A gearbox can run horizontal, vertical or tilted on its side, but in each position the gears and bearings are immersed in oil differently. That is why a gearbox is lubricated for a specific mounting position and the breather plug is fitted at the point that will be highest in that position.

If the position changes:

  • a bearing or gear left at the top may not receive enough oil,
  • too much oil churns and increases heating,
  • if the breather ends up below the oil level, oil is pushed out and looks like a leak.

Practical rules: state in the order how the gearbox will sit on the machine (feet down, motor up, output shaft vertical, etc.); check the level at the plug after installation; if a gearbox was shipped with a closed plug for transport, fit the breather plug before commissioning. Oil quantity and type are determined by the gearbox nameplate and catalogue; if unsure, ask when ordering.