Class 8 Mack Straight Emulating a Refuse Hauler: Braking Improvement Study

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Class 8 Mack Straight Emulating a Refuse Hauler: Braking Improvement Study

R. L. Hoover / T. R. Van Buskirk / W. R. Garrott

The effect of higher output foundation brakes were determined for a Class 8, Mack 6x4 MR-688-S straight truck which emulated a McNeilus refuse hauler. Four brake types studied included: original hybrid S-cam drums, big S-cam drums, hybrid disc, and all-disc. In order to simulate the completed refuse hauler, the mock-up truck was loaded in three configurations: fully laden at GVWR, at LLVW simulating an unloaded refuse hauler, and empty (MT) for comparison to other chassis-cab test trucks. The results show that the chassis-cab mock-up truck with hybrid S-cam brakes produced performance data similar to that obtained from the McNeilus refuse hauler for most tests, which indicated that the mock-up was realistic in loading configuration and in braking capability. At GVWR, the test truck stopped in 298 feet, which correlated to the 302 feet obtained by the refuse hauler. By installing higher output brakes, the service brake stopping distances shortened dramatically. The all-disc brakes performed the best (228 feet), followed closely by the hybrid disc brakes (245 feet) and the big S-cam drum brakes (248 feet). For baseline brake-in-a-curve (BIC) tests, all four brake configurations met the minimum stability and control test requirement; therefore, increasing the brake output made little change in stability on the low-coefficient-of-friction surface. Additional loads of GVWR and MT produced similar results at the 75-percent of drive-through target speed for four-of-four tests. For limit-speed tests, the highest lateral acceleration performance quotient (LAPQ) values were achieved by the hybrid S-cam and big S-cam brake configurations.