When you press the brake pedal, and brake piston pushes the pads into the rotor. But, there is no spring that makes the pads pull away from the rotor. So, what makes them pull off the rotor? I assume they don’t just stay pressed against the rotor and keep scraping…

With disk brakes, there is no mechanism to “recoil” them. With brake pedal pressure removed, the pads intentionally just ride there and “self clean”. The resulting friction is negligible.

The answer is a square cut seal, that helps pull the pads back just a hair but its not visible to the naked eye.

WheresRick: I had forgotten about the square cut seal. I guess I was thinking the OP wanted an answer similar to how springs in drum brakes retract the shoes. I stand corrected. But to be clear, that square cut seal acts as an “assist” because it simply wants to go from a tilt position (when fl…

Were both right, both statements are true,

Yes to all above, plus, rotors always have some wobble due to lack of pre-loading the bearings and the wobbling throws the pads out, overcoming the compression from the caliper slides and/or piston friction.

The square cut seal may explain the piston, but it doesn’t explain the pad on the other side. With the brake pedal depressed, hydraulic pressure holds the brake pads tightly to the rotor. It takes a lot of pressure to hold them there, that is why disc brakes have power assist. Foot off the pedal …

Keith, My race car has no power assist and has plenty of pressure. The key to this is the ratio of the master cylinder to the slave (brake end) cylinder.

The seals and dust boots tend to retract the caliper piston slightly, but the slight amount of play in the wheel bearings allow the rotors to wobble enough to push the pads back enough so there is virtually no friction…

CapriRacer, how much does your race car weigh? That has a lot of bearing too. Even my 68 Datsun SSS had power assist for the disc brakes as did my wife’s Chevy Sprint (later Geo Metro).

I have “manual” discs I put on a 71 Chevelle with around 575 HP. It stops just fine without a booster. Its not for some frail old lady though. :wink: Also some vintage 60s vettes but they would be in the “lighter” category. The Chevelle has all the original metal…

How do brake pads "recoil" after you let go of the brake pedal?

Maintenance/Repairs

keith September 16, 2013, 9:07pm 16

A little clarification here, the cross section of the O-ring is a square, not the shape of the O-ring.

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How do brake pads "recoil" after you let go of the brake pedal?

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