1 comments
Truck gears, in the main,
require higher viscosity oils than do the gears in passenger cars. However, it
is difficult to generalize since any one manufacturer of trucks may employ a
variety of methods of speed reduction as well as perhaps more than one type of
differential. However, lubrication charts are kept up to date and such charts,
as well as the recommendations of the truck manufacturer should be consulted as
to the proper grade and type of gear lubricant to use. Lubricating charts
should be read with care because blanket recommendations are not made for all
trucks of a given make. Also footnotes are frequently used
to provide additional or more detailed
information about truck gear oils.
A number of truck
manufacturers depend upon specialty companies to provide them with
transmissions or axles. In this case the parts manufacturer may suggest the
most satisfactory gear lubricant. These firms often issue. Field maintenance
Manuals devoted to each type of speed reduction unit or each type of axle. Such
manuals generally contain sections on lubrication.
Almost all truck distributors
suggest some variation in the viscosity of gear oils used as the temperatures
change. A blanket statement cannot be made, but sometimes above 32 degree F
an SAE 140 grade of lubricant will be recommended
and below this an SAE 90.
While it has been
pointed out that lubrication would be simplified by the use of a
common lubricant for transmission and axles of
trucks, there is not an agreement on this. Thus, Nelson
and Valentine^40 mention that a rear axle lubricant must be
capable of absorbing greater torque or
providing better load carrying qualities
than a transmission, particularly in the
first three gears.
Fletcher^19 notes
that many fleets have standardized on the use of engine oils
in transmissions and cites a large bus line which has
used SAE 30 and modified SAE 10 engine oils in transmissions
for many years. The 30 grade is used in straight
mechanical boxes and the 10 grade when mechanical
transmissions are combined with a converter or coupling
and a common oil supply is required for
the two units. This author objects to the oxidation and sludging of
EP oils compared to straight mineral oils. His suggestion is the use of SAE 50
oil for transmissions. Another argument in favor of the
engine oils is that in corrosion tests, using bronze
specimens, such oils showed little corrosion whereas both HP
and MP oils showed excessive corrosion.
On the other hand, Calish^8
cites evidence of the practicality of the use of a common transmission and axle
lubricant in heavy equipment. A specific additive oil composition was used in
some 1420 vehicles representing sixteen makes of trucks. The inference is that
such a uniform transmission and axle lubricant proved satisfactory to the
thirty-four accounts operating the above trucks over a period of several years.
When transfer cases are used
to drive various devices, the same grade and type of oil as is used
in the transmission case will be satisfactory. Transfer case
is a term applied to gear assemblies which transfer power from
the main drive line to auxiliary equipment such
as front wheel drives, pulleys, hydraulic pumps, windlasses, and
other mechanisms. For example, many heavy duty utility
vehicles carry winches for erecting heavy poles, devices for
boring holes in the earth, and other tools which
must be driven from the same power source.
Where trucks are
equipped with automatic transmissions, ATF is
satisfactory for use and is so listed in most
lubrication charts. However, as a matter of economy,
General Motors suggests the use of a Hydraulic
transmission Fluid, type C for certain heavy duty trucks, buses,
and earth- moving vehicles. Type C does not have all
the characteristics of ATF but does have
to pass a Powerglide Transmission Test, have low
varnish and sludge deposits, and must have a
minimum effect on rubber seals. This Type C should never be
substituted for ATF where the latter is specified.
Truck Axle Lubricants.
There seems to be little question as to the necessity of EP gear oils in axles
of heavy duty trucks. However, there is not common agreement as to
the proper grade or viscosity of
lubricant for such applications. Johnson^27, who considered
these subjects, states:
“ Our field experience
is quite conclusive to the effect that an
SAE-140 viscosity lubricant is far superior to an SAE-90
in its ability to prevent gear wear and
related problems. On numerous occasions we have been
able to overcome gear wear problems by
merely effecting a change from an SAE-90 to an SAE-140
viscosity”.
Also, it was found that,
with the heavier gear oil, temperatures in the gear case did
not increase but actually were 5 to 10 degree F lower
than when operating with the lower viscosity oil.
The use of SAE 250 gear oil was investigated but it
was found that this did run hotter than the SAE
140 grade.
