Rob Blumel

OK, so, when i bought my 2015 C4S, the seller generously offered to have the brakes done the day before i was to pick up the car. However, in the vein of no good deed going unpunished, the shop that did the work installed the rotors backwards, meaning on the wrong sides. When i picked up the car, the seller said the brakes were new, and the shop told him they’d just need to “bed in” before the pulsing would stop. Well, it hasn't.

Once i realized they were on the wrong sides, I swapped the rotors to their correct positions, but as I’d already put 1,000 miles on the car before I’d figured it out, I fear the damage had been done. Changing the rotors over made no difference; the brakes still shudder under normal braking. Hard braking is fine, light braking is fine, but for normal braking, like for slowing down from highway speeds to exit, the car shakes. A lot.

I’ve order and received new pads, and am set to install them, but I’m wondering now if the rotors aren’t warped. When I had the state safety inspection done, they measured the runout and said they were fine, so now I’m wondering if there might now be another problem causing this with which I’m as yet unfamiliar.

Thoughts? TIA

Rob

VII7

Installing backwards for a short time is unlikely to have damaged the rotors, they might have been defective to start with or they just warped.
Sounds like you'll need to spring for a new set.

Rob Blumel

yeah, I suspect the same. I’m going to throw on the new set of pads, and see how they work out. If the pulsing is immediately evident, I just order a new set of rotors. 🙄

VII7

Pads won't fix it might as well just get the rotors.

TX991.2

Did you try several hard stops at speed? There may be a bunch of deposits on the rotors that are causing the vibrations. Might as well try it before buying all new rotors…

asellus

Rotors don't warp, let's please stop this myth.

If bedding them in hard doesn't fix it -- we're talking 80-20 stops followed by cruising for a few minutes to cool them -- then your rotors are unevenly worn or have deposition that's fused to the point of needing to be turned or replaced.

Are they OEM rotors? Or some cheapos?

Rob Blumel

Rotors and pads are OEM Porsche and relatively new. Pads were new when whomever did the brakes incorrectly placed the rotors on the wrong sides.

I’ll bow to your superior Porsche knowledge vis-a-vis warpage, but I’ve seen rotors become “warped” - or, if you prefer, heat deformed - in the past. Overheated brakes, glowing rotors, etc. Use the terminology you prefer, they were trashed.

asellus

This isn't a Porsche-specific thing. Cast iron brake rotors do not bend. They crack. Centric has a good PDF explaining this, and I believe stoptech did a big article about it once upon a time.

But yes, the end is the same -- a trashed rotor, needing to be turned or replaced. New rotors will fix your problem, assuming (as cited in the pdf above, actually) your hub surface is flat and everything is torqued down evenly and correctly. I've experienced weird medium-force brake judder just as you describe on my Corvette because a wheel wasn't torqued just right, and the fix was just cracking loose and retorquing the wheels. Given the rotors were swapped to the correct corners and the problem persisted, that's unlikely to be the case here

Just doing a pad slap will more than likely not fix the problem, and could cause the pads to just persist the problem with new rotors. I'd replace the whole shebang, mostly out of fear of having to replace things twice.

Rob Blumel

indeed. Trashed is trashed, regardless of the reason. I suspected initially improper torque, as the rotors are a tight fit over the hub, but I dressed the hub surface and used anti-seize when I reinstalled them, ensuring they were fully seated with deadblow. Then I torqued the wheels. There no vibration when driving, so I know they’re seated.

I’ve got a set of slotted race rotors I’m going to on it for now while I see if these can be turned. If that’s not an option, I’ll just bite the bullet and replace them.

gents, this is a cautionary tale. If you’re having a shop do the work, please check that they actually did it right. The same shop that did the brakes totally botched the AWE Switchpath exhaust, requiring me to spend the better part of 6 hours repairing their work.

bkrantz

Did you check the run-out (lateral and radial) on the rotors?

Rob Blumel

I had Porsche do it and they said they were fine. I’m going to pull the wheels this am and inspect the rotors and pads.

I was actually just looking for where to buy a full set of rotors, but I’m striking out. Pelican pulls up a different PN each time, so I’ll just call them and see what they say.

Anyone else have a good source for these?

asellus

FCP Euro is the typical go-to for wear items like this.

RennListUser01

Any competent brake shop can measure the run out - if they are flat, great. If not flat the same shop can also turn them a bit - they will know how much.

Don't toss Porsche bucks at things if not needed.

CTDan

My 991.1 base had a pulse and a bad feel after a track weekend. I removed the wheels and used a green scratch pad and brake cleaner to clean the rotors. It wasn’t immediately “cured”, but was better and with use, eventually became normal.