Scraping noise from rear disc brakes

Horizon81

Wondering if any mechanics can shed some light...

Car is a Honda Civic with rear disc brakes, but I've heard the noise on several other cars, all with rear disc brakes in common e.g. Toyota Celica, Subaru Impreza.

The noise comes from the rear of the car, whilst the car is being driven. If you're driving the car, you can only hear it with the window down when driving slowly (and it's amplified significantly when driving past parked cars, I suppose they must bounce the noise back). If you're a pedestrian, and a car with the problem drives past then it's clearly audible. It's a rotational (but quite light) metal-on-metal sound, consistent with the speed of the vehicle. Sounds like something is feintly catching or scraping. When braking, the noise fades/disappears.

I've tried braking hard to clear any surface rust (there isn't any on the faces of the discs) and I've also tried applying the handbrake lightly whilst driving, all of which has had no effect on this noise. I'd say its more pronounced when the car (and so the brakes) is cold but it's there all the time. Plenty life left on the pads so it won't be the metal tell-tale for when the pads are nearly shot, plus the noise fades upon braking. Any ideas???

JUNIOR

I'm no mechanic , but i do own a civic;)

How long have your brake pads been on ?

I'm pretty sure they need replacing , i had the same problem at the front .

its not the pads that are grinding , but a small peice of metal thats grinds to let you know you need to replace pads .

Take it to your local (private) garage to get em checked out

J

Stigy

Sounds like it's either a backplate rubbing against the disc, or the pads are very low and the sound you hear is a warning system that lets you know they're low. The sound usually disappears when you push the brake pedal if it's the latter, but it might be slightly different on rear brakes as only around a quarter of braking occurs at the rear of the car. These warning markers if you like, resemble small tabs that are metal, and start to rub the discs when the pad becomes too low. Quite an archaic way of warning you, but I'm not sure how old the car is, plus Japanese manufacturers were still using this system until very recently anyway.

Hammyman

It could be the crud that builds up on the outside edge of the disc catching the caliper.

Horizon81

You could well be right Hammyman. It certainly sounds the most logical explanation. They've made this noise for months and if it had been the pad indicator then surely the discs would be scored (which they aren't) plus it's been to the dealers lately and they do a visual safety check and I'm sure they'd let me know if brakes needed replacing (had fronts done only a few months ago). I'll scrape off the loose rust when I get the chance - screwdriver and sandpaper should do the trick!