Gearbox + Diff running-in Oil?

[cap'n crunch]

Good Evening,

After a lot of forum searches I can't really find a definitive answer and i am hoping someone can help?

Should you use a particular oil type/grade/brand for running in New gearboxes and differentials?

Thanks

Alex

[TroonSprint]

I don't think it's necessary for transmissions. In an engine you are wanting a bit of friction in the early hours of running a new engine so that the piston rings will "bed-in" to the cylinder walls (ie. wear a bit). I can't think of any reason why you wouldn't want full lubrication from the outset with a transmission.

Mike

[Matt Elan]

I would agree with Mike re running in and I would drain and replace the oil after a few hundred miles or a few hours running to clear out any bits of metal generated by the initial running.

[denicholls2]

In a gearbox, the ability of the lubricant to protect the gear teeth where they mesh with each other is a big factor, because the torque applied there constantly is much greater then you'll see in any engine gears. Beyond that, the lubricant also needs to be thin enough to get through the bearings and synchros.

In an engine, the lubricant is about the (non-roller) bearings too, but the primary purpose is lubricating the parts that do the most moving, which are rings and piston skirts where a lubricant thin enough to build a film in tight clearances is desired.

Use of a 'running in' oil would be counterproductive against the requirements of a gearbox because it would put the gear teeth at risk.