MOTOR WORLD

Hawera Star, Volume XLVI, 18 September 1926, Page 14

MOTOR WORLD

FOUR-WHEEL BRAKES.

INTERESTING SYSTEMS,

There arc many interesting features incorporated in the four-wheel braking systems of the ears of to-day, to which reference was made in a previous article, and one of the most interesting is the Dcwandre, a Belgian invention, which is fitted to several of the highest class Continental cars, while it- is also -manufactured under license m This system works by a vacuum process, and is so effective that it is claimed to have brought, a ear weighing tons to a complete stop from a speed of 40 miles an hour m less than dU yards. The brake'pedal is connected through a svstem of rods and levers with the brake operating arms, mud this ensures that even if the vaca Y_ servo system broke down the brakes would still be effective,“as their application could be continued mechanically. The vacuum system is operated by a suction pipe from the induction manifold to the servo, which exhausts the air in a cylinder and draws forward a piston attached by a chain to the break-operating rods. When the brake pedal is depressed i/t causes the suction to act on the piston, which comes into action and assists the pressure exerted by the driver J s foot on the bfakes. _ Reference was also made to the interesting : hydraulic system adopted by the Studebaker corporatio. This brake consists of a transmission case containing the piston chamber and pistons, control valves, and relief valve of the braking 'system, and it is kept threefourths filled with' transmission oil, which serves the double purpose of lubrication and hydraulic fluid. A pump operated by the propellor _ shaft keeps the oil in'constant circulation from the bottom of the case through a passage underneath the piston chamber into the pump and back again through the control valv<3 passage. When tho brake pedal is depressed it closes the control valve and the oil is forced into the chamber between the heads of the pistons, -which move outwards and apply the brakc-s. Upon removal of the foot from the brake pedal the control valve re-opens, oil •circulation is restored, and the brakes are released, the pistons returning to their drawn by two springs. When the maximum pressure at which the brake operates is reached, as .shown jby a gauge on the dashboard, the relief valve opens and allows a portion of the oil to circulate through the transmission case, and thus prevents excessive brake pressure. This is a safeguard to prevent the back wheels being/locked for more than a very short period, and reduces the liability to damage through too fierce application of the brakes. It is further provided that this maximum pressure of the hydraulic brake occurs when the brake pedal has been depressed to half its possible distance; continuing the pressure beyond that distance mechanically applies the rear wheel brakes, which will also lock the back wheels until the pressure of the pedal is released. ' .As the pump will not generate pressure when running in reverse, the-brake rods are so arranged that tho four,/wheel brakes are operated by foot pressure. The only adjustments necessary on this system are tightening or adjusting the bands on the rear wheels. Lubrication is necessary on accessible friction points'of the system. The Lockhead system, which seems to be 'incorporated in more makes of ears than any other hydraulic, has a master cylinder mounted horizontally on the left-hand side of the transmission case. The brake pedal depresses a piston in this cylinder, and forces a mixture of castor oil and methylated spirit through copper tubes into the brake-operating cylinders on the wheels. Opposed .pistons in these cylinders operate the brake bands. This system automatically equalises the pressure applied to each wheel, and is incorporated in about ten different makes of American and British c'ars on sale in Sydney., Brake linings to-day are undoubtedly considerably better than were those of 18 or 20 years ago, the adoption of asbestos, bonded with brass or copper wire, having been most successful. Even at that, however, adjustments are occasionally necessary, while sooner or later it becomes vital to have the brake relined. Many systems to-day incorporate remarkably simple and easy means of readjustment of. the brakes with compensating devices to eliminate ithe danger of unequal adjustments as much as possible, aiid some of the best cars are so designed that the whole four brakes can be tightened or loosened by screwing one wing nut. Relining the brake shoes is also made as easy as possible, but is nevertheless a task which takes a few hours and needs care to ensiire that the new lining fits smoothly, tightly, and firmly around the whole friction* surface of the shoe.