jonmac wrote:
>
> On August 25, Andy Mace wrote:
>
> > Gearbox and differential oil don't need to be changed at all -- only
> > topped up as needed.
>
> Andy, I'm not challenging in any way what you have written and I know this
> is what the factory recommended in days of yore. However, I have long been
> of the opinion that this was a shortcut on Triumph's part to reduce owner
> servicing costs - and I'm not too convinced whether it was really the right
> way
> to go about things.
The unfortunate part of this is that some diffs simply don't have drain
plugs, further fostering the belief that topping up is all that's
necessary.
> Over the years, I've speculated on how long an oil can reasonably be
> expected to last and still do the job. I know nothing at all about the
> chemistry of the oil industry but I know things called polymers are present
> in oils which presumably are there to protect and keep the oil in good
> order. What happens to these polymers through the undoubted shearing action
> they must encounter as the diff or gearbox is working? The tooth loading on
> a crown wheel and pinion must surely be many tons per square whatever and
> how long can an oil REALLY last? I have to say I've never subscribed to
> this 'lifetime' oil claim and I've changed the oil (with difficulty) on a
> number of occasions because I don't see how it can be expected to go on for
> ever. Does anyone want to comment and allay my concerns?
The only polymers I know of being introduced into the oil here are the
so-called Teflon additives. These claim to coat the innards with PTFE
(poly tetra-fluoro-ethylene, some sort of Teflon derivative) resin.
Every machine shop I've talked to says one might as well throw out the
pieces when they wear out, since the stuff coats everything, and makes
it impossible to repair if regrinding is required anywhere.
The real problem with any gear oil is that, because of current
multi-weight formulations, they seem to be slightly hygroscopic. Despite
all the additives and blah-blah-blah, they still take on a little water,
and can get overheated, which pretty much destroys any of the
life-preserving additives, anyway (if the fluid's dark, and smells a bit
burned, it is...). Labor included, crown wheel sets and bearings are
much more expensive than fresh gear oil.... <smile>
Cheers.
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