mmarshall

I often get asked, by friends/colleagues, why their disc brakes sometimes have a scraping/grinding noise on initial use in the morning. To those unaccustomed to what causes this, and why, the noise can be disconcerting. One teen-age girl in my neighborhood thought she had a big problem that was going to require a lot of brake-work.

Fortunately, nothing of the kind. In most cases (including hers), that initial grinding/scraping noise occurs after wet or damp conditions when the brake rotors have built up a thin coating of rust on them. This could include a damp/foggy night, rainy/wet weather, or simply after you have taken some time to hand-wash your car with a hose (as I do). When this happens (and it is a very common occurence, especially if the car sits for awhile), the rotors will have a layer of orangish-brown rust on them, looking something like this:



In most cases, simply using the brakes for a couple of pedal-applications (say within the first half-mile or so), will quickly wear the rust layer off and restore the brakes to their normal quietness. It's better to use the pedal gently then with hard-applications, as then the rust-particles will wear off with less chance of affecting the metal-finish on the rotors.

Most production cars, of course, use steel rotors (vented or unvented), which are prone to this condition sooner or later in almost any damp or wet condition, although a few high-performance sports cars and exotics use expensive carbon/ceramic rotors which don't rust or corrode (they also resist warping from heat build-up much better than even ventilated steel rotors).


Of course, if you do continue to have rotor or scraping noises with brake use after the rust layer is quickly worn off, then you have another problem that needs to be looked at....such as a glazing on the brake pads or the incorrect-type brake pads for the vehicle. Or, in an absolute worst-case scenario, if a high-pitched noise also occurs, the pads may be worn out and the brake-wear indicators touching what are called the "Screechers".....which is a warning sound that a brake job is needed immediately (ASAP) to avoid rotor-damage or replacement from metal-to-metal scoring from the calipers. But, unless the brakes have been neglected or not inspected for a long time, that will not usually be the case.

edgeucated

iTrader: (4)

My car does it and I have came to the same conclusion about the rust because it only happened for a bit after the car sat for a while.

Funny thing is it didn't start to happen till I replaced my OEM rotors with new OEM rotors purchased from the dealership. I wonder why my original OEM rotors didn't squeak in the morning and my new ones do?

UDel

I remember I visited my parents for a couple months when I was younger and left my car sitting. When I came back it started up but I thought it needed new brakes it was making such a horrible sound. My friend who is a mechanic said it will go away the more you drive it and it did. Rust and the tires being slightly out of round from sitting too long will definitely get your attention when you first start driving it.

Hoovey689

iTrader: (16)

Mine do it every time I wash the car. I simply drive down the street, slam on the brakes and head back home

mmarshall

Were the original rotors made of stainless steel...or don't you know? (I'm going to assume that they weren't the carbon-ceramic rotors generally found only on exotics and ultra-high-erformance cars) Stainless steel, of course, is far more resistant to corrosion/rust than ordinary or untreated steel. Not being a mechanic or technician myself, I don't have, or know of, a specific list of production vehicles that use OEM stainless-steel rotors.

From what you describe, it sounds to me like that is at least one possiblilty...the first set of OEM rotors you had were either stainless steel or given special anti-corrosion treatments at the factory, then, most likely due to cost-cutting, the manufacturer switching later on to less-expensive ordinary-steel ones, which then started to rust in damp conditions and cause that scraping noise on initial-use.

You can see some other rotor cost-cutting measures in a lot of vehicles simply by comparing the front-vs.-rear brakes. On vehicles with 4-wheel discs, many of them not only have larger rotors up front, but those rotors are usually vented, and the front brakes, on average, have more pistons than the rear brakes. By contrast, rear-disc brakes often have smaller-diameter, unvented rotors and fewer pistons, though some rear rotors on high-performance cars are vented. Manufacturers usually justify this discrepancy by pointing out the inherent forward weight-transfer of a vehicle when braking, placing more of a load on the front brakes and forcing them to do more of the work (and some of that, of course, is goverened by the brake proportioning-valves that distribute front/rear brake-line pressure). But excuses or not, it is a fact that the rear brakes on the majority of today's cars are cheaper to produce than the front brakes. Then, of course, some enrtry-level compacts/subcompacts don't have disc-brakes at all in back, but still rely on drums.

Lil4X

When we were kids, a friend's bike brakes began to squeal as the rubber brake blocks hardened. He oiled them. Wonder whatever became of that guy??

Was likely removed from a solid roadside object with a paint scraper years ago.

mmarshall

Yes...in most cases, the scraping noise with wet/rusty rotors will disappear after a couple of pedal-applications (about 3 or 4 in my case) and maybe a quarter or half-mile. If it doesn't, of course, then you have other problems with the pads or rotors which need to be looked at.

I wouldn't just slam on the brakes like that, though, Hoovey. Like I mentioned above, doing so gently will dissipate the rust better, prevent it from messing up the metal-finish on the rotors, and help prevent rotor warping or uneven-wear spots.

mmarshall

I forgot to add the obvious, of course.........that this could be an ongoing problem (among others) for vehicles that spend a lot of time at the beach or in coastal areas exposed to damp salty air and/or salt-spray.

mmarshall

That sounds like the kind of stuff we used to watch, years ago, on the Three Stooges....remember them?

Kira X

iTrader: (24)

My cars only make noise after I've washed the car. This explains why they make that sound.

mmarshall

Don't be surprised if you also sometimes get it after a rain....although part of that also depends on how the wheels are designed

Kira X

iTrader: (24)

I've actually never heard the sound in the rain yet.

Do drum brakes make the same noise? I typically drive my Saturn SL2 when it's raining hard but I never heard the brakes make the sound like my other cars do.

mmarshall

In general, drums won't make the same noise, under the same circumstances, because the inside surface of the drum (where the brake-linings actually rub on them) is partially shielded from water by the metal casing of the drum itself. The inside of drum brakes can get wet if you drive them through a deep enough puddle, but the wet linings/drums quickly dry out from several applications, though there will be noticeable fade/loss of rear-brake performance as they do dry out. But, in general, the water doesn't stay in the drums long enough to rust the inside of them unless you park the car immediately (or soon after) driving through deep water without drying them out.

If drums-brakes, with pedal-use, do make a scraping noise after drying out (or not getting wet in the first place), then the linings may be worn out, and the metal backing-shoes contacting the inside of the drum. As with the "screechers" on disc-brakes that I described earlier, a brake-job then has to be done immediately to keep from scoring the drums and/or requiring refinishing or replacement.

Even in the rain, your Saturn's disc brakes shouldn't make the noise either if you are actually driving them in the rain, using the brakes, and the rotors don't get a chance to rust because of pad-contact. They tend rust after exposure to water or damp conditions if you weren't actually using the brakes at the time to prevent it.