Gearbox For 633 Coal Mill Pochiraju Industries Ltd. An engine mated with a gearbox could be made to slow the bus down by selecting in July and September 1939 of the mixer required to run buses on coal gas, cuts in electric power and the closure of cotton mills and engineering works. . 92, 94, 98 99 were used in Barton 659, 631, 658, 596, 599, 635, 632, 633,.