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Q. Discuss features of internal brake location.

A. An important advantage of the internal brake is that it is entirely enclosed and protected and that it can be firmly attached to the member taking the braking torque. As it is installed inside of the brake-drum it is liable to be affected by accumulations of lubricant leaking out from the axle housing. It is also difficult of access for repairs or adjustment, so most designers endeavor to provide a construction that will not need frequent adjustment, and then use this brake for emergency purposes so that it is not called

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Fig. 262.—Typical Propeller Shaft Brake of External Constricting

Band Form.

on as often as the regular service brake which is usually of the external band pattern.

Q. Discuss disadvantages and advantages of external brakes.

A. Most of the external brakes have a disadvantage in that they are apt to rattle against the brake drums and also that they detract from the neat appearance of the wheel owing to their unsymmetrical form. Brakes of this nature are very efficient, however, and they may be easily adjusted or removed if it is desired to replace the brake lining without disturbing the wheel, as would be necessary if the internal brakes demanded attention.

Q. What materials are usually employed in brake construction?

A. Materials to be used in brake construction must have strength, endurance, and possess a high degree of friction. The materials ordinarily used are metals where strength is desired and various fibrous substances having a high degree of frictional adhesion for brake linings and facings.

Q. What are brake drums made of?

A. Brake drums are commonly made of steel, those on the lighter cars are formed by stamping the drums from the sheet under powerful presses while on heavy vehicles steel castings are employed. With the ordinary form of pressed steel brake drum the surfaces are sufficiently smooth and true to size so no machining is necessary, but the castings must be faced off in order to obtain a smooth surface against which the brake band can bear.

Q. What are brake shoes made of?

A. Brake shoes may be made of steel, bronze, or malleable iron castings on the larger types and of drop forgings in the smaller sizes.

Q. What materials are used to increase friction of brakes?

A. Among the materials used to promote greater frictional adhesion may be mentioned camels' hair belting, woven wire and asbestos fabrics sold under the trade names of Raybestos, Multibestos, etc., and cork.

Q. How is brake lining attached to band or shoe?

A. Brake linings are attached to the brake bands or shoes by means of copper rivets which are countersunk in the friction material and tightly riveted over at the inner side of the brake band.

Q. How are cork inserts used?

A. Cork is employed in the form of inserts which is compressed into suitable holes drilled to receive them in the brake shoe castings which are generally of bronze or cast malleable iron when the

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Fig. 263.—Countershaft Brake of the Caliper Type Used on Packard Motor Trucks.

cork is employed and of special form having pockets to receive the frictional material. The use of cork provides for a greater degree of friction and enables the brake to work more efficiently if oil is present between the surfaces and also promotes gradual brake application.

Q. What must a brake do to be efficient?

A. In order to have the vehicle under perfect control a brake must be able to lock the driving wheels in a manner that will entirely prevent them from rotating, and it should be capable of performing this function with minimum exertion on the part of the operator.

Q. Are quick acting brakes desirable?

A. Quick 'acting brakes, which will stop the wheel rotation too soon, are not desirable because these make for rapid tire depreciation. Most brakes are designed so they can be applied gradually.

Q. How are brakes operated ? A. The service brakes, which are generally of the external form, re operated by a pedal adjacent to the clutch pedal, while the emergency brakes, which are usually of the internal type, are brought into action by a hand lever mounted near the gearshift member and carried on a quadrant and provided with a latch so that it can be locked in position.

Q. What is a clutch and brake interlock?

A. In some cars a single pedal is used to control both clutching and braking functions. The pedal is only pushed about half way of its available travel to release the clutch quickly and from that point to the end of its movement it will apply the service brakes. Obviously, it is not possible to apply the brake without first releasing the clutch. In some other forms of cars the brake pedal is connected with a mechanical leverage so that it cannot be moved without throwing out the clutch, though the clutch pedal may be moved without applying the brake. The clutch and brake interlock is sometimes obtained by the emergency brake lever and this construction is preferred to the foot brake and clutch interlock.

LESSON TWENTY-NINE

GENERAL DRIVING INSTRUCTIONS

Q. What is the general road rule of this country?

A. When approaching a vehicle coming from the opposite direction the rule is to keep to the right of the road and to pass all vehicles going in the same direction on the left.

Q. How does this differ from the road rule of Europe?

A. The road rules of most of the European countries are just the reverse to those in vogue in America as the vehicle must keep to the left of the road and pass conveyances going in the same direction on the right.

Q. What is the logical position for steering wheel and control levers, and why?

A. In order to conform to the road rules of this country the logical position of the steering wheel is at the left side of the car and the control levers should either be at the extreme left or in the center of the car.

Q. Why is right hand drive so general in this country?

A. As most of the American automobiles have been derived and adapted from European designs the right hand location of the steering wheel has been preserved with other features and while this is logical for the road rules obtaining in foreign countries it is not so well adapted to American conditions as the left hand drive.

Q. Why is central location of control levers desirable when steering wheel is placed on left hand side?

A. As most motorists are familiar with cars in which the speed changing is performed with the right hand and as most people use their right hand to better advantage than the left, placing the control levers at the center of the car enables one to handle the steering

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