Intermittent brake grind

[sunliner]

So I take my son's trailblazer to the store last night...as I'm pulling in, apply the brakes and there's a lovely sound like someone dragging a concrete block down the road. Goes away when brakes are off. So I figure time for new pads/rotors. I drove the truck today and brakes are perfectly quiet. It's been 7 years since last brake job, so I'm replacing, but just wondering how they could grind hellishly, then not at all next day?

 

[Reprise]

When brakes heat up, things expand. A pad wear indicator that's just starting to come into contact with the rotor will do so and be more noticeable when the brakes are hot. Vehicle is parked and brakes cool down - the wear indicator is farther away from the rotor and you don't hear them until they get hot again.

If not addressed, the pads will wear enough to where they'll be noisy sooner and sooner, eventually getting to the point where they're scraping 100% of the time (or nearly so).

In days of yore, if you caught it soon enough, you could have the rotors turned and only have to buy pads. Now, with rotors made ever-thinner, most people just replace them at every brake job, since it costs just as much to turn them on a lathe, now (if they're even thick enough), as it does to replace them outright.

 

[mrrsm]

The "Hellish Grinding Noise" can occur if the Brake Pad Material Adhesive separates from its Metal Shell and falls loose... allowing for the Brake Pedal to drop towards the floorboard while the instantaneous "Metal to Metal" contact creates all of the new noise:

 

[Mooseman]

Could have been a rock. Still worth a look.

 

[Maverick6587]

If you only ever heard it the one time. I would say a rock, like Mooseman. I would also check the dust plates. My dad's truck had a hellish grinding that you could hear from a block away. ended up being two horribly rusted dust plates that were about to fall off.