[alfa] remove the filler plug before the drain plug

["Jay Mackro" <jmackro@xxxxxxxxxxxx>]

"Dean W. Cains" <dwc@domain.elided> had written:

> And, always  remove the filler plug before the drain plug,
> for reasons I'd rather not  remember, although a gearbox
> was involved.

Hmm - I can't figure out why that would be important.  At first
I thought "sure, you need to let air into the differential in order
for the fluid to drain quickly and completely".  But then I
remembered that the diff has a little piece of hooked tubing
welded to one of the axle tubes that admits outside air (I
guess so that pressure can't build up inside the diff, and
push oil out through the seals).

So, why take out the filler plug first?  Is this like when you
disconnect a battery, you remove the ground wire first?
That one I understand.  Both differential plugs need to
come out anyways when you are changing fluid, so I guess
it doesn't hurt to start with the upper one.  But, why?

Sorry to put you on the spot Dean - Jay Mackro
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