In a message dated 96-03-13 21:13:18 EST, skillman@clark.net (Robert E
Skillman) writes:
>t
>
>Have followed gear lube threads and now that everyone knows how to get it
>in the transmission some other thoughts:
> I'm trying to get exact specs but I think I remember from somewhere
>that 80-90 weight gear oil has about the same viscosity as 30-40 weight
>motor oil. Apparently the powers-to-be gave gear oil different
>nomenclature so Bud or Earl didn't fill your engine crankcase with it.
> I've had several NON-OVERDRIVE mgs which have had both gear oil and
>engine oil in the tranny at some time. Although the book calls for engine
>oil I wouldn't worry about gear oil in your transmission (non-overdrive).
WORRY.
Although you are basicly right about the viscosity, one difference is that
the oils are rated at different temps, the rearend lube having less heat
tolerence than the box/engine oil has. (Very Important)
Now the Big Problem: (First, as you correctly implied, ENGINE OIL ONLY in
Overdrive boxes! No discussion, no argument, period. Any other oil will cause
the OD to fail.)
But on to the problem...Syncros! Yes those wonderful,Brass rings that keep us
shifting. Well, guess what? The Additives in gear oil, when they heat up and
break down, render chemicals into the mix that corrode... Brass! (which is
also used for a couple of important bushings as well in the B box, if I
recall...)
72 or so and later TR6 boxes used steel sycros, which is when they changed
their recommendation for lube to gear oil. To my recollection, they are the
only boxes among the common (TR, MG, AH) LBCs that can get away with using
gear oil.
The moral of the story...there are reasons for why the factory did what they
did, and occasionally the reasons are even right!
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