Intermittently, my brake pedal will drop slightly, and there will be a loud clunking noise, metal on metal sounding. Normally happens at slow speeds, weather conditions don't seem to be a factor.

  • That does seem way odd. Is the metal to metal clunk inside the passenger compartment or outside? Two minute test. Turn the car off, vehicle in Park, key out of the ignition, flashlight in hand. Open the drivers door, carefully kneel on the ground outside of the car and look underneath the steering wheel area. Push the brake lever with your hand. Do you see anything not connected? Do you hear the metal on metal clunk when you do this? If outside, it's possible there are loose bolts at one of the wheel cylinders. If so, that is dangerous and needs to be fixed pronto.
    – zipzit
    Commented Apr 26, 2016 at 21:57

1 Answer 1


sounds like something to do with the brake hydraulics. possibly brake booster?
Need to state more information like HOW & WHEN things happen... What CAR? etc.
The noise is very odd, but MIGHT be attributable to sticking brake components that suddenly come loose. Possible that some other kind of electronic control on your brakes is acting up as well, whether in reaction to sticking calipers or not. (Traction Control, Electronic Stability, etc.). Not sure if your car has these slightly more techy features.
Unless you work on cars, take it to a mechanic and get it diagnosed and fixed.
Brakes are safety critical so you dont want to leave it alone or do shoddy work.
If you want, u can get it diagnosed and come back here to help you not get swindled.

How hard are you braking when you experience this?
Do you know what the feeling of ABS turning on feels like? The pedal moves a little back and forth and you will feel the movement when braking, sound similar?
I am pretty sure there is some procedure to test the ABS. If anything, you most likely can at least do a resistance check on the electronic components, which takes like 10 minutes and no $$$ at all. Have someone do some sort of REAL diagnostics before simply replacing parts.

  • it's a 2004 Pontiac Grand Prix. It usually happens when slowing down or braking into a turn. I took it to a mechanic, they looked at all the brake parts and couldn't see anything. They drove it repeatedly and of course it wouldn't do it for them. Hubby is a gear head, thinks it may be a sticking caliper? Mechanic says it might be the ABS module (BIG bucks) he's pretty trustworthy, but stumped and suggested I get other opinions before we go the route of replacing that part. I'll mention the brake booster and see what they both think.
    – Lisa
    Commented Apr 26, 2016 at 21:52
  • (edit/include that in your question) i also think it could be a sticking caliper, but ABS is a good thing to check. (if you mentioned the pedal moving, i think thats probably why the mechanic thinks its abs). Commented Apr 26, 2016 at 22:31
  • Car has traction control and stability features, fully loaded for a 2004 model. Has ABS also.
    – Lisa
    Commented Apr 27, 2016 at 1:22
  • Braking pressure is normal for slowing down/stop light, braking into a turn. It's never happened during hard braking or at high speed braking. Hubby and mechanic are stumped and we all want other opinions before we start replacing parts. Thanks agent provocateur for your advice. I'll ask about resistance check. The pedal moves down quite a bit when this happens, almost as if there is a problem with the brake lines (pumping brakes to get them back up) The pedal moving more extreme than the ABS coming on and off. car also has Traction Control an tried with on / off too, makes no difference.
    – Lisa
    Commented Apr 27, 2016 at 1:28
  • Got it figured out, it was the front wheel bearings and the ABS sensor. Total repair cost $224.48.
    – Lisa
    Commented May 5, 2016 at 20:17

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