Rebuilding a caliper from a Birel kart. This is a 125X4, 4 piston with 4 pads. Each piston has a magnet to retain the pad. I cleaned them in an ultrasonic cleaner with water and degreaser. One broke while cleaning and 2 more broke when the snapped together after cleaning. I’ve never seen anything so fragile. No big deal till I found out they are $16 each, WTH!
Could the ultrasonic cleaner have done this?
Maybe. Depends on how the magnets were made. If they were compacted magnetic material held together with some sort of binder, then the degreaser could have dissolved the binder or at least weakened it causing them to break.
The way they cracked and crumbled that wouldn’t surprise me that they are made that way. I would hope that since these are part of the brakes they would have spec’d an item that can withstand cleaning chemicals. Note to self - don’t use degreaser on the magnets!
Having seen chipped and broken magnets over the years . . .
"Neodymium magnets are made of a hard, brittle material. Despite being made of metal, and the shiny, metallic appearance of their nickel plating, they are not as durable as steel.
Neodymium magnets can peel, chip, crack or shatter if allowed to slam together. Eye protection should be worn when handling magnets, since shattering magnets can launch small pieces at great speeds.
Neodymium magnets are not easily drilled or machined."
I also have done some web searching on magnets, and I’m not sure these are neodymium. Apparently neodymium has a low temp (80*c) working temperature, losing magnetism that may or may not return when cooled. I am certain brake calipers get warmer than that. However, I have no way of determining what the material is, but as you link points out, they are fragile. The Birel magnets are not nickel plated either. Thanks for the info Mike.