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An Articulated Four-shoe Brake.

25th January 1927
Page 66
Page 66, 25th January 1927 — An Articulated Four-shoe Brake.
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ANINTERESTING type of internalexpanding brake is being marketed by Zenith Brakes, 14, Auburn Road, Bristol.

The ordinary two-shoe brake. as is well known, possesses some really serious defects. By employing a single pivot and expanding the shoes by means of a cam at one side only unequal pressure and wear on the friction material are bound to occur. Consequently the material has to be renewed far more frequently than should be necessary, and the method does not permit full advantage being taken of all the braking area.

In the accompanying diagrams of the Zenith duplex brake it will be noted that not only are four shoes employed for both the foot brake and the side brake, but that in each case the four shoes are articulated at four points, providing much greater flexibility and enabling contact to be made over a greater surface of the friction material and of the drum, which, apart from promoting economy and efficiency, assists in preventing that distortion which is so liable to occur in any other than a very heavy and rigid drum; but a more novel point still in the Zenith brake is that the cams are duplicated and act diametrically opposite each other, so giving uniform expansion.

We would draw the attention of readers to the upper and lower pivots on which the shoes are suspended, as these pivots relieve the brake-operating mechanism of all torsional stress, a feature of great importance.

The principle of the operating mechanism is that four or more eccentric cams, formed solid with the brake shaft, engage with renewable sliding

blocks pressing against the shoes, thus providing a full bearing surface on the abutment end of each brake shoe at any particular point ' of leverage. The action is a wedging one and provides a powerful expanding force.

Adjustments are provided for the wearing faces of the shoes and also for inequalities when fitting, whilst external adjustment is arranged for on the two operating levers.

It is claimed that this brake gives equal efficiency in either direction of travel and it would certainly appear to be a great improvement upon the ordinary single cam of lozenge pattern.

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People: Zenith Brakes
Locations: Bristol

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