Posted by Tech Dept/Red Line on 9/18/2014 to
GEAR AND SYNCHRONIZER WEAR PROTECTION
Most manufacturers of manual transmissions and
transaxles recommend an 80W or 90W GL-4 lubricant.
GL-5 gears oils which are required in hypoid differentials
are not used in most synchromesh transmissions.
The chemicals used to provide the extreme
pressure protection can be corrosive to synchronizers,
which are commonly made of brass or bronze. Typically,
the use of a GL-5 lubricant in a synchromesh
transmission will shorten the synchronizer life by one
half. The extreme pressure requirements of spur gears
and helical gears found in transmissions are not nearly
as great as found in rear-wheel drive differentials. A
GL-4 lubricant provides adequate protection for most
manual transmissions, unless a unique design
consideration requires the extra protection of a GL-5.
The reason that many manufacturers have made
recommendations of motor oils or ATFs is that petroleum
80W gear oils frequently do not shift well at low
temperatures. Motor oils and ATFs are much more fluid
at lower temperatures and they are not corrosive toward
synchros, but they provide very poor gear protection.
These lubricants provide almost no extreme-pressure
protection. In addition, petroleum multigrade motor oils
and ATFs have very poor shear stability. The shearing
action by a manual transmission on thickeners is much
worse than in an engine or automatic transmission.
Within 5,000 miles the thickeners can be rendered
ineffective and the transmission will be operating on a
much reduced level of protection. In hot weather these
transmissions will whine
and rattle because of poor vibration dampening and
metal contact. This is why we recommend and use Red Line MTL
and MT-90 to provide the
excellent gear protection of a GL-4 gear oil in a synthetic
lubricant which spans hot and cold temperatures and will
not shear or oxidize with use.