Given that I'm about a week behind, you've probably already buttoned up the
Spit diff. My suggestion would be to look for Castrol Hypoy gear lube at
one of the local auto supply places. It is a decent GL-5 lube that works
well. If you had more time to wait for shipment, a better lubricant would
be one of the Redline synthetic GL-5 oils. Gee, I thought I had the Fat
Chance prices for Redline lubes handy. Oh well, no commercial today.
In a diff, the pinion gear teeth slide along the ring gear, unlike in the
gearbox where the mesh of the teeth is more direct. So, a GL-4 rated lube,
intended for gearbox use, like Redline MTL or MT-90, is optimised more for
compression loads on the film.
In a diff, the lube needs more shear strength. The most common stuff
added to boost the shear strength of the oil film involves sulfer compunds.
Which is why diff oil, even fresh out of the box, really does smell like it
came from something that lived millions of years ago. It also explains why
putting GL-5 oils in a gearbox can wear out the yellow metal parts, as various
sulfuric acids are formed under the heat and pressure as the oil breaks down.
This is less of a problem in diffs, though in the big TRs the thrust washers,
having a high copper content, on the spider gears do wear out, giving more
slop in the whole works.
But if you used a major brand of hypoid rated oil in the diff, it should
work just fine.
mjb.
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