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Discussion Starter · #1 · (Edited)
Car is a 981 CGTS 2016 M/T with now just under 7000km on the clock. Owned it from new (January -16). Until now, no issues whatsoever.

Problem: At very low speeds, pedestrian even, there is a very faint sound just as I start to apply the brake. It is very similar to the sound the rear parking sensors make as you go into R, to make you aware they're there and working (I guess). But this sound is much weaker, and shorter. There is no warning anywhere on the dash or any stored messages/errors.

I can replicate it whenever I want, but only at very low speeds, probably because it's not detectable as soon as some road noise comes in.

I first thought brake fluid level could be low and the warning just triggered because level sensor dropped when fluid goes out into the system. But the level is fine and also, the sound doesn't come if I reverse and apply brake, just when going forward...

The car feels its normal, wonderful self in all other driving conditions. I could maybe ignore this but A: something has changed and B: I have a track day coming up in two weeks and I do not want to have a bigger issue just before or even at the track...

I do not think it's a chip or stone between the disc and brake shroud because the sound is only there when pressing the brake. Also, the character of the sound is more of a "tone" (like a warning signal, "ding!") than a "squeak". If you see what I mean.

Any ideas? Thanks!
 

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Stock pads? I've had race pads make an almost honking noise when cold. Usually re-bedding takes care of it for awhile. Before taking it on track though best to get a qualified mechanic to inspect the brakes if you have any doubt at all.
 

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My brakes make a slight 'honk' or 'squeak' sound sometime when I'm backing out of the garage... I don't drive the car every day, mostly just on the weekends, so it just sits in the garage all week. It seems to happen just as the brakes grab and the car comes to a complete stop. Not sure if same noise as OP, but if it's the same noise as mine it's probably not a big deal.

I've always attributed it to the angle of my driveway combined with the pads and rotors being cold. The noise goes away after a few minutes of driving, presumably because everything is warmed up... If you think it's a problem, and it's easily repeatable, have the dealer look at it.
 

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Discussion Starter · #4 ·
Thanks all,

Pads and rotors checked - no damages. Since the sound comes as soon as I start some travel on the pedal, but before there's any retardation (i.e. the pads hit the rotors) I don't think there is something at the wheels.


I did go to my P-dealer yesterday and had the very helpful service manager plus a technician to take it for a spin. They heard the sound, they got it on film, will send it to the Swedish importer to create a warranty issue. They think it's the booster making the noise. On my question why it doesn't come when standing still or reversing, they say the booster work differently in different driving modes. Haven't heard that before, but what do I know ;)


So, we have booked a slot for changing booster, end of September. However, the importer has to approve the warranty issue and that is a process we will see the outcome of in a couple of weeks.
 

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I don't know what a booster is. I didn't realize you said it happens before the brake pads make contact with the rotors.

Sounds like you'r in good hands with the dealer though. Let us know what the problem ended up being.
 

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Discussion Starter · #6 ·
Yep, I'll report back. Brake booster, or "servo", is the big round thing just in front of the firewall on the driver's side, when you lift the big plastic cover to for instance check brake fluid or charge battery. It typically runs on vacuum to enhance the force from your leg out into the brake system so that we don't have to press extremely hard to achieve proper force on the pads. They have been around for a while but as I said, I haven't heard they can run in different modes. You'll learn something new every day :)
 
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Vacuum boost doesn't change with driving modes on any car I've ever driven and owned, including the 2 981 GTSs in my garage. What dealer was most likely referring to is in sport+ (and maybe sport; can't remember), the pads get closer to the rotors, basically touching them, to minimize reaction time. And also when it rains (probably with rain sensing option, or maybe just when wipers are cycled; can't remember either), pads actually apply some pressure to the rotors to heat them up and dry them. Maybe that's what's happening; who knows. You'd have to put the car on the air and try to move the wheels; they should move freely, but it's normal to hear the pads rubbing against the rotors. But all of that is a function of the braking (ABS) module, not the brake booster. Besides, you'd immediately feel if boost changed, like when you drive a different car and look like a rookie the first time you brake, apparently slamming on the brakes, when you were just applying the pressure you were used to from the previous car. Or the opposite, feeling the car doesn't stop, and need to apply a lot more pressure. At any rate, if you checked the rear calipers and are no pebbles lodged inside the pad cavity, and wheels move freely, then probably nothing wrong, especially if you don't feel a pulsation when braking, that could indicate a warped rotor, or heavy deposits. But if brake pedal feels firm and doesn't pulsate when braking, your rotors are fine. You can also check the pads, to make sure they're wearing evenly, especially the inside ones. Oh, and also make sure your brake fluid is not more than 2 years old from build date. If it is, replace it. I'd make sure something is actually wrong with the ABS module before messing with your car. That tech didn't give me too much confidence, but maybe he was referring to the ABS module all along, since it can be a pressure 'booster';). Good luck.
 

