Rather, the bearing races — the bands or tracks in which the ball bearings sit and spin — begin to degrade, causing metal flakes to gunk up the grease. Regardless of the reason, a wheel ...

The other design has seals on both sides of the bearing, and one or two small holes in the surface of the outer race. Those holes allow grease pumped into the bearing flanges or housing ...

The balls, or rollers, are encased in a "cage" that supports the bearings, allowing them to rotate freely. The cage and rollers are held together inside a hardened metal ring called a "race." The seal ...