Why does the steering wheel shake when braking at high speed?

Many motorists have experienced this problem: The steering wheel starts shaking when brakes are applied at high speed. Often, it's more noticeable when braking on the highway at 60-70 mph. In most cases this issue is caused by warped or unevenly-worn front brake rotors (discs).
Steering wheel shakes while braking Unevenly-worn or warped brake discs (rotors) can cause the steering wheel to shake when brakes are applied.
A brake rotor or disc is the part that is squeezed by brake pads when braking. New brake rotors are uniformed all around and the brake force remains the same when the brakes are applied while moving. An unevenly-worn or warped rotor has thicker and thinner spots, so the brake force changes as the rotor spins. This change in the brake force causes the steering wheel to shake when brakes are applied. You may also feel a pulsation in the brake pedal.

This issue can happen with front and rear brake rotors, but the problem with front rotors is more likely to cause the steering wheel to shake. Some cars have drum brakes on the rear axle. Warped or rusted rear drums can also cause the brake pedal pulsation.

What can cause brake rotors to wear unevenly? This happens for a variety of reasons. Very often it happens when the car is parked outside for a long time without moving. This causes portions of the brake rotors to rust, especially in rainy weather, see the photo. Rusted brake rotors are one of the common reasons for brake pedal pulsation and steering wheel shake.
Rust spot on a brake rotor In this car, the steering wheel vibration and brake pedal pulsation was caused by the rust spots on the brake disc (rotor).
The rotors can also warp as a result of excessive heat, generated while braking. This usually happens in heavy cars, trucks, minivans and SUVs. Other reasons include low-quality material of the brake rotors or pads, sticky brake calipers, seized caliper pins or improper installation. What is the solution?

The solution is to visit your mechanic and have your brakes properly inspected. Mechanics have special tools to measure runout and thickness of your brake rotors (or rear drums). The repair depends on the result of the inspection. In some cases, brake rotors (or rear drums) can be machined (cut).

Most automotive shops have a machine called a brake lathe that can cut a thin layer of a brake rotor or drum material to make it uniformed. Machining two rotors can add $40 to $120 to the brake job.
Your mechanic may recommend replacing the rotors if they are too thin to be machined, or for other reasons. Brake pads and other components may also need to be replaced, depending on the condition.

Is it safe to drive a vehicle if the steering wheel shakes while braking? The only way to get the answer to this question is to have your brakes inspected by a qualified mechanic.

How expensive is it to replace brake pads and rotors? The replacement of the brake pads and rotors can cost from $350 to $750 per axle, depending on the vehicle. It's always recommended to use only high-quality or OEM parts. Keeping your brakes in top shape is an investment in your safety and the safety of your passengers.