HYDRAULIC BRAKES

Wanganui Chronicle, Volume 79, Issue 123, 26 May 1936, Page 5

HYDRAULIC BRAKES

A 1936 Feature , A pronounced feature of the New 1 York Automobile »Show vias the fact mat a great number of manufacturers have adopted’hydraulic brakes, indicating by this consensus of opinion that ‘ hydraulic braking systems, correctly engineered, are the most reliable and safest braking system available for ' motor vehicles, states General Motors Automobile Association. The reasons | assigned for this change are simplicity l q of design, case of operation, and safety and reliability in operatiou. While most motorists recognise '■ hydraulic brakes as an ideal system, . mey have no appreciation of what con- ’ statutes this feature. In a hydraulic braking system, the operation of the brake shoes, expanding tu contact with d the brake drum which is revolving on the wheel, cause the friction wnich 1 brings tiie car to a stop just as in the case of mechanical braxes. The differences between the two systems and the ' advantages of hydiaulic brakes are ia what is known as the actuation of the system, that is, the method of applying me force exerted on the foot pedal to the brake shoes at the wheels. The shoes are brought into contact e with the drums by means of a column of liquid forced through pipvs. This liquid, being incompressible, transmits 51 pressure applied by the foot pedal to s each wheel brake shoe by means of displacement of pistons in master and wheel cylinders. Inasmuch as the pressure must be equal in all parts of the system, no braking action can take place until all the shoes are in contact with the drums, therefore the system is self-equalising insofar as brake shoe pressure is concerned. } The system consists of a master c cylinder in which hydraulic pressure is j built up by the brake pedal with tubing ] running to each wheel cylinder, which r is positioned between the two brake f shoes in each wheel. The master f

cylinder is fitted with a piston and has a reserve reservoir which maintains a constant volume of liquid in the tubing and wheel cylinders which have two pistons. Rubber cups are fitted in all uf the cylinders to maintain pressure and prevent loss of fluid. When the brake pedal is depressed, it moves the piston within the master cylinder. The pressure thus created is transmitted to the wheel cylinders causing pistons to expand brake shoes against the drums. As the pressure on J the pedal is increased, gieatcr hydraulic pres ure is built up in the wheel cylinders and consequently greater force is exerted against the drums by the brake shoes. When the pressure on the foot pedal is released, the springs on the brake shoos return the wheel cylinder pistons to their normal or “offposition, tons forcing lhe brake fluid back through the tubing into the master cylinder. A springloaded check valve located in the end of the master cy.inder maintains a constant pressuie in the tubes and wheel cylinders of approximately si’< | pounds. The construction most favourable seem to be mat in which the wheel cylinders are fastened rigidly to the braking plates instead of one of the shoes, two pistons beong used in each wheel cylinders. This construction al’.cws both shoes to be removed for relining', whenever necessary, without removing the wheel cylinder. It also permits a more positive return spring arrangement, and : assures quiet operation ct’ the brake shoes.