With the return below the oil level in the pan, obviously the pan oil will back up into the drain line.  I think Tracy made the key point.  If the oil is from the re-drive is “frothy” (which it likely is) it will “float” at the interface with the clear oil and back up the drain line; in other words, not drain.

 

This is a pretty good description Al.  For some reason, I’ve always thought there would be some oil pooled up in the redrive, but now that I think about it, I’m not so sure.  If there was a pool of oil, it would stand to reason that the frothy stuff would stay at the top, and the clear oil would be at the bottom, where the drain lines are.  Does anyone know if the drive does stay partially full when running? 

 

Cheers,

Rusty  

 

I'd love to see the drive in operation with a clear housing to know exactly what the oil is doing but this is not likely to happen.  

 

The design intent on the RD-1A/B was to have a minimum of oil remain in the housing.  Any oil remaining in the housing after passing through the gears & bearings is just lost energy due to churning.   If any of you have happened to remove the ring gear from the drive, you may have noticed that there is a centrifugal oil pump machined into the inside of the main housing.   The ring gear itself functions as the impeller.    The only evidence I have that it works is that the oil  temperature rise  through the drive was reduced after adding the pump.

 

Tracy