Piston Slap: That Gritty Feeling in Your Brakes?

TTAC Commentator 1500cc writes:

Hi Sajeev,

I have an odd problem with the brakes on my 2014 Cadillac ATS 2.0 AWD. It has 35k miles on the clock and the Brembo brakes up front. It started happening last spring: when I’d apply the brakes I’d feel (more so than hear) a grinding or gritty feeling through the brake pedal. The odd part was that the brakes were nice and smooth when cold, and only started to act up after I drove a little bit and the brakes warmed up. Also, it only seemed to do this in the final few feet of a stop, say from 10 mph down to zero (or maybe I just couldn’t detect it at higher speeds). The grinding was proportionate to how hard I pressed on the pedal, but pulsed a bit with the rotation of the wheels as if the rotors were warped.

So the first thing I did was pull the front wheels (for some reason it felt like it was coming from the front) and while the rotors were good and rusty, there was lots of meat left on both the rotors and pads. But just to be sure, I installed new front rotors and pads (a shop said the rotors were too gnarly to turn). Didn’t help. Okay, let’s look at the rears, then. They actually were worn to the point of needing replacement, so on went new pads and rotors there, too. But the problem is unchanged, including the pulsing sensation.

Searching the internet, I’ve seen a few forum threads with pretty much the exact symptoms (fine when cold, grindy/gritty when warm) on everything from Explorers to pickups to Porsches. Unfortunately I couldn’t find one thread that actually had the answer. There were some left-field suggestions like an overfilled master cylinder (I took an ounce or so out of mine just to be sure), but nothing fixed it. What could it be?

Read more
  • Dennis Howerton Nice article, Cory. Makes me wish I had bought Festivas when they were being produced. Kia made them until the line was discontinued, but Kia evidently used some of the technology to make the Rio. Pictures of the interior look a lot like my Rio's interior, and the 1.5 liter engine is from Mazda while Ford made the automatic transmission in the used 2002 Rio I've been driving since 2006. I might add the Rio is also an excellent subcompact people mover.
  • Sgeffe Bronco looks with JLR “reliability!”What’s not to like?!
  • FreedMike Back in the '70s, the one thing keeping consumers from buying more Datsuns was styling - these guys were bringing over some of the ugliest product imaginable. Remember the F10? As hard as I try to blot that rolling aberration from my memory, it comes back. So the name change to Nissan made sense, and happened right as they started bringing over good-looking product (like the Maxima that will be featured in this series). They made a pretty clean break.
  • Flowerplough Liability - Autonomous vehicles must be programmed to make life-ending decisions, and who wants to risk that? Hit the moose or dive into the steep grassy ditch? Ram the sudden pile up that is occurring mere feet in front of the bumper or scan the oncoming lane and swing left? Ram the rogue machine that suddenly swung into my lane, head on, or hop up onto the sidewalk and maybe bump a pedestrian? With no driver involved, Ford/Volkswagen or GM or whomever will bear full responsibility and, in America, be ambulance-chaser sued into bankruptcy and extinction in well under a decade. Or maybe the yuge corporations will get special, good-faith, immunity laws, nation-wide? Yeah, that's the ticket.
  • FreedMike It's not that consumers wouldn't want this tech in theory - I think they would. Honestly, the idea of a car that can take over the truly tedious driving stuff that drives me bonkers - like sitting in traffic - appeals to me. But there's no way I'd put my property and my life in the hands of tech that's clearly not ready for prime time, and neither would the majority of other drivers. If they want this tech to sell, they need to get it right.