Hi List-
In my work in the Heavy Duty truck industry theres a lot of debate recently
and interest in bearing lubes- currently most trucks use oil type lubes in
the wheelbearings and a move has been afoot recently to a semi liquid
lubricant. The hope was to reduce costs (as always) and catastrophic
failures due to seal leaks. Basically whats happening, is the big trucks are
being converted from 80-90 gear oil in bearings to semi fluid greases, much
like cars use currently.
Some of the information and experiences may be relavant to GMC owners. In
particular, using greases instead of oils in the truck bearings has led to
significantly greater problems with 'fretting corrosion'. This was never a
big problem before they switched to greases, really- but this is old hat for
us, fretting corrosion is a typical failure mode for light vehicle bearings.
Fretting corrosion is a condition where metal to metal contact of bearing
parts occurs, leading to small metal paticles being spalled off, and
subsequently forming extraordinarily hard (and abrasive) ferrous oxide (rust
essentially) crystals. In as little as two-three months after service this
damage can occur. This damage is particularly possible at extremely low or
high temperatures. The hard crystals will eventually grind the bearing and
spoil the surfaces and clearances, leading to failures.
It appears slightly red like rust on a cleaned bearing. If lubrication is
present, it will look black. Those of you currently servicing bearings
should look very closely for evidence of damage while the parts are loose.
According to an article I have in a trade magazine, Lorne Brock, senior
technical specialist for Imperial Oil in Canada (Exxon to you in the states)
says the only real solution is a moly grease, 'because we know it works'.
Graphite may also be helpful, he says, but is not generally regarded as
compatible with wheel bearing greases and hence, is not likely to be useful
in his opinion.
For what its worth, moly greases have a distinctive odour, and if you are
servicing bearings, you may wish to check the content out with your
supplier. Moly additives are very common since about 1961 in lubricants for
'sealed for life' type assemblies like power window motors and Cadillac ball
joints, as example. Moly additives possess a somewhat sour odour, and dark
colouring in greases. GM Engine Oil Supplement, and most of their other
chemical products contain significant moly additives, as do many other
brands.
Many aftermarket expensive supplements contain some moly content, but
generally are just overpriced garbage and I would not recommend them. You
can get sufficient moly content without resorting to Infomercial type
products, the vast majority (perhaps universally) of which have zero value.
Hope this is helpful information to some of you;-)
Brent Covey
In my work in the Heavy Duty truck industry theres a lot of debate recently
and interest in bearing lubes- currently most trucks use oil type lubes in
the wheelbearings and a move has been afoot recently to a semi liquid
lubricant. The hope was to reduce costs (as always) and catastrophic
failures due to seal leaks. Basically whats happening, is the big trucks are
being converted from 80-90 gear oil in bearings to semi fluid greases, much
like cars use currently.
Some of the information and experiences may be relavant to GMC owners. In
particular, using greases instead of oils in the truck bearings has led to
significantly greater problems with 'fretting corrosion'. This was never a
big problem before they switched to greases, really- but this is old hat for
us, fretting corrosion is a typical failure mode for light vehicle bearings.
Fretting corrosion is a condition where metal to metal contact of bearing
parts occurs, leading to small metal paticles being spalled off, and
subsequently forming extraordinarily hard (and abrasive) ferrous oxide (rust
essentially) crystals. In as little as two-three months after service this
damage can occur. This damage is particularly possible at extremely low or
high temperatures. The hard crystals will eventually grind the bearing and
spoil the surfaces and clearances, leading to failures.
It appears slightly red like rust on a cleaned bearing. If lubrication is
present, it will look black. Those of you currently servicing bearings
should look very closely for evidence of damage while the parts are loose.
According to an article I have in a trade magazine, Lorne Brock, senior
technical specialist for Imperial Oil in Canada (Exxon to you in the states)
says the only real solution is a moly grease, 'because we know it works'.
Graphite may also be helpful, he says, but is not generally regarded as
compatible with wheel bearing greases and hence, is not likely to be useful
in his opinion.
For what its worth, moly greases have a distinctive odour, and if you are
servicing bearings, you may wish to check the content out with your
supplier. Moly additives are very common since about 1961 in lubricants for
'sealed for life' type assemblies like power window motors and Cadillac ball
joints, as example. Moly additives possess a somewhat sour odour, and dark
colouring in greases. GM Engine Oil Supplement, and most of their other
chemical products contain significant moly additives, as do many other
brands.
Many aftermarket expensive supplements contain some moly content, but
generally are just overpriced garbage and I would not recommend them. You
can get sufficient moly content without resorting to Infomercial type
products, the vast majority (perhaps universally) of which have zero value.
Hope this is helpful information to some of you;-)
Brent Covey
