When I apply the brakes the front end shakes ?

you need to check the rotors install new one if you have not done that yet. Here is a guide that can help

https://www.2carpros.com/articles/steering-wheel-shakes-when-accelerating-or-braking

and

https://www.2carpros.com/articles/how-to-fix-a-car-with-shaky-steering-wheel-when-braking

Please go over these guides and report back.

Brake pulsation comes from rotor thickness variation. Thickness variation comes from a rotor that has run-out. Run-out comes from incorrect or uneven wheel nut torque, dirt/rust between the rotor/hub interface or a hub that has run-out. You first need to fix the cause of the run-out to prevent the repeat problem of brake pulsation. All GM dealers have a very specific TSB that address this issue and when the belletin is followed and the run-out measured and compensated for, the problem is fixed.

BMRFIXIT is right replace the rotors, but also, clean the hub up good. Remove all rust if possible. This will help alot.