* Warped Brake Rotors: This is the most likely cause. When you brake at higher speeds, the heat generated can warp the front brake rotors. This warping causes the brake pads to grab unevenly, resulting in the pulsating feeling in the brake pedal and steering wheel. Visual inspection might not always reveal warping; a mechanic needs to check for runout (unevenness) on a lathe.
* Worn or Damaged Brake Components: Severely worn brake pads, calipers sticking, or damaged brake hoses can contribute to uneven braking and vibrations. Inspect the brake pads for thickness and even wear. Listen for any unusual noises from the brakes, which could indicate sticking calipers.
* Ball Joints or Tie Rod Ends: Worn ball joints or tie rod ends can introduce play in the steering system. At higher speeds, this play can amplify and cause vibrations that worsen under braking. A mechanic can check these components for play and wear.
* Wheel Bearing Issues: A bad wheel bearing can create vibrations that are felt through the steering wheel and brake pedal. The vibrations might increase with speed and braking. Listen for any humming or growling noises while driving.
* Tire Issues: Although less likely given you checked the lug nuts, an issue with the tires themselves – like an imbalance, a bulge, or uneven wear – could contribute to vibrations. Inspect your tires carefully for any damage.
What to do:
1. Have a mechanic inspect your brakes: This should be your first step. They can diagnose the specific problem with the brake rotors, pads, calipers, etc. They'll have the tools to properly measure rotor runout and assess the condition of other brake components.
2. Get a front-end alignment check: If the brake issue is resolved but shaking remains, an alignment check can pinpoint problems with the suspension.
3. Inspect tires and wheels: Though you've already checked the lug nuts, thoroughly inspect your tires for wear, bulges, or embedded objects, and check the wheel balance and alignment.
Ignoring the issue could lead to more serious problems, potentially compromising your safety. It's best to get a professional diagnosis and repair as soon as possible.
