Arresting development
Early motorists coping with rear-only brakes feared “the dreaded sideslip”. Bill Boddy follows the development of four-wheel braking
Brakes on modem-day cars,whether drum, disc/drum or all-disc, some with the reassuring presence of ABS, tend to be given little thought, but their development was a long and often complicated engineering study.
Early cars were not badly anchored, transmission or rear-axle drums taming the faster and heavier ones, but this put a strain on driving-chains and propshafts. Driven were timid of the ‘dreaded sideslip’, when locked back wheels had the dumb-bell effect of setting up skids. It must have been clear to Englishman F L Renouf that having brakes on all four wheels would not only decrease pulling-up distances but would cure unwanted sliding. That was in 1903.
British car-makers who heeded this were Argyll in Scotland and Crossley in Manchester, who before WWI had four-wheel brakes on production cars, the former coupling them diagonally, as did Excelsior after WWI. But they were before their time, abandoning such brakes for some years on their wartime and post-war cars. M. Perrot had worked with Argyll before taking his ideas to Europe, where Isotta-Fraschini had 4WBs on its great 100hp chassis before the war, and a few other makes had followed the Argyll lead.
If the racing car of the day was the touring car of tomorrow, lessons should have been learned from it. The great Georges Boillot apparently tried the Argyll racer at Brooklands and convinced Peugeot’s racing-car designer Ernest Henry that the front wheels of the car with which he was favourite for the coming great 1914 French GP must be given brakes. For this monumental contest Delage, Fiat and Piccard-Pictet also had 4WBs. They may have given extra pace into the comers, but the rear-wheel-braked Mercedes outran them, to a 1-2-3 victory. Moreover, it was some time before the lessons from Jimmy Murphy’s win in the 1921 French GP with the ‘water-braked’ Duesenberg, fluid taken to its front wheels though the hollow front axle, were commercially heeded.
But at the 1919 Paris Salon and Olympia Show, the 37.2hp Hispano Suiza was a sensation, not least on account of its servo 4WB brakes. The effort of taming this fine fast car was achieved with a Sin drum with an expanding-shoe servo driven at 1/64th engine speed by helical gears from the gearbox and coupled to the cables. These operated the shoes in the all-wheels 15 1/2in diameter finned, steel-lined aluminium brake drums. The handbrake applied the back brakes only, for parking, but if either system failed, the other remained operable. This servo assistance was appreciated not only by macho males, but by lady motorists with slim ankles.
Delage, on its splendid new 40/50hp chassis, had well tested mechanical servo braking similar to that of Birkigt’s Hispano. Other top-quality cars had to follow, and it wasn’t long before Sunbeam, and Renault for subduing its 9-litre 45hp monster, had servo braking, the latter using a contracting band in place of shoes. This put Rolls-Royce in contention. They must likewise have better brakes, as their Silver Ghost still had only 2WBs ;but foolproof performance was essential. The Derby company was therefore willing to pay royalties to both Hispano-Suiza and Renault to perfect its system, which used a gearbox-driven disc servo and a complicated compensating linkage, which did not appear until 1924/25. It worked impeccably, except for a tendency for the Royce to roll a few feet before finally stopping. The R-R mechanical servo, with later improvements, did not die until replaced in 1965 by hydraulically actuated all-round discs on the Silver Shadow and T-model Bentley.
After the 1914-18 war the majority of cars still had only rear-wheel brakes. But the industry was joked in 1922 when Sir Herbert Austin announced his Austin 7, with 4WBs. The drums may have been minute, retardation minimal, the cables stretchy, but nevertheless… The pedal put on the back brakes, the hand lever the front ones, logical if you think about it, because normal slowing was usually done by pedal. It wasn’t until July 1930 that the Seven’s pedal applied all four brakes.
By about 1924 no respectable manufactures could evade 4WBs. But what a strain this must have been to deputy-engineers and head-draughtsmen, when simple cable linkages, as accepted by Lancia, were so often eschewed for complex compensated layouts. A few designers, remembering that their cars had differentials at the back, felt that on corners the inner front wheel should be braked less than the outer one, an additional problem to solve! Some drivers were at first fearful of the new FWB systems, saying that to brake the wheels that steered might put them in the ditch or worse, if these locked-up.
New problems thus arose: how to compensate and provide adjustment for four brakes, and should front-rear action be 40:60, 50:50, or what? How did you cope with braking wheels that turned, without loss of full retardation? This is evident in a description of the layout adopted by the Herbert Engineering Co. of Caversham in 1925, for its attractive HE cars: “The front-wheel brakes have been improved and simplified; the rear-wheel drums contain two separate sets of shoes, one of which is operated by hand, thus providing a six-wheel system — previously the lever only exerted extra pressure on the same set of rear shoes. In the HE design the shoes are forced apart by a rectangular-shaped cam on a spindle which, passing through the backplate, carries a helically-geared wheel, engaging with a similar wheel in such a way that the latter takes up a backwards and forwards rotation. The spindle is splined and its forward end takes a short arm, at the lower end of which is formed a spherical socket. Into this fits a half-ball, to which is attached a small pulley, round which passes the brake-operating cable. The latter then passes round a pulley attached to the frame, and then back to the adjustment at the side of the chassis.”
