915 ring gear backlash

[pjh69911]

Is the spec .12 to .18mm to be set at room temp? I just thought about this as my garage was only about 50 degrees. I am thinking as the temp rises, the pinion will pull away from the ring gear and backlash will increase. For a 50 degree C rise, I estimate a .004 inch movement for the pinion. Sounds like a lot...An insight is appreciated.

[kevingross]

You are thinking too hard.

[Jon B]

Originally Posted by kevingross

You are thinking too hard.

No, he's not thinking hard enough.

He hasn't considered the thermal effects on his pinion, ring gear or differential, the coefficient of expansion for different alloys involved, or difference in operating temps of various parts involved.

[Matt Monson]

A 50 degree Celsius garage? I would pass out.

[pjh69911]

Well my garage was 50 Fahrenheit, and expansion coefficient of aluminum is roughly 10 times that of steel. So steel expansion though likely hotter at the gear interface, is not 10X given it is bathed in oil. I figure a gearbox would easily rise 50 degrees C or more at the track.

[Jon B]

Originally Posted by pjh69911

...expansion coefficient of aluminum is roughly 10 times that of steel.

It is roughly 2 times that of steel.

[pjh69911]

Thanks for the correction on expansion!