How do you change gears on a dump truck without grinding the gears?

Answer 1

Gearboxes on trucks are generally not synchromesh. It means there is no mechanism to automatically adjust the speed of the engine and the gearbox to match. Therefore if we would simply change gears like in the modern passenger car equipped with the synchromesh gearbox by depressing the clutch and shifting the gear up or down before releasing the clutch the different speeds of the engine and the gearbox would cause the grinding. To avoid this change requires process called double clutch. It goes like this: 1. Depress the clutch, 2. Shift the gear into neutral, 3. Release the clutch, 4. If shifting down depress the accelerator to rev up the engine so the rpm's of the engine are slightly higher than the gearbox and release it; if shifting down depressing the accelerator may not be necessary if the whole process is done quickly enough, 5. Depress the clutch again - that's why it is called double clutch, 6. Shift the gearbox into next gear (up or down). At this stage the rpm's of the engine will be slightly higher than the gearbox and the engine will be slowing down at some point the speed of the engine and the gearbox will match and the gear will go in without grinding. This needs to be done with the feel and with the bit of practice it becomes automatic. The amount the engine needs to be speeded up will depend on the conditions for example if changing gears when going up the hill.