All,
from http://www.vtr.org/maintain/lubricants-redline.html#gear-oil:
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Gear Oil
Gear oil viscosity is measured at 150 F vs. 210 F for motor oil. Therefore, 40 W
motor oil is the same as 95 W gear oil.
Gear oil is acidic, motor oil is alkiline. Gear oil needs very high wear
protection - Extreme Pressure (marked as EP). Therefore, it has a very high
sulfer and phospor content. Sulfur and Phosphate reactions start at a lower
temperature, and Gear Oil has much more additive than motor oil. This additive
is corrosive to copper bearings and bronze synchro rings.
Positraction additives are Friction modifiers - make the base oil much more
slippery. They coat the metal surfaces, and prevent the stick/slip mode of
operation, preventing shudder, and causes smoother take-up. Friction Modifiers
may detract from EP characteristics.
Friction modifiers cause smooth take-up of Limited slip units. For track racing,
FM is probably undesireable, and immediate take-up is more important. For
Street, FM is usually reccomended for more comfortable operation.
Gear oils decompose at lower temperature, usually 250 F.
Gear Lubrication Ratings
GL-1 No Additives
GL-2
GL-3
GL-4 Suitable for light duty hypoid sets
GL-5 Has lots of sulfer - Heavy duty hypoids
GL-6
Hypoid type gear sets have a sliding rather than rolling action, and therefore
require much greater wear protection.
GL-5 Should be used in rear differentials.
GL-6 is a heavier weight GL-5. Used for heavy trucks and Tow Vehicles.
Gear mesh in Gears litterally chops up and cuts apart the long polymer chains of
Viscosity Index improvers.
Smell of gear oil is from high sulfur content.
Quaiff Differential is a worm gear, and needs a very slippery oil.
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Also on the subject of Slick 50, this page says:
Slick 50
Lubrisol, Dema Elgin, a Ford Engineer all agree that it does not do
anything. According to Roy, to plate teflon on a metal needs an absolutely
clean, high temperature surface, in a vacuum. Therefore, it is highly
unlikely that the teflon in slick 50 actually plates the metal surface. In
addition the Cf (Coefficient of friction) of Teflon is actually greater
than the Cf of an Oil Film on Steel. Also, if the teflon did fill in
'craters' in the steel, than it would fill in the honing of the cylinder,
and the oil would not seal the piston rings.
Rich,
Your scinicizm is appreciated, howvever gear oil does contain the sulfer,
(its what you smell in the gear oil). Gear boxes do not generaly get hot
enough to cause the reaction(~175 C). Gear oil does need to be changed
periodically for this reason.
An old alpine transmision wizard once told me the reason that most english
cars use engine oil in the transmisions was because the gear clearances were
tighter than in american cars, also the EP additives in the gear oil gets
sheared by the closer running gears.
If you have a browser, please see this URL, for good literature on this
subject.
http://www.vtr.org/maintain/lubricants-redline.html#gear-oil
Jarrid
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