8/23/02
James and the group,
From what I think I know, I would say that this information is
right on the money. The 2 key issues involved in "Hypoid" gears are: 1)
the lowered driveline in relation to the centerline of the rear axle, and;
2) the sliding contact of the curved hypoid-cut gear teeth. This sliding
contact is along the length of the teeth, not in and out, in relation to
the centers of the 2 gears. It is this sliding contact which the EP
formulation of the oil must withstand. The tendency of this sliding motion
is to wipe away the oil film and these oils must successfully resist this.
Only hypoid gear teeth behave this way. I did know that the "hypoid"
designation of an oil is sufficient, but did not know about the API
(American Petroleum Insitiute) GL-5 or Mil-Spec designations mentioned. I
do not know to what extent non-hypoid gear oils are available. If there is
any question as to whether the ring and pinion gears in any particular
differential are hypoid (They practically all are) it is an easy matter to
look underneath the car and see if the driveline & pinion shaft intersect
the axle housing below the centerline of the axle shafts. If so, then,
Presto, you are looking at a hypoid gear set.
Cheers,
Dave Kernberger
------------------------------------------------------
>"Hypoid" is not really a question of oil, so much as a
>question of
>gearcutting. Old (1920's) rear axles used straight
>bevel gears to form
>the crownwheel and pinion. These had two disadvantage,
>the pinion
>shaft meets the crownwheel on its central axis, and the
>straight cut
>gears are noisy. By 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 crownwheel. As the
>centre height
>of the crownwheel is fixed by the wheel height, this
>allows the
>propshaft to be lowered relative to the car body,
>giving a clearer
>floorpan and lower centre of gravity for better
>cornering. Hypoid
>bevels are now universal in this application.
>
>Because 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)
>
>> The book is telling me to use Non-Hypoid gear oil 80W
>or
>>80W/90 on the manual transmission and GL-5 hypoid gear
>oil 90W on
>>the rear axle.
>
>A manual transmission won't usually contain hypoid
>gears, so it
>doesn't need an EP oil. Rare exceptions are those
>transaxles where the
>crownwheel and gearbox share the same lubricant.
>Although an 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 usual to buy EP90
>because that's
>what the axle requires, then use the same oil for all
>other
>components.
>
>There's little practical difference between 80 & 90
>weights. I fill
>everything with EP80 and I've never had a problem.
>
>There's an increasing trend amongst manufacturers to
>reduce the number
>of different lubricant types required. My own gearbox
>(5 speed Range
>Rover) runs on ATF, but 20W/50 engine oil or EP90 axle
>oil are equally
>permissible.
>
>--
>Andy Dingley
>dingbat@codesmth.demon.co.uk
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