Can Someone Explain the Difference Between Hypoid
and Non-Hypoid Oil?
kick off this first issue of the New Year with an
often asked question about gear oils. But before
we get started, we would ask that your thoughts and
prayers go out to the victims and families of the
one of the largest natural disasters in history.
Please help in anyway you can and learn more by visiting
weekend I had the privilege to change differential
gears in a 4x4 pick up truck. As
the weekend was ending, I asked my son to pick up
some gear oil (80w90) for the project from the local
parts store and to make sure it was for “Posi-Track” (Limited
Slip) style differential gears.
at the parts store, he had many questions for the
counterman, but they were not much help. So I returned
to the parts store to get the oil and help explain
to the manager what the difference was between hypoid
and non-hypoid type oil.
assistance from industry insider, Andy Dingly, this
should help you and your team to understand the
difference of gear oils in today’s market place
and if Hypoid is actually what you are looking for.
"Hypoid" is not really a question of oil,
so much as a question of gear cutting. Old (1920's)
rear axles used straight bevel gears to form the crown
wheel and pinion. These had two disadvantages, the
pinion shaft meets the crown wheel on its central axis,
and the straight cut gears are noisy.
using a more complex "hypoid" gear tooth shape (if you
look at a pinion, the teeth appear twisted) these problems
can be addressed. The more gradual engagement of the
teeth along their length reduces noise. By careful
design of the geometry the pinion can be made to mesh
below the axis of the crown wheel. As the center height
of the crown wheel is fixed by the wheel height, this
allows the prop shaft to be lowered relative to the
car body, giving a cleaner floor pan and lower center
of gravity for better cornering. Hypoid bevels are
now universal in this application.
of the sliding contact that hypoid gears make, their
hydrodynamic contact pressure is higher. To be suitable
for use with hypoid gears, a lubricant must be capable
of resisting high pressures. Oils with "EP" ratings
(Extreme Pressure) such as EP90 are required. Some
brands describe themselves as "hypoid" instead,
a term which is synonymous with EP. GL-5 is a formal
API standard for this type of oil (comparable to MIL-L-2105B/C/D)
back to my installation... my owners manual
is telling me to use Non-Hypoid gear oil 80W or 80W/90
on the manual transmission and GL-5 hypoid gear oil
90W in the rear axle. A manual transmission won't
usually contain hypoid gears, so it doesn't need
exceptions are those transaxles where the crown wheel
and gearbox share the same lubricant. Although EP
oil is more complex to manufacture, it has no disadvantages
when used in instances where the EP attribute isn't
strictly required. Manual steering boxes and other
slow-moving oil-containing components are often filled
with 90-weight oil. It's usually okay to purchase
EP90 because that's what the axle requires, then
use the same oil for all other components.
is little practical difference between 80 & 90
weights. There's an increasing trend amongst manufacturers
to reduce the number of different lubricant types required.
But not all gearboxes are the same, so make sure to read
your owners manual. For example, a 5-speed Range Rover
runs on ATF, but 20W/50 engine oil or EP90 axle oil is
equally permissible, if the climate is of the warmer
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