Document mqqkjoE11rqymL813p3MDMLwJ

31 ing braking to reduce high localized pressures on portions of the lining, which otherwise may lead to heat check ing and scoring of drums, out-of-roundness of drums, and charring of the brake lining. Minimization of these ill effects lead to longer lining and drum life, it is said. Description and Applications of FR2 Brakes The plain FR2, without following letter, is generally applied to medium weight trucks, while the FR2S and the FR2SD are used in the heavy-duty truck field; the "2S" being primarily used for the front axle, with the "2SD" in the rear. The basic appearance of all FR2's is similar. The FR2 and the FR2S each have two identical shoes and two iden tical wheel cylinders. The main differ ence between these two types is that the plain "2" uses a backing plate, while the "2S" is mounted on a spider. The "2SD" is a dual-type brake with four shoes. The latter, in appearance, is com parable to two "2S's" placed back to back. It employs two Siamese-twin-type wheel cylinders to actuate the dual shoes. The shoes on all the "2" brakes are arranged with their toes opposite each other on the brake diameter, and the double-end wheel cylinders are placed between the toe of one shoe and the heel of the other. An equal amount of hydraulic pressure is thus applied at each end of each shoe. All shoes are forward-acting, independently actuated in the direction of rotation of the wheel. All shoes anchor at either the toe or heel, depending upon the direc tion of rotation of the wheel and its drum. Each anchor and adjusting sup port carries a removable anchor pin at the heel end of the shoe; there is a star wheel and adjusting screw at the toe end of the shoe. The shoes on all "2" brakes are the floating type. Each shoe is held in posi tion by a shoe guide pin, washer, shoe guide spring "C" clip, and two shoe re tracting springs. In regard to differences in shoe retracting springs, the plain "2" springs are all the same; however, on the "2S" and the "2SD," the heel-end spring is short, and the toe-end spring, long. Adjustment of FR2 Type Brake To adjust the plain FR2 type brake, remove adjustment slot covers and in sert wrench or screw driver into slot to contact star wheel. Rotate star wheel toward axle, using outer edge of slot as fulcrum for the tool. Decrease clear ance between shoe and drum in this manner until shoe drags. Then, turn star wheel "three clicks" in the reverse direction to provide correct clearance. This procedure is repeated, of course, on each of the shoes. Replace adjust ment slot covers. Adjustment of FR2S and FR2SD Type Brakes Adjustment of these types is similar to the FR2 except that there is an adjusting worm instead of a star wheel. Insert Ys in. hex-head wrench through adjusting hole in dust shield enclosure to fit firmly in adjusting worm. Rotate wrench in forward direction of wheel rotation to decrease clearance, until wheel drags. Then, reverse direction of turning wrench until drag is relieved. Now, rotate wrench one additional turn to provide correct working clearance. On the 2SD, the dual shoes may be adjusted individually or simultaneously. Miscellaneous Adjustment Tips Make all adjustments with the brake drums at normal temperature, and see that the wheel bearings are correctly adjusted. Manually-operated and vacuum-hydraulic-actuated brakes require adjust-