Wheel bearing pre load

updraught

updraught

Well-known member
There is a discussion is raging on a camper trailer forum I'm on where someone asked about adjusting wheel bearings. These trailers are usually used in the outback where things have to work, and conditions are often less than ideal. Mechanics are usually good with a hammer and a welder, and are judged by their competency of both.
My understanding is that bearings running in oil such as a A diff are OK with pre load. The oil gets replaced and does the cooling.
However, with greased wheel bearings there needs to be a small gap for the grease to run and the bearings need to run cool. So ideally, you tighten the bearing, back it off, do it up finger tight and drop in the split pin. Ideally, you have no wheel play and no pre load on the bearing.

There is a youtube video where they go thru a complicated wheel bearing adjustment procedure and end up measuring the play in the hub with a gauge (back and forth along the axle). They say it should be one to five thousands of an inch.
Just wondering what the engineering school of thought on greased bearing pre load is?
 
Here's a link to the Timken site.


Never mind had wrong link, now can't find the right one.
 
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If the nut spins easily on the spindle threads tighten down with wrench while spinning then loosen and tighten with 2 fingers and back off to closest cotter pin hole.
 
Bob C said:
Here's a link to the Timken web site for bearing adjustment.
https://www.timken.com/resources/md11-nut-torquing-and-back-off-to-set-wheel-bearings/
Click to expand...
I should be noted we do not own "medium" duty vehicles. If you put 200 ft pounds on the front spindle of a (Class 1) Model A it will no longer have any threads or be in 2 pieces.
Medium duty are trucks with 10,001-26,000 GVW

https://cmvid.nisrinc.com/CMV_ID/GVWRClass.asp


Many years ago we had a Timken guy come to work and talk on maintenance. He stressed don't blow them dry after cleaning - sound neat but doesn't do the bearing any good. He also said everyone puts too much grease in. He likened it to running on the beach - if the water is too deep it slows you down so less grease is easier for the bearing to run. He said it will pretty much throw off what it doesn't need but it's wasteful to over pack them.
 
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Here is my technique. First I firmly tighten the nut to seat the bearings. Then I back it out and tighten it only with low torque. Then back it out one cotter key position. The wheel should turn freely with no play. Very much as the video shows but without the dial indicator.

Many years ago, as a teenager, I would melt the grease over a hot plate and put the bearing in the melted grease to saturate it. Now I just jam the grease in the bearing as the video shows.
 
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This is the factory technique of adjusting wheel bearings: "....... tighten the adjusting nut until the hub just starts to bind. Then back off the adjusting nut one or two notches until the hub can be freely revolved." There is no preload of the wheel bearings. I have been adjusting wheel bearings this way for many years without any issues.
 
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