The manufacturer
of automotive equipment
almost universally specifies
the proper gear
or transmission oil to
use in a given model. Few
users deviate from such
recommendations; and consequently, information relative to suggested lubricants is
widely circularized, not only
in instruction and
bulletins for customers
and dealers, but also in wall
charts which are
provided for service stations
and service departments dealing
with automotive vehicles.
Such charts
use coding with
notes starting what the
code letters signify. For example, the following are used
in lubricating charts which have wide distribution:
AF – Automatic Transmission Fluid, Type A
AFA -
Automatic Transmission Fluid, Type A, suffix A
EP - Extreme Pressure Gear Lubricant
GL -
Straight Mineral Gear Lubricant
GL4 -
Multipurpose - Type Gear Lubricant
HF -
Hydraulic Transmission Fluid, Type C
HP -
Hypoid Gear Lubricant
MP -
Multipurpose Gear Lubricant
WL -
Worm Gear Lubricant, Heavy- Duty
In addition to the above
coding, other designations of
gear and transmission lubricants will be found
in instruction manuals and in
lubricating charts, and it is wise
to read any footnotes
and conform to the
recommendations. Thus, a gear lubricant meeting the requirements of
Military Specifications MIL-L-2105 or MIL-L- 2105B may be required. Many gear
oils, offered by service stations will meet such requirements as well as classify under EP, GL4, HP and MP. However ,
it might be noted
that GL4 is an API
designation and that products so designated
are generally accepted
as of higher performance
level than those qualifying
under MIL-L-2105. If in doubt as
to the classification of a gear
lubricant, the oil supplier will conform the
fact that certain of his branded products satisfy stated requirements.
Since all
gear oils which can be classified as EP, GL4, HP or MP will not contain the
same EP additives, their performance in service may vary. Also the period requiring the most
effective action from EP additives is during the
break in of the gearing.
Consequently, a number of
automotive manufacturers use a
gear oil containing
an SCL additive in the
initial fill of axles. This SCL indicates that the
additives contain sulfur, chlorine and lead. Use of this
particular combination in factory fill does not mean
that some other combination of additives would not be satisfactory
but does indicate that the
manufacturer is reasonably
satisfied with what
they use. Most EP lubricants
are compatible and
consequently makeup oil
or refill need
not be of the identical
composition as the oil in the
gear casing. Also, after the
break in it is possible to adds
a small proportion
of straight mineral oil, provided the oil
level is low and no
other oil is
available, without damage to
the gears. This is not advisable, and as
soon as the proper EP
oil is available, the diluted
oil should be removed
from the gear
box and a
refill made with the proper lubricant. It might
be kept in mind
that manually operated
transmissions do not require an EP
oil. The latter type of lubricant is used largely as a matter of convenience
and uniformity. More will be said about this subject when consideration is given to choice of oils for
trucks.
A cooperative effort has been underway
for several years to
reduce the number of
specific axle and transmission lubricants so
that a service
station or service
department would have
to stock only one
truly multipurpose gear
lubricant. Gear oil conforming
to specification MIL-L-2105B
are said to
solve this problem
since such lubricants will satisfy
vehicle operation of gear under
conditions of both high speed
and low torque and
low speed and high torque.
Several reasons preclude the adoption of a universal gear lubricant for
automotive vehicles. Thus: (a) the possible
variation in automotive equipment may demand a like variation in lubricants.
(b) no sooner is a composite
demand for such a
product met than
an improvement or
change in mechanisms
necessitates a corresponding
change in the
lubricant and (c) all
organizations do not obtain
identical service results
with a given product. Added to this
is the economic factor in that
there is no need to
use more expensive
lubricants than those which
have been found satisfactory.
Since the demands
required of gear and transmission
lubricants are not static, service people and owners
of vehicles will do
well to conform
to the latest recommendations of
the manufacturer of the equipment. Many vehicles
are used under
widely varying climatic conditions and consequently
variations in viscosity of gear
oils are often desirable.
Oil compounds have so improved the
viscosity temperature
characteristics of most
grades of gear oils that
it is only under extreme conditions
that seasonable changes of
automotive gear lubricants
are necessary. Also multi grade gear
oils are available from some sources. The
U.S. Department of Defense
provides a sub zero gear
oil, equivalent to about
an SAE 75, which is
designed for Arctic conditions. Under such circumstances, civilian automotive
operators are prone to dilute the
lubricant with a little 5W
motor oil or even kerosene. If this is done, the gear case
should be drained and refilled with the
proper grade of lubricant with the advent of warmer weather.
Where changes in grades of
automotive gear oils are desirable, due to temperature changes, the practice is
not uniform. Therefore, SAE^47
makes the following
suggestions: “In
recommending gear lubricants based on lowest atmospheric temperatures the following are suggested as a uniform practice
in making such recommendations: plus 32
degree F, plus 10 degree F and minus 10 degree F”.
