John Hobson wrote:
> I was browsing through my moss catalogue today and noticed that they
> advised not using EP90 in gearboxes with overdrive. Apparently even
> though Triumph recommend EP90
It's very likely that the gear oil from then and now are
very different, and that is what is causing the issues.
The specifications should be consistent, but thirty years
of progress might mean that the oil that is labelled EP90
today actually exceeds the original oil on many tests.
> Laycock de Normanville(the OD makers)
> recommend using a non-hypoid oil(what does hypoid mean?)
As mentioned, hypoid is a type of gear profile.
Basically, a hypoid gear is designed to be quiet, compared
to a straight cut gear. (think of a formula 1 car or a
japanese car in reverse whining away)
In a hypoid gear the teeth are spiral and they slide
accross one another as they mesh, so there is a great force
applied on two surfaces that are also sliding against
each other.
"Hypoid" oil is designed to not break down under these
situations, so even as the film is under extreme sliding
and squeezing, it will maintain an adequate lubricating
layer.
Sadly, this ability to maintain a slippery layer under
extreme pressure is what sometimes causes overdrives to
not work. An OD cone clutch is basically two surfaces pushed
together under great pressure, and they have to lock up
even though they are swimming in oil.
My J-type was inconsistent no matter what gear oil I
used, so I used motor oil and it works fine.
This isn't too absurd, many cars (MGBs, early spridgets)
spec motor oil for their gearboxes and Laycock overdrives.
--
Trevor Boicey, P. Eng.
Ottawa, Canada, tboicey@brit.ca
ICQ #17432933 http://www.brit.ca/~tboicey/
Any part can be removed with the careful application of too much force.
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