S-cam brake units from Moss Gears
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• The Moss Gear Co. Ltd., which in June last year introduced a new range of semitrailer axles, has now announced that the S-cam brake unit which was designed for the axles is to be marketed as an individual item.
The units are produced in diameters of 12.5 in. and 16.5 in., the smaller size being available in widths of 4 in., 5 in., 6 in., and 7 in. and the larger in widths of 5 in., 6 in., 7 in., and 8.625 in.
Fabricated shoes are used and these carry tapered liners to give good wearing properties. Cam rollers are retained in the shoes by spring-clips and the camshafts are one-piece forgings. Torque capacities of the camshafts are, for the 12.5 in. units, 5,800, 6,550, 7,520 and 8,850 lb.in. respectively and for the 16.5 in. units, 9,175, 10,580, 13,200 lb.in. respectively. The drum retardation torque figures obtainable from the units range from 53,000 to 138,000 lb.in.
Two common spider-brackets are used in the ranges, both being forged to allow boring for 4.5 or 5 in. diameter axle-tubes. The heel ends of the shoes are carried on large diameter, hardened-steel pins which in turn are carried in an Oilite bush in the bore of the spider. The pins are secured by split pins and washers at each side, and shoe return is by two short coil-springs arranged in tandem and joined by a short linking rod. The cams are designed to provide constant lift characteristics at all points of their profile.
The camshafts are carried in nylon bushes, the inboard one of which has a spherical moulding on its outside to facilitate accurate alignment. The bushes are provided with grease nipples and are equipped with 0-ring seals.