Annoying Brake Pedal Pulsation on my 2020 C300

ClearTheCode admin answer:

Brake pedal pulsation, particularly noticeable at higher speeds, is a common complaint and usually points to an issue with the brake rotors or related components. While 'warped rotors' is a common term, it's often more accurately described as uneven rotor thickness or runout.

Here are the most likely causes:

1. Uneven Rotor Thickness (DTV - Disc Thickness Variation): This is the most common cause. It's not typically a 'warp' but rather an uneven wear pattern on the rotor surface, often caused by:
   • Improper break-in procedure after new pads/rotors.
   • Overheating the brakes.
   • Improper torqueing of wheel lug nuts, leading to rotor distortion.
   • Sticky caliper pistons causing uneven pad pressure.
2. Rotor Runout: This refers to the rotor not spinning perfectly flat relative to the hub. Even a slight runout can cause pulsation. This can be due to:
   • Contamination or rust between the rotor and the hub.
   • A bent hub flange.
3. Sticky Caliper: If a brake caliper piston or slide pin is sticking, it can cause the brake pad to drag unevenly on the rotor, leading to localized overheating and DTV.
4. Suspension/Steering Components: Less common for pedal pulsation, but worn ball joints, tie rods, or wheel bearings can sometimes exacerbate brake vibrations.

When to see a shop:

You should have your C300 inspected by a professional mechanic. While the car is still braking, the pulsation indicates a problem that can worsen and potentially affect braking efficiency and safety. A shop can measure rotor runout and thickness variation, inspect calipers for proper function, and check for any underlying suspension issues. They will likely recommend resurfacing the rotors (if within minimum thickness specifications) or replacing them, along with new pads, to ensure even braking.