u/centstwo

Vehicle: 2012 Kia K5 / Optima

Brake Setup: Front / Rear Single-Piston Floating Calipers (OEM Mobis Components)

Hey everyone,

Had a terrifying experience today and luckily I was going slow. Looking for a definitive diagnosis from the pros on what went wrong and what my best options are for repair.

The Story:

I was braking for a speed bump today when the brake pedal suddenly lost all resistance and went straight to the floor (zero braking power). I managed to stop safely using the emergency brake. When I got out, I found a massive puddle of brake fluid and this piece (in the photos) sitting on the asphalt right where it happened.

Important Background (The Plot Thickens):

Just one week ago, I had a mechanic replace the brake pads with brand-new OEM Mobis pads.

The reason I changed them was because I was hearing a terrible metal-on-metal grinding noise BEFORE the replacement.

After the new pads were installed last week, the noise completely vanished and the car braked fine—until the pedal went dead today.

The Part (Look at the photos):

It’s obviously a caliper piston, but take a close look at the top/front lip of it. It is severely chewed up, ground down, and chewed to pieces.

My Theory (Let me know if I’m onto something):

Since there was no grinding noise after the new pads were installed, this heavy damage to the piston lip must have happened before the pad change (when the old pads completely wore away to nothing and the piston itself started grinding against the rotor).

It seems the mechanic who did my pads last week saw this mangled piston, ignored it, and forcefully compressed/shoved it back into the caliper bore to slap the new pads on. This likely tore the internal seals. Today, when I stepped on the brakes at the speed bump, the hydraulic pressure blew the compromised piston completely out of its bore.

My Questions for the Experts:

Does this diagnosis make sense? Or is there another mechanical explanation for how a caliper piston completely ejects itself just a week after getting brand-new pads on a 2012 Kia Optima?

What are my repair options? Given that the piston is physically chewed up and the internal caliper bore/boot seating area is likely compromised, is a rebuild kit even on the table, or should I just buy a completely new complete caliper assembly?

Collateral Damage: Will I need a new rotor (disc)? Also, the new pads are only a week old, but they got absolutely drenched in brake fluid when the piston blew—are they ruined, or can they be saved with brake cleaner?

Thanks in advance for the help. Stay safe out there!

A blonde has spent her whole life fighting the blondes are dumb stereotype. She graduated near the top of her high school class. She went to business school. She became a personnel manager at a hospital. Soon she was promoted to regional manager. She was on her way to a healthcare convention. The flight landed and she rented a car to get to the convention center.

She is driving through the countryside. As she's driving past a cornfield, that was recently harvested, something catches her eye - another blonde in a rowboat, rowing furiously in the middle of the field. She stops her car, gets out, and shouts, "Hey! You, out there in the boat"

The blonde in the rowboat stops rowing and looks at her. "Yeah, you!" the blonde motorist continues. "It's because of you that everyone thinks blondes are stupid! And if I knew how to swim, I'd swim out there and kick your ass!"

How the hell do I get this panel off

r/AskInternetRandos

Brake pedal went to the floor, brake fluid dumped, and this Piston fell out on the road! Post-pad-slap disaster?

Blonde Fighting The Stereotype