New Gearboxes from David Brown
Page 42
If you've noticed an error in this article please click here to report it so we can fix it.
THREE new constant-mesh gearboxes
are now being offered by The David Brown Corporation (Sales) Ltd. Following a revised policy by the concern, the new units have type numbers which denote the maximum torque input for which they are designed, as well as the number of ratios provided. The boxes are the 285, 360 and 650, the ratio figure being added in front of the particular type number, and each is available in alternative forms.
The 285 is similar but a little larger than the recently introduced 260 (used by Seddon as the 5.260 in the new 13:Four) and, like this box, is available as a five-speed with overdrive or direct top as the 5-280, as a six-speed overdrive —the 6-285—or as a 10-speed overdrivetop unit—the TR 5-285. As with the 260, on the six-speed overdrive model the additional gearing is contained in an added section at the rear of the casing. The 10-speed has a splitter-box section at the forward end and this gives a stepup of 0-775 to 1, making top gear an overdrive ratio of this value. Bottom gear in the 6-285 is 6-51 to 1, and in the TR 5-285 7-0 to 1; this allows an increase in maximum input torque to 350 and 320 lb. ft. respectively with these models. In the case of the TR 5-285 there are four ratio layouts, one of them incorporating a 0-756 to 1 overdrive top. Bottom gears vary between 6.74 and 8-4 and the input torque figures vary accordingly: the 8.4 to 1 bottom has a limit of 285 lb. ft., whilst the 6.74 to 1 has a limit of 350 lb, ft.
Gearboxes in the 360 range are based on the 5-360 unit—a five-speed box available with direct top or, overdrive top—and the pattern of the 285 unit is followed, there being a six-speed overdrive—the 6-360—with the overdrive gearing in a casing at the rear of the unit, and the TR 5-360 has step-up gearing at the front end. The direct top fivespeed and the TR 5-360 have bottom gears of 7-95 to 1, making the maximum torque 360 lb. ft., whilst the overdrive five-speed and the 6-360 have 6.6 to 1 bottom gears with maximum torques of 420 and 400 lb. ft. respectively.
The higher capacity boxes are the 6-650 and the 10-650, and there are alternative sets of ratios available in the sixspeed unit, giving either overdrive or direct top gear. Bottom gear in the direct-top model is 8.94 to 1 and input torque is 650 lb. ft. maximum. The overdrive six-speed unit (top gear is 0.71 to 1) has a 6.34 to 1 bottom gear and a maximum input torque of 800 lb. ft. The range change in the 10-speed unit is again built into the forward end of the gearbox and provides a step-up ratio of 0.758 to 1. In addition to giving an overdrive top gear this splits the five main ratios, providing 10 equally spaced forward ratios as well as a second reverse ratio. Bottom gear is 8.94 to 1 and maximum input torque is 650 lb. ft.
On all the new boxes clutch housings to suit Gardner engines, or to S.A.E. standards, are available and operation of the step-up ratios is by air. Control is by a push-pull button which can be located in a convenient position in the cab of the vehicle.