I can't find anyplace in my Freightliner manual about how often to change the fluid in the front hubs of XC chassis. The book tells all about packing and adjusting the front bearing but nothing about how often to change the fluid in oil bath bearings.
What kind of schedule do any of you use, other than checking the level before each trip? I've been doing it every two years but got to wondering if this is necessary.
Correct place to look would be your axle manufacturer's website.
And every 3 years/50,000 miles which ever comes first should be fine. BTW, as little oil as it takes (less than a quart for both wheels) I use synthetic gear lube of the viscosity recommended by my axle manufacturer.
I just use a suction pump to remove old oil, fill, suction out again and refill to proper level. Be sure to recheck after 10 or so minutes, particularly if cold, as it takes a little while for the oil level to reach equilibrium.
Every 2 years I raise the wheels, rotate them to get the drains down, install cardboard "funnels" and let them drain the old fluid for a day or so, inspect the fluid color, odor, and look for foreign particles, replace the plugs and slowly, very slowly, refill to the full indicator line. After filling, rotate the tires while listening to the bearings. Also check for free play or tightness of the bearings.
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I have a friend that works in a shop that has a 100+ unit fleet of medium to large trucks. He says they watch for leaky seals like a hawk. They pull the hubs, inspect the bearings, brakes, replace seals, etc every 100K but they put miles on much faster than we do.
I watch for leaks routinely, will replace fluid at 50K which will be about the five year mark.