Can the brake rotor go bad without the pad going bad?

With the rotors, again, there’s a new thickness, and a service limit, specd in the Repair Manual, and that’s likely (possibly?) what they’re on about, with this “30 percent”. It’s typically measured with a micrometer.

 

I'm not sure if I've ever heard of a brake rotor getting worn to anywhere near its service limit thickness just through wear while using the brakes. It's usually more of a consideration for how many times you can stick it on a lathe and resurface it.

Though sometimes, in a case of severe rusting, it's worth asking the machinist "is this rust even deeper than the maximum cut you can make?"

I did have a Mazda years ago that was my first experience where the factory pads seemed to be made out of something not much softer than the rotors. That car pretty much did need rotors every time it needed pads. I don't remember it as uniformly wearing down near the service limit, but they would get all gouged up, so by the time you could cut a smooth surface on it again, there you were.

 

We had one Accord with the front rotors worn down below service limit. It also "ate" pads, pretty much every 30K kms. I suspect sticking caliper piston, never got on it though. Driver's side rotor finally cracked, a radial fracture. Car sounded like it had a broken back every time you applied the brakes.

Took it to dealership, described the problem. Half an hour or so later I got a call: your car's ready, there was no problems...

I was relieved, for a split second. Then common sense kicked in, and I told them to take another look. Hung up. Thought a minute. Emailed the Service Manager. About another half hour passed, and the Service Manager called. He had the (obviously cracked) rotor on his desk, apologised. He was the one ray of light at that place.