Read again, and note the word ‘simplified’! If asked to design such a system wouldn’t you have looked for a new job? The HE had adjustments for the front brakes, for all four, and for the brake pedal, and a refinement was a handwheel, for the driver to adjust the front/rear braking proportion while the car was in motion, also used by A C Bertelli on the Aston Martin and on a few other cars, including the racing Bentleys.
All manner of complication was the norm at first, cast-iron or brass shoes persisted, until fabric linings quelled their injured shrieks when applied. Ferodo was a popular brake lining, advertised with the name in big letters on bridges spanning dangerous bends.
The Perrot front-brake layout was perhaps the best, with the operating spindles supported on the chassis (or on the axle on Daimlers) and on the drum backplate, with a universal joint incorporated. W Bentley went for it, as had 36 others by 1925 including Delage, La Buire and Mercedes. Voisin obviated u/js by putting the operating rod down the steering-pivot Hotchkiss and Windsor also had the Perrot rods on the axles, with different u/j arrangements. Panhard expanded the brake shoes by rack-and-pinion, the SLIM had the cam-lever above the drum, FN above the steering-pivot, with wedges to operate the shoes, while SPA used threaded sleeves on the axle. Rolland-Pilain had oil pumps on front and back axles working pistons coupled to the brakes while Fiat used two servo oil pumps in the gearbox on its V12 and 40hp models. De Dion had neat geared compensators and Crossley used U-levers for the front brakes, mounted on the axle by the swivel-posts.
Had the lesson of the racing Duesenbergs been heeded all this could have been avoided, because hydraulics give direct compensation for each wheel automatically. Chrysler led with this in the United States, followed by Triumph with Lockheed, and Horstman here, but in GP racing it wasn’t until Mercedes-Benz had independent suspension in 1935 that it found the flexible hydraulic brake-system to be an advantage.
The 1920 GP Ballots had the Birkigt/Hispano servo under licence, but driver Ralph de Palma disliked it and had it disconnected. The 1922 TT Vauxhalls used a compressed-air servo, the 1922 GP Fiats an oil-servo, the 1924 GP Sunbeams a disc servo and complex cable and pulley compensation, the 1927 Delage cars a shoe servo and an ingenious chain-and-sprocket front linkage designed to obviate locking of the front wheels, and the P3 Alfa Romeo had bellcranks to rods in the kingpins, and no servo.
As 4WBs became more and more popular, only the Model T Ford and the Trojan ignored them, while Jowett and Chevrolet took their time. Alford & Alder, until bought by Morris, and Whitehead offered proprietary 4WB sets. By 1923 32% of cars on the British market had 4WBs, by 1924 it was 47% plus 6% optional, and by 1925 it had reversed, to 75/25%. In 1932,28 chassis had four-drum eight-shoe brakes, 15 used four drums with 12 shoes, and 15 still had a transmission brake, 12 having this applied by hand-lever. Linkage was by rod on 31 makes, 18 used cables, six a combination of both, and Amilcar, Ansaldo, La Buire and Voisin opted for steel tapes. Chenard et Walcker and Bignan braked only the front wheels, via a Hallot servo. Early Bugattis and later Rileys relied on a single cable but then on a Bugatti ‘you braked with the horn’. The Riley continuous cable system levers and pulleys The Autocar described as difficult for the lay mind to understand and almost impossible to describe!
Inexpensive US cars sometimes had external-contracting brakes, which might succumb to rain, although I recall being very impressed with the power of those on a circa-1924 Buick. Vacuum servos were a substitute for mechanical ones, which Parry Thomas had on the fabulous 2WB Leyland 8 by 1920 and which Dewandre later popularised for cars and commercial vehicles.
Rolls-Royce grandiloquently referred to its Six-Brake System’, which got a speeding charge dismissed when the top motorists’ banister told the magistrate of it, but others also had six brakes, i.e. four pedal ones and two more for the separate handbrake. In its roadtest reports The Autocar quoted stopping distances from 30mph, the lower open road limit; however, Autocar now quotes in seconds, which I find less meaningful. Best 30-0mph distance back in 1930, out of 69 cars tested, was 25ft, by a 4 1/2-litre supercharged Bentley.
Now hydraulic brakes are universal and generally foolproof. But let’s not forget the 1955 Citroën DS19’s pressure brakes, or that anti-locking was pioneered by Dunlop-Maxaret on the memorable four-wheel-drive Jensen FF of 1966 to ’71, and discs by Dunlop/Jaguar if we can overlook AC’s feeble rear-axle single disc.