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On 2007-04-14 09:03, allenman85 wrote:

Please explain and quote at least one engineering text.

I am waiting. Intuition (yours) is not an acceptable answer.

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Ok, I have wasted some of my own time and have found an engineering text to back up my "intuition", which I would prefer to call logical thinking.
It is from a NASA paper 1622 by Anderson & Loewenthal regarding gear efficiency under load.
The paper pertains to a large helical gear setup that is running at a constant speed of 1450rpm. As load increases from 25% thru 100% frictional gear losses increased from .3 thru 10.8kw.
To quote from the text - "it can clearly be seen that the sliding friction losses are heavily load dependent, increasing with load."
Whilst I could not find anything directly relating to automotive applications but would imagine that the results would be relative to smaller diameter gears with higher teeth to diameter ratio's. The bottom line is that gear friction rises with load.
Keep in mind that these tests were conducted with a single helical gear in parallel configeration (think manual main and lay-shaft layout) with a 25 deg helix. It is also travelling at a relatively slow speed.
A rear end has a hypoid configeration with a larger degree helix and much more tooth contact area, plus the pinion is placed low relative to the crown wheel.