Tuesday, June 27, 2017 Detailed Auto Topics
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They design most vehicles today, with sealed wheel bearings. These sealed bearing do not require service. Millions of trucks, trailers and cars also have wheel bearings that periodically require service. Serviceable wheel bearings are inexpensive and give long life. Improper service will also quickly destroy a serviceable bearing.

What service do bearing require?

All serviceable wheel bearings require maintenance. At specified intervals, we remove the bearings, clean and replace the lubricant. We also replace the seals that protect the bearings.

Technicians often use the term, packing the bearings to describe this service. When we pack the bearings, we also need to properly adjust them. Adjusting serviceable wheel bearings is something that normally does not get much thought. Even many experienced technicians do not adjust wheel bearings properly. When improperly adjusted, premature failure is the normal result. Severe damage can occur, to the bearing, hub and spindle.

lubricant between the rollers requires space

This cross section shows a typical roller type wheel bearing. The red area, between the rollers and the races are the space where lubricant has to be. 

Why bearings need end play

When bearings rotate, under a load, they generate heat and the rollers expand slightly. This expansion takes up room, where the lubricant must fit. If end play does not provide space, the lubricant will be forced out. When this happens the rollers contact the races and damage quickly occurs.

bearing ruined by improper adjustment

They improperly adjusted the bearing in the photo above. In only 5,000 miles a lack of lubrication has destroyed the bearing. Expansion forced the lubricant out of the spaces where it needed to be.The bearing has been destroyed. The metal flakes show damage to the rollers, resulting because the bearing was adjusted too tight.

Serviceable wheel bearing are use used in pairs. The inner bearing is normally larger and carries much of the load. The outer bearing balances the load and also adds support. When the bearings are assembled and adjusted, end play must be allowed. This end play, normally .004 to .006 inch, allows for lubrication and thermal expansion. This photo shows a typical arrangement.

Inner and outer wheel bearings

Typical hub and spindle, adjustable wheel bearing

They always design serviceable wheel bearing for use in pairs. The inner bearing is normally larger and carries most of the loads. The outer bearing balances the load and adds support. We must allow end play when we assemble and adjust the bearings. This end play, normally .004 to .006-inch, allows for lubrication and thermal expansion.

Properly adjusting a wheel bearing

how to check end play on an adjustable bearing 

We perform proper bearing adjustment with a dial indicator. The old method of tightening the nut and backing off a bit, is simply not accurate. Results like the ruined bearing pictured above often results. At AGCO we have found wheel bearing end play can be accurately set with a dial indicator.

The indicator base is attached to the brake rotor and the dial indicator tip rest on the end of the spindle. Pulling in and out on the rotor will show the bearing end play. The adjustment is made by tightening the spindle nut and normally held in place by a cotter pin.

Necessary bearing end play allows space for lubricant

Many spindles are double-drilled a slight degree off. This provides for fine tuning. If the cotter pin does not fit one hole, when adjustment is proper, the other hole may fit.  Packing bearings with synthetic wheel-bearing grease, installing new seals and properly adjusting them will provide almost unlimited life.  AGCO, it's the place to go!





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