Spalling (was: Rusted on disc brakes)

It's when the hardened surface layer of the bearing race splits off the tougher backing layer. Thereagain it normally only happens on a bearing that was on the way out anyway.

In message , Microstar writes

But as spalling affects the races, you are more likely to encounter it if the shock loading is applied radially and not 90 deg to the race as you would do when hitting the disc from the rear.

Quite. I have never known of bearings being damaged by hitting a disc from behind.

When you think of the force a bearing is subjected to when taking a bend at

The problem is the fact that it is a high shock load. Wheel bearings do not normally experience high shock loads due to the fact that there is a pneumatic tyre between them and the road. Many vehicle manufacturers specifically warn against hammering off the discs, still, if its your own car you do what you want.

Why would you hit a disc from behind anyway? It's quite difficult and if you want to remove it one solid whack on the front middle, where the wheel bolts on, will shift it quite nicely. It may or may not damage the wheel bearing - I doubt it because they take a hell of a lot of punishment in use - but if the alternative is no brakes it's hardly worth worrying about. Trying to force it off would probably do more damage than a sharp shock to break it loose.

You didn't see the photos then? No amount of hitting in any direction was going to shift them.

Dan Buchan mumbled:

You've not tried getting 'em off a Renault Trafic! Took me ages (and I'm no weakling) with a lump hammer.