mgordon18

My rear brakes are squealing when I'm not pressing the brake pedal. Once I press the brake (even just a little), the squealing stops. It began after 2 days of track time a few weeks ago. The pads do need replacing - they're at about 3 or 4mm - so I'm planning on doing that, but I've never had brakes squeal when NOT on them before. It's loudest at low speeds, like 5-10mph, and tends to dissipate as speed increases. It seems to be gone at 35mph, but it could be being drowned out by other engine/road sounds.

Any ideas what it could be? Maybe a stuck brake piston?

Thanks in advance.

tstafford

StormRune

Since you have an S with torque vectoring, when driving sportily in curves the car will apply the inside rear brake to help the car turn in better. Is this possibly when you are hearing it?

Jay-S

I've been dealing with this issue for over a year. Exact same circumstances as you.

I gave up taking it in for awhile but it is really annoying. Six trips to dealer so far:

1. Replaced pads and rotors
2. Flushed brake fluid
3. Thoroughly cleaned the brake hardware
4. Replaced brake hardware (bolts if I remember correctly)
5. Could not replicate
6. Cleaned all contacts surfaces, resurfaced rotors, chamfered pads, replaced more hardware

This last time is the most promising, but it'll be some time before I believe that I'm out of the woods.

okbarnett

I would start with washing out all the brake suspension parts

mgordon18

I'm going to to that myself, once the new pads arrive at my house.

mgordon18

It's most noticeable at the lowest of speeds, like when I'm pulling into my garage and stopping for stop signs and such. PTV is not engaged at that point.

mgordon18

Hi Jay,

Did it first occur after a track day? Have you tried getting the caliper(s) rebuilt? I read somewhere that sometimes brake pistons stick and don't retract properly. Has that come up? Has any of the above work been done under warranty?

Thanks.

bkrantz

This sounds likely. The caliper seals have a shape that is designed to retract the piston a small amount after each brake application. If this does not happen, the pad can drag on the disk--not good, since the brakes can overheat.

alz

To understand a bit more, do you have brake pads that squeal when you brake (e.g. Pagids)? Or are you saying the standard brake pads that never squealed before are now squealing. Also is it a fairly loud squealing (equivalent to when you brake)? Or just a little squeaking as you come to a halt.

I had a bit of squeaking on my '13 C2S after I installed Pagids. Similar circumstance in that the squeaking didn't show up until after the first track day. It went away after the next track day and I haven't thought about it since - but not sure if this is similar to your case or not.

mgordon18

These are stock pads that otherwise do not squeal. This is pretty loud squealing when NOT on the brakes. It squeals when coasting or on the throttle at low speed. The lower the speed, the louder the squeal until about 35mph when it's finally too faint to hear. To me, it doesn't sound like the same kind of squealing that comes from track-oriented pads like Pagids. it's higher pitched and more annoying! As soon as I actually touch the brake pedal the squealing stops.

alz

Got it, that's quite different. Any chance one of your pads has entirely worn through and it's metal to metal ? Might be an inside pad that you can't see.

Jay-S

There is a reason that a track day would cause this. The brake fluid heats up and an air bubble gets in the system. According to the mechanics working on my car, this is a known issue on certain Cayennes and the symptoms are the same. They said they had not seen it on 911s though.

This was ruled out on my car because they did a brake fluid flush and the issue persisted.

Jay-S

Nope!

mgordon18

I guess that's possible - I'll see when I get in there next weekend. But if this were the case, wouldn't it scream like a banshee when I press the brake pedal? When I do that, the squeal goes away.