Adjusting serviceable wheel bearings is something that normally does not get a lot of thought. Even many experienced technicians do not adjust them properly. Premature failure is the normal result and severe damage can occur.
This cross section shows a typical roller type wheel bearing. The red area, between the rollers and the races are the space where lubricant exist.
As the bearings roll, heat is generated and the rollers expand slightly. This expansion takes up room, where the lubricant must fit. If there is not enough space, the lubricant will be forced out. When this happens the rollers contact the races and damage occurs quickly. This bearing was improperly adjusted, only 5,000 miles before this picture was taken.
The bearing has been destroyed. Metal flakes and damage to the rollers resulted 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.
The old method of tightening the nut and backing off a bit, is simply not very accurate. Results like the ruined bearing pictured above often result. At AGCO we have found wheel bearing end play can be accurately set with a dial indicator, set up as in this photo.
The indicator base is attached to the 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.
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!
