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My Renault Megane III Grandtour 1.5dCi 2010 has been annoying me for the past two winters. If left in cold weather overnight (which is almost always the case), I can hear a noise from the rear end when I brake. This persists for the first couple of kilometers when braking. It seems to go away after the thing heats up.

I always use my parking brake (handbrake) when leaving the car parked (and when I say always, I mean always). I suspect that may have something to do with it. I've been to the shop and they cleaned and tested the brakes. They assured me that everything is OK (and I trust their assurance, since the brakes perform as usual), but the noise did not go away. I also remember trying to not use the handbrake for a while last year, but it did not do much.

The parking brake did undergo maintenance during the time this has been happening - the "pulley wires" for both left and right side parking brake have been replaced due to wear, each a year apart (after a technical exam). But this has been happening since slightly prior to their replacement. It is more pronounced now, however. Note that I'm the second owner and the car was three years old when bought. This sound did not occur then - and the car was bought during winter time.

The sound is a deep "grinding" sound (which I'm having a hard time explaining in English). No squealing. It intensifies with more brake applied. It almost sounds like water flowing under pressure, like heating pipes - or hearing a neighbor above taking a shower (not the droplets, the moving water in the pipes).

A friend of mine suggested to try driving a couple of hundred meters with the parking brake partially active, but I'm not sure whether that is a smart idea. Is there anything else that could be done about it? It's just an annoyance, but still...I do feel some discomfort every time I start driving. I've driven several cars in my time, including a prior model of the Megane. None had such a problem.

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From the quick bit of research I've done, I don't think your car uses a combined drum and disc braking system on the rear - this means that pulling the hand brake while driving will only have a similar effect to pressing the foot brake in terms of what happens at the brake pad end. The noise you're hearing is likely to be a surface oxidation of the brake disc friction surface, exacerbated in winter by the world being a generally wetter place, salt on the roads etc.

It's not so much a "warming up" that causes the noise to recede after a few braking sessions, more a "polishing smooth" as the brake pad buffs the surface of the disc.

Modern cars feature brake balancer valves that split the braking effort so most of your pushing on the pedal goes to the front wheel. The rear brakes play a much more minor part in bringing a vehicle to a stop; braking at the rear wheels improves stability, particularly when cornering and braking, but as a result, the rear pads never really contact the disc very hard, so any oxidation that sets up isn't removed as effectively. Pulling on the handbrake may remove it faster, and won't really do any harm, but it's not a solution either

It's expected that the symptoms vary year on year, car on car, disc/pad combination on disc/pad combination. Even the way round you park your car can make a difference to how much rain splash it receives on the discs. All in, the shop should have found anything seriously wrong (like one pad is worn out and the bare metal on metal grinding is what you're hearing) but feel free to take it to another place for a second opinion. Most of my local shops will do a free brake check (and then recommend you only have 2.7 seconds life left in the pads when the material gets down to 5mm thick but.. )

TL/DR: It's probably slight oxidation of the discs, and nothing to worry about.

  • I did read about this and it is plausible that oxidation is the cause. But why does it "reset" every morning, even after going away entirely? And even in very dry, yet cold weather (salt perhaps only in form of dust). – predi Feb 9 '17 at 14:11
  • Tried the handbrake thing and this morning the noise was less noticeable, despite the fact that it rained last night. I guess if there is enough residue left, the issue "resets" faster an in a more dramatic manner. It is very likely oxidation. – predi Feb 10 '17 at 9:05
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The grinding noise could be caused by the brake pads dragging against the brake disks. This is not uncommon, see this question.

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