2005 Mitsubishi Lancer brake pedal shakes

There's a number of things to watch out for when installing a new rotor and other brake parts. Who replaced the half shaft and did the brake work?

Take it back and explain the problem. There can be some debris or rust that got caught between the rotor and hub or between the rotor and wheel. That will prevent those parts from sitting squarely against each other. Also, he should know to always use a torque wrench on the lug nuts. Power tools will over-tighten them and possibly cause the rotors to warp after they get hot from normal braking and you hit a puddle of water. The warping is due to the uneven clamping forces on it.

New rotors can be warped too. Any job involving brake or suspension parts gets a test drive and he should have noticed the vibration and diagnosed the cause. If that vibration wasn't there until a few weeks after the work was done, it is likely the new rotors were made in China. There's nothing wrong with the quality of the parts, but when we make parts out of cast iron, we let them sit and "age" for 90 days before they get the final machining. The Chinese cast 'em, pack 'em, and ship 'em, then they age on your car. Warping is very common. A light machining will take care of that. Some people demand new rotors, but those will just do the same thing in a few weeks.

I don't have a clear idea of the time between when these things occurred. I just listed some of the common things we run into. To narrow it down we need to know when you noticed various problems or if they started occurring right after some work was done. Your mechanic will ask similar questions so he can find the diagnosis faster and cost you less money if it comes to that.