Aluminum brake calipers (automotive)

Brake fade from caliper creep at temperature. Used to show that the same aluminum-temperature problem afflicts ground vehicles.

The problem with the heat treatable is they can start to degrade at fairly low temperatures. The supersonic transport Concorde was not limited on speed; it was limited on the skin temperature of the heat-treatable aluminum alloys. They would start to over-age and you'd lose your precipitation hardening. They actually had sensors on the surface that would measure the temperature, and the colder it was up there, at whatever altitude you were, the faster you could go. But you didn't want to destroy your aircraft by overheating the aluminum. The same type of thing — they've just started coming out with aluminum in automotive brakes. The first real problem of trying to use it for calipers — not the drum but the caliper that holds the brake pads — was they would creep. You hit your brakes hard, you get too much temperature, and all of a sudden the caliper holding the brake pads starts to splay out, and you no longer have any pressure on your brakes. It's called brake fade, and it's not a good thing. They fixed some of that.

Attempted aluminum brake caliper housings ~1989 failed due to creep above 200°F (brake fade). Took ~25 years to develop alloys that worked. Tom's anchor case for the sprung-weight-value pyramid.

So 25 years ago they tried to use aluminum calipers for the brakes on cars. You know, you've got disc brakes. They don't try to use aluminum for the disc in the disc brake — that's made out of cast iron, for reasons that have to do with the wear resistance and frictional properties of cast iron. They wanted to make just the brake pad housing — the housing was made out of ductile iron. If they could make that out of aluminum they could take 15 or 20 pounds off the sprung weight of the vehicle, which is worth more than two dollars a pound — it might be worth ten or twenty dollars a pound. Well, they tried, and the problem was, brakes heat up if you use them really hard. Some of these aluminum alloys aren't much good above 200 degrees Fahrenheit — they start to creep. If your brakes start to creep, they call that fade. That means if you slam your brakes on hard two or three times, or you're coming down from Berthoud Pass on Interstate 80 [70], heading from Salt Lake into Denver — anybody know that area? Colorado, big long downward slope. Got lots of turn-offs for the trucks because they go rolling off the mountain — probably lose 20 trucks a year just going over the edge. The guy just opens the door and jumps out and lets his car go down the mountain, and they have these ramps where they can slow down. The Eisenhower Tunnel — you've got like 20 miles of just coming down the Rocky Mountains at about six percent grade. If your brakes fade, then they no longer are braking. Not a good thing. So aluminum brakes didn't work. Although they've developed new ones — it took them 25 years — I've read that some of the newer cars have aluminum brake housings. Because of the creep problem, they had to overcome that, and it took them a couple of decades to figure out what the right alloy would be.