>I'm nearly up to 12,000 miles on my 97 truck (2WD) and the owner's manual says o> change the transmission and rear differential fluids at 12K (following the hi
Do the fluid change -- and make sure they really change it, and you don't
get a "wall job". Or do it yourself!
If you're not in a dusty environment, going to 20-25,000 miles won't hurt
your diff at all. Manufacturer's these days are getting away from recommending
break-in periods because of the tight part tolerances. The parts still
break-in though, they just don't generate as much in the way of debris.
I switched to synthetic lube at about 40K, but I'd done a break-in change
at about 20K. I now have an additional 80K on the synthetic lube, and I'm
about ready to change it. I have a 4x4, and the limited-slip rear. The
L-S clutches demand special additives, which age and deteriorate even when
the fluid itself is fine.
BTW someone else had recommended changing rear diff lube for a truck backed
into the water at a boat ramp. This is mandatory!
The air in your nice warm differential will shrink in volume as it cools, andck water in in its place. Normal diff fluid uses stinky sulphur compounds
as friction modifiers (to deal with the shearing forces on the ring gear).
When these compounds react with water, you get sulphuric acid, which does
bad things to steel. Both the front and rear diffs on a Dak 4x4 have remote
vents, but only to the wheel wells. If you can float a boat into the bed,
you certainly had the vent under water too.
Redline synthetic doesn't use sulphur friction modifiers, but the tradeoff
is that it doesn't have the same high-shear protection. I use it, but then,
I don't drag race either. AMSoil synthetic, and probably most others, use
conventional modifiers.
Jim
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