Car shakes when I press brakes

I have taken my car to mechanics because my car shakes when i step on the brakes.Can you tell me why that happens please?

I had my tires balanced but this did not help.

I bet your rotors are warped, probably due to overtorquing the wheel nuts.

The mechanic did say they were rusty.Do i put brand new ones in or rebuilt rotors?

Yep-- probably a warped disc rotor. Usually the cause is from overheating the brakes, especially if they get wet when they’re really hot. I’ve never heard the overtorqued nuts cause, but I suppose it is possible. Cheaper rotors are also much more prone to warping.

They may be able to put the rotors on a brake lathe and shave off the high points, but depending on the make and model it’s often a cheaper just to replace them.

All brake rotors get rusty. That is completely normal so ignore? that comment from the mechanic.
The rotors are more than likely warped but depending on the vehicle’s mileage a loose wheel bearing or suspension component can also cause a brake shudder.

If the brake shudder is pretty severe, and depending on the type of vehicle, chances are you would need new rotors IF the shudder is rotor related. Rotors can be machined but in severe shudder cases this usually means they would have to be turned down thinner than what is acceptable. This is a safety issue so they are better off being replaced.