* Warped Rotors: This is the most common culprit. Over time, repeated heating and cooling cycles from braking can warp the brake rotors, causing uneven braking force and the resulting shimmying. The grabbing sensation is a direct result of the rotor's uneven surface.
* Sticking Calipers: A caliper piston that's sticking or a caliper that's not retracting properly will keep the brake pads constantly in contact with the rotor, leading to both grabbing and overheating. This can cause the rotors to warp further, creating a vicious cycle.
* Worn or Damaged Brake Pads: Unevenly worn or damaged brake pads can also lead to uneven braking force and contribute to the shimmying. If one pad is significantly thinner than another, it will create an imbalance.
* Faulty Wheel Bearings: While less likely to directly cause grabbing, worn wheel bearings can introduce play in the wheel assembly, amplifying the shimmying sensation caused by warped rotors or uneven braking. The uneven play would exaggerate any existing brake imbalance.
* Suspension Issues: Problems in the suspension system (worn ball joints, tie rod ends, bushings, etc.) can also contribute to the shimmying, especially when combined with uneven braking forces. The car's instability would make the brake imbalance more noticeable.
What to do:
1. Visual Inspection: Carefully inspect your brake rotors for warping (look for uneven surfaces or discoloration). Examine your brake pads for wear and tear. Check the calipers for signs of sticking or damage.
2. Professional Inspection: It's highly recommended to take your car to a qualified mechanic for a thorough brake inspection. They have the tools and expertise to diagnose the problem accurately and safely. They'll be able to check for rotor warp, caliper operation, pad wear, and suspension components.
3. Possible Repairs: The mechanic might recommend:
* Resurfacing or Replacing Rotors: If the rotors are warped, they can be resurfaced (machined to a smooth, even surface) if the warp isn't too severe. Otherwise, they'll need replacement.
* Replacing Brake Pads: Worn or damaged brake pads should be replaced.
* Caliper Repair or Replacement: Sticking calipers may need repair or replacement.
* Wheel Bearing Replacement: If wheel bearings are found to be worn, they'll require replacement.
* Suspension Component Replacement: If suspension components are contributing to the shimmy, they will also need to be addressed.
Ignoring this issue is dangerous. Uneven braking can lead to loss of control, especially at higher speeds. Get it checked out immediately.
