It is obvious, however, that the power exerted through either type of brake, depends on the leverage afforded by the relative lengths of the limbs of the bell-crank lever E, to each other. CONTRACTING BRAKE.--Fig. 25 shows a well-known type of contraction brake, in which the cylinder A, has thereon two brake bands B C, hinged together at their rear ends. At their front ends they are connected with a bell-crank lever D, the forward movement of the upper end of the lever being such as to cause the bands to pinch the drum A. A contractile spring E draws back the lever when the foot releases the pedal, and the link F, between the bell-crank lever and the upper band C, has a turnbuckle arrangement to provide for taking up in case of wear. The brake bands have means for automatically holding them clear of the wheels when not in use. [Illustration: Fig. 25. Contract Mechanism.] EQUALIZERS.--Sometimes the brake is placed on the propeller shaft; but when one of the brakes is placed on each wheel, an equalizing bar, or other means, must be used. One form of this is shown in Fig. 26, in which A is the bar, B the rod which goes to the brake lever, and C C, the rods that run back to the brakes on the wheels. Naturally, the equalizer will not act with the same effect on both wheels, unless they are in the same condition. Frequently one of the brake cylinders will be dry and the other coated with grease, or accumulate moisture from some source. It is, therefore, a necessary part of inspection and care to keep them in serviceable condition. [Illustration: Fig. 26. Equalizer Bar.] THE EMERGENCY BRAKE.--The emergency brake has a pawl which acts in the teeth of a segment alongside of the lever, so it may be held in any position to which the lever may be thrown. This lever has no provision whereby the clutch is disengaged when the brake is applied, for the reason that should it become necessary to stop a car going up hill, and when the emergency brake is required, the brakes would have to be released before the clutch could be thrown in, so that the car would be likely to start down hill before this could be done. On this account the emergency brake has no connection with the clutch. [Illustration: Fig. 27. Rear axle. Service and Emergency Brake.] COMBINED SERVICE AND EMERGENCY BRAKE.--Fig. 27 represents a standard type of service and emergency brake, each of the internal expanding type. As both are inclosed in a drum they are absolutely free from dirt and dust, and the construction shown eliminates rattling of the parts. The wheel bearing is also represented by the annular ball-bearing type of construction, in which the balls are unusually large, and therefore, capable of taking great weight and high speed without undue wear. CHAPTER V THE DIFFERENTIAL