A further
advantage of the use of the higher viscosity oil
was found by this investigator^27 when the two
grades of hypoid lubricants were tested on eighteen driven units in
the laboratory, using hypoid gears with a 61/6 ratio. The results
obtained were:
“At 3000 rpm, the SAE-140
lubricant supported a torque load 21% greater than the SAE-90. At 2500 rpm, the
advantage was 23%, and at 2000 rpm, it was 20%”.
Another factor, indicating the
desirability of higher viscosity oils in axles of trucks, is that pointed out
by Blok^3. It was mentioned that, under conditions
of impact load on gears, viscosity is of prime
importance and that this property of the oil
cannot be replaced by antiwelding activity if
wear is to be prevented.
Gears in heavy duty
trucks are subjected to low speeds and high
torque conditions during much of their operation. For example,
Nelson and Valentine^40 determined that in highway operation
a truck having a 5-speed transmission used first speed about 2 per cent
of the time, second speed about 3 per cent, and third speed
about 10 per cent , or a total of 15 per cent. The resulting comment was:
“It is in this interval that gear destruction is prevalent, if the lubricant
does not have proper EP qualities”. Further, mention is made
that in off -high way service, such trucks operate
approximately 50 per cent of the time in the
first three transmission gears.
Not all EP gear oils will
provide satisfactory protection to axle gears operating at low speeds, and high
torque, as do those in trucks. Therefore, assurance should be
obtained that lubricants satisfactory for such service are
used for truck axles. Lead soap active sulfur EP lubricants
have been favored by some for such application. Since the prevalent
operation of passenger cars is under high speed
and low torque conditions, it is desirable that a single
type gear oil satisfy these conditions as well as
those of operating trucks. With this in mind, what is considered by
some as a truly multipurpose gear lubricant has been provided? Such oils are
those conforming to specification MIL-L-2105B
which is accepted for the requirements of all
vehicles operated by the U.S Military and by many
other users.
Some axle manufacturers and
truck producers prefer to either issue specifications for
what they know to be satisfactory axle lubricants
or to state the type of EP gear oil to employ.
Hence, it is well to abide by the opinion of the truck supplier when choosing
lubricants for truck axles.
This is all the more true
because the gearing in truck axles may vary. Most of such
variations, with the exception of worm drives, will probably
require the same type and grade of
gear oil as will straight hypoid gears. Thus,
Rockwell standard for either Planetary Axles or Hypoid-
Helical Two- Speed Double-Reduction Drive Units, as well as
Spiral Bevel Gears, recommend oils conforming to their
Standard 0-65, which is an SAE 140 EP product.
Use of Standard 0-65, the SAE 90 grade is optional but is suggested for lower
operating temperatures than the 0-65.
Lubrication of Worm Drives on
Trucks. In the case of worm drives on trucks, recommendations for the lubricant
vary. While some suppliers of EP gear lubricants claim such oils can be
used safely in worm drives, Watson^51 states:
“Actually, in practice, an EP
lubricant is usually unnecessary for a worm gear. When lubrication failure
occurs in a rear-axle worm gear, only in exceptional
circumstances can it be attributed to lack of load
carrying capacity of the oil used”.
Certainly if
temperatures exceed 200 degree F, as they may at times
in axles of any large vehicle, EP additives may cause
excessive corrosion of bronze. Since EP agents and combinations of the
same cover such a wide range of chemical compounds, the above statement may
require modification. Perhaps the worst offenders are sulfur compounds, even
some not considered active at 200 degree F. The possible explanation
may be that since copper has considerable
affinity for sulfur, temperatures at contact
points of the gear and worm will be
high enough to cause reduction of the metal and
sulfur. That, is the action may be akin to temperature flashes which occur with
hypoid gears.
However, substitutions
have been made for recommended worm gear lubricants; and if
this is done, fleet operators are in a better position
to observe result than are individual vehicle operators.
In certain busses of the London Transport Company
having worm drives, it was reasoned that a fuel saving
would be possible if there was less drag due to the
axle lubricant. An exceptionally thin oil gave satisfactory
lubrication, but when changing from first to second
gear on a level road, the lay shaft spun so
freely that the higher gear could not
be engaged until the bus came to rest. An inhibited
castor oil was then tried and proved satisfactory. However, the operation of
these specific vehicles with considerable stop and
start does not result in heating of the axle
lubricant, with a consequent possibility of oxidation, as would be
the case in over-the –road vehicles.
While possible variations in
oils for servicing worm gears of trucks have been mentioned, this is for
information only. The safest course for the owner
or user of such a truck is to follow the recommendations
of the manufacturer of the equipment.