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Discussion Starter · #8 ·
Thanks a lot for input. Interesting. I agree that I was a bit surprised that the brake booster would have different "modes". Never heard of it and I have worked in automotive product development since 1994... However, I might have been a bit unclear in my first post, the guy didn't say "modes" as such, he said the booster works differently depending on whether the car stands still, goes forward or reversing. So, he clearly didn't mean the drive modes, just different operating modes. Maybe the vacuum is increased once the car is moving (for some reason). Once the summer holidays are over here I will definitely discuss this with colleagues who know more than me about brake systems.

But the ABS module idea is interesting. I will either way have discussions with the dealer before the car goes in (the matter of warranty etc) and will put that forward.

(Just a quick comment on posting same Q on two forums - I have no idea if everyone on one forum is also member on the other, I would assume not, and therefore posting on two increases the chance of finding a solution. But I might be wrong...)
 

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Fun to read about all the sophistication in the 981. My 914 has none of it, no ABS, no booster!! If only it had no rust, too! You have to get used to really pressing on its pedal, though. A small woman would have trouble. Completely different from my '61 Olds, where the slightest touch would put your teeth through the windshield.


Sent from my iPhone using Tapatalk Pro
 

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Discussion Starter · #10 ·
So, an update in this matter: Car came back from dealer on Wed this week. The brake booster was changed, I was shown the old one that came out of the car. However, the service manager admitted that he could still hear the sound... But he wanted me to use the car for a bit and make my mind up about it. It took me about not even 20 m to realize the brake booster change had done nothing at all to address the issue... So any input is welcome, to what might cause this. Also if any 981 owner is experiencing the same thing. Since it is a very faint (but still noticable) noise, it is during parking maneuvers and driving very slow speeds that I can hear it, like typically slowing down for a speed bump from 30->10km/h. I'm sure it is there also at higher speeds but with everything else then going on, I can't distinguish it then.

It can't be only my car that has this phenomena... :)
 
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So, an update in this matter: Car came back from dealer on Wed this week. The brake booster was changed, I was shown the old one that came out of the car. However, the service manager admitted that he could still hear the sound... But he wanted me to use the car for a bit and make my mind up about it. It took me about not even 20 m to realize the brake booster change had done nothing at all to address the issue... So any input is welcome, to what might cause this. Also if any 981 owner is experiencing the same thing. Since it is a very faint (but still noticable) noise, it is during parking maneuvers and driving very slow speeds that I can hear it, like typically slowing down for a speed bump from 30->10km/h. I'm sure it is there also at higher speeds but with everything else then going on, I can't distinguish it then.

It can't be only my car that has this phenomena... :)
Since you said it was caught on video could you post a clip so we could hear it.
 

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It can't be only my car that has this phenomena... :)
Maybe it's all of them;). Have you driven another GTS??? But yes, unless you post a video where the noise you're complaining about is clearly heard, the only way to find out is either driving somebody else's car, or let another GTS owner drive yours (or ride shotgun). But for what you're saying, doesn't sound like anything worth worrying, to be honest. My car is PDK, but the brakes shouldn't be any different. The only thing I HATE about modern brakes with 'brake assist' is that when you're braking moderately hard, the stupid system thinks brakes harder than you want, and takes a fraction of a second to release brake pressure after you do with your foot. It's quite annoying, but no strange noises. Noises at very slow speeds could be the cold brakes; quite common with performance brakes. After you post the video we can comment.
 
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