling Company through its experimental work and by fitting its disc brakes to sports and racing cars. At the same time the cars so fitted achieved a braking, performance of a very high standard. One has only to think of the 1954 Le Mans Race where the Aston Martins astonished everybody by their ability to brake at the last moment, this being the first occasion on which the segmental type disc brake was used in this race.
Currently Girling disc brakes are fitted to a number of British sports and racing cars, and in addition to the works Aston Martin team of DB3Ss, the Lotus's, which are unusual in that the rear disc brakes are inboard in consequence of the de Dion rear axle, the new Formula II Lister Climax and the new Formula II Cooper Climax; it was recently announced that all future TR3 models also will have Girling disc brakes on the front wheels.
Although the basic principles of the early versions of the brake have been retained, current units incorporate some important detail changes with a consequent enhancement of performance.
The small circular friction pads originally used have been replaced by segmental ones of substantial thickness. The segmental form of pad is ideal for the disc type of brake since the braking effort is distributed uniformly across the working face of the disc. If this uniformity is not provided, concave wear of the braking path occurs. These segmental friction pads are bonded on to steel plates and are pressed against the disc by the pistons of two hydraulic cylinders, one behind each pad, acting at the effective centre of the pads. The cylinders are connected by a bridge pipe so that the pressure on the sides of the disc is at all times equal.
The caliper in which the friction pads and their actuating cylinders are mounted is open at the centre. This enables wear of the friction pads to be checked at a glance, so that wear indicators of any kind are quite unnecessary.
When the time arrives for replacement, the pads may readily be removed by loosening the set screws which hold the retaining plates.
The Girling range of mechanical and hydraulic brakes for normal production cars still continues.
Manufacturers: Girling, Ltd., Kings Road, Tyseley, Birmingham 11.
A subsidiary of Automotive Products of Leamington Spa, Lockheeds are famous producers of braking systems. Their present range includes standard and power-operated hydraulic brake systems, vacuum-servo, disc and transmission brakes.
In the vacuum-servo range two new units have recently been introduced. Suitable for the faster heavy car these are of similar design to former units, but differ in the diameter of the vacuum chamber and consequently in the power available. The transmission brake has come into its own once again especially with the advent of disc-brakes since the high leverage of this mechanism means that the hand brake must frequently be adjusted. In the Lockheed design a drum is used, but instead of containing a pair of brake shoes the drum is machined inside and outside and is pinched between a pair of pads which are operated by a simple link mechanism.
The new Lockheed disc brakes for production cars are suitable for the front and rear wheels of large high performance cars.
Manufacturers: Lockheed Hydraulic Brake Co., Ltd., Tachbrook Road, Leamington Spa, Warwicks.
An internationally known name linked with brake and Clutch liners. The origin of this firm, now known as British Belting and Asbestos, Ltd., can be traced back to a chance meeting between an Englishman and a Scotsman in Sweden during the year 1878. The Scotsman, William Fenton, and the Englishman, W. Willson Cobbett, went into partnership in 1882 to make woven textile machinery belts in Dundee, the centre of the jute industry. The new type of belt was given the name "Scandinavia" and in 1908 the firm succeeded in obtaining orders for the Rolls-Royce cone clutches and later transmission band linings for all the Ford Model Ts, the firm had made its name and changed its title to "Scandinavia Belting, Ltd."
A great variety of other products are made by this same firm, but these are too numerous to mention as are the many different types of brake and clutch linings. Considerable time and money is spent by the company in testing all these products and the Mintex International Racing Service is but one of many aspects of research. The familiar yellow vans are to be seen at most race meetings throughout the season in this country and abroad ready to give information and assistance on matters concerning brakes and clutches and to follow the progress of those linings already in service.
Manufacturers: British Belting and Asbestos, Ltd., Cleckheaton, Yorks.
Manufacturers of clutch and brake linings for all types of vehicles from light cars to heavy commercials, the Raybestos-Belaco Company has considerable experience in all the applications of these friction materials.
Manufacturers: Raybestos-Belaco, Ltd., Everith House, Southwark Street, London, S.E.1.
Small & Parkes
Small & Parkes of Manchester began to make brake and clutch linings in 1913. This family concern (founded in 1881) started by making steam engine packing (Karmal) and transmission belting (Roko) both of which are still widely sold -- but the present-day accent is on the production of Don brake linings and Donflex clutch discs. Since 1913 the manufacture of Don brake linings and Donflex clutch discs. Since 1913 the manufacture of automotive friction materials has expanded immeasurably and the company's plant has grown to keep pace with the production demand (for example, a completely new factory for moulded brake linings was erected at the Hendham Vale Works in 1950 and extensions are concurrently being made).
The importance of research has not been overlooked, and the Research and Development Department has been built up steadily, especially in recent years; a new laboratory building is just being completed, and there are plans for even further extension. The road-testing section is especially important, and the new laboratory includes a road-test garage fully equipped to work on the brakes and clutches of all types of private and commercial vehicles. The present test fleet covers a wide range of cars, from the Ford Anglia and Standard Vanguard to the Jaguar XK140 and Lancia Gran Turismo. These vehicles, instrumented to measure the various aspects of brake and liner performance, are run to carefully planned programmes of bedding-in, engineered tests and performance running, involving thousands of miles. Such programmes are necessary, of course, to provide the final answer in the development of automotive friction materials. Prior to World War II, the Company were interested in competition work but, in post-war years, have confined that interest to rallies and have not adopted a policy of sponsoring individuals.
Recently Motor Sport had a set of Don R14 brake linings fitted to a Jowett Jupiter. These linings are primarily intended for cars on general work and not for competition use. Tests were carried out before and after relining, the main differences being in the feel of operation of the brakes which were more progressive and smooth in action, although a slightly heavier pedal pressure was required to achieve a full g. stop on a decelerometer than was necessary with the previous linings. This quality, Don R14, is one which has recently been introduced, it is a moulded lining intended for light and medium passenger cars and light sports cars, and we found it entirely satisfactory for use in the Jupiter.
Small & Parkes made an extensive range of brake and clutch linings, both woven and moulded. In general, the Technical Department likes to recommend qualities to suit the customer as well as the car -- whenever this is possible. The moulded brake lining range varies from rolled types (such as Don R1, R3 and R14 -- general-purpose car liners) to heat-and-pressure moulded types (such as Don 24, ML2 and Don 424 -- for high-speed motoring and heavier vehicles). Don 424 is a variety which has been markedly successful in competition work, racing and rallies. The range of woven brake linings includes Don BS5, which has been well known for many years for high performance and good wearing characteristics.
Manufacturers: Small & Parkes, Ltd., Hendham Vale Works, Manchester, 9.