boxsterisgood

Update: there are also scratches/grooves around the bottom of the rotor hub(the center hub not the rotor surface). Both two rear rotor hubs have such dark black scratches/grooves. Is it possible the pads are not original? I forgot to take pictures of the back of the pads.

Hi guys, I would very much like to hear your inputs and guidance on my brake pads. Here is the timeline of everything I know regarding the brakes of my 981S.
2021-Feb I bought this car from Carmax and I had never heard any grinding or squeak noise even when the top was open.
2021-Mar A couple days after I bought the car, I made an appointment for PPI with a very popular and famous local indy shop. They made a thorough inspection for $350 and the report ended up with "excellent". However, right after I took the car out from the indy shop, I heard very very loud squeak/grinding noise. I called the indy shop right away and they told me it is normal because the brake is pretty new(brake pad 95%).
2021-Dec It has been longer than six months and I have been hearing the squeak until now. I believe it is not supposed to be so because new brake pads shouldn't grind for such long. So I decide to figure it out myself. I jacked up my car, and checked all four brake pads and it turns out that there are deep and regular scratches to both my rear brake pads.

Some more information: both rear pads, four in total, have scratches. The scratches are multiple and parallel. The pads are all worn evenly, both vertically to the rotor disk and also similar thickness(there is only a little difference in thickness).

Here are what I would like to learn:
1. What would be the potential root cause? Because both rear pads have this issue, it shouldn't be some random rock or gravel. Moreover, because the scratches are not only one but three to five parallel scratches, it shouldn't be rocks as well. One guess I have right now is the caliper might not align very well?
2. Is it possible something happened during the PPI? I heard zero grinding for a couple of days before I turned it in for PPI. I called the shop again but they said it's been so long and they couldn't recall. They asked me to make an appointment for inspection but I declined. I don't want to mess up with them because they lose my trust, at least for now.
3. Do I need to replace both rear pads even if they have 90% thickness right now?

Thank you guys.

Updated: I uploaded more images regarding the rotor in Imgur [here](https://imgur.com/a/PsgwM7o) because they exceed the max attachment limit in rennlist.

saabin

Is your only complaint the noise? Braking performance is OK otherwise?

What's the condition of the rotors?

Seeing as how they rear pads are at 95% (new), my guess is carmax just threw on a cheap set of pads prior to selling ?

You could replace the rear pads assuming the rotors are OK and not grooved in any way. I don't think the PPI had anything to do with it.

Diamond Dave

Would need to see the rotors . I think I would just try new quality pads next.

thecajunboy

Possible that a better guess at what's going on if you could provide more information. No way to discern which pad came from which location. That makes it impossible (for me at least) to tell if the grooves are on the leading or trailing edge of each pad. Or even if the inners and outers have similar wear pattern. Was the vehicle left out in the rain or washed at the indy shop? Maybe the rotors rusted over and then they did a hard stop driving test under those conditions? I love mysteries like this, but a little more info would help.

MMaynard

Would like to see the rotors, also with the car on jacks do you hear any noise spinning the wheels

boxsterisgood

Yes, noise is the only complaint. Performance-wise everything is ok.

I just uploaded quite a few images of the rotors in Imgur because of size limit here. The link is added to the bottom of the post.

boxsterisgood

I just updated the main post with a directory of rotor images. Thank you.

boxsterisgood

I just updated the main post with a directory of rotor images. I used quickjack to jack up the car and I didn't notice any spinning noise. I indeed put handbrake on and I don't know if that prevent the rear wheels from spinning if there is a potential issue?

boxsterisgood

I just updated the main post with a directory of rotor images. I really like your attitude and patience towards different mysterious problems. I didn't take many pictures while I took off the wheel and brake pads so it is indeed hard to tell if the grooves are leading or trailing. Well, if I am shameless to jump a step further, what if we know they are leading grooves? What if they are indeed trailing grooves and the probable issue would be?

The car was kept in the garage during PPI and I don't know if they washed it.

Kitc2246

After looking at the rotors they look newer than the pads. Carmax may have put on new rotors and kept the pads. You can go through a "bedding process" that might improve the squeak sound. FCPEuro is a good source and has a Lifetime Warranty. There are good OEM equivalent rotors and pads, but if you want excellent braking with little or no squeak, you can't go wrong with Porsche OEM rotors and pads. If you DE or track the car you will need to upgrade the pads and eventually the rotors.

TMc993

I'm thinking that the damage is occurring because the leading edges of the pads are flaking or fracturing at the point where the friction surface meets the edge of the chamfer on the pad. The noise would be the bits of pad material getting trapped between the pad and rotor. Do you know if the pads are Porsche, OEM or aftermarket?

EDIT: As mentioned above, this could be caused by rotors being in poor condition.

badabing

I think someone pad slapped it on old rotors before trading/selling to carmax.

Then upon inspecting the car, carmax probably measured the rotors to be below wear spec and replaced them but kept the pads since they were new.

Also, you didn't mention anything about the pad dampers that are stuck to the pads which means either they are missing or were reused in which case they aren't effective because the adhesive is cooked.

Put a new set of pads and pad dampers.

thecajunboy

Can't say that my rotors look much different from yours. I do get noise after a was if the rotors rust over, but the noise goes away after scrubbing them clean. They don't make noise like that again until I wash it ans the rust over again. Knowing the orientation that the pads were installed (trailing or leading edge being affected more) might cause you to consider a piston sticking, and if that were the case you would only know which piston to look at. Assuming here that the wear across all pads indicated the same wear direction. Not sure if that is all worth much, but if a caliper rebuild is in order, then it would be wise to do all the pistons,seals, etc. I thought it may have been possible there could be corrosion/rust in some of the vent holes on the rotors that could have caused the issue but the photos prove that invalid. If you're going to DIY this, I'd start by replacing the cheapest component first.

9eight7

It looks like there are some deep scratches on your rotors. My guess is the leading edge of your pad chunked off and got stuck between the pad and rotor which is why you hear the noise. Is there a part number on the back plate of your pad?

boxsterisgood

What is a bedding process and can it be done DIY? Regardless, thank you for providing valuable information and I used FCPEuro a couple years ago when I replaced my valve gasket for an E93. I am ordering new rear pads from them right now.

By the way, I updated the main post because I noticed some scratches around the bottom of the rotor center hub. That might be a good indicator of your guess: Carmax replaced new rotors but kept the pads.

Thank you so much for your time.