Most of the time it is caused by the disk (rotor) being warped for previous "locking up" the brakes. If you've ever slammed on the brakes that could be the reason why. Basically it's a rotor problem most of the time.
If it only happens when you are braking I would suspect warped brake rotors. Other reasons the front end could shake would include unbalanced tires or the vehicle needing realignment. Whatever the case may be; driving a car in this condition is unsafe and you should repair it or have it repaired before you drive it again.
You have a warped rotor. Brake pads need replacing and the rotors turned or replaced.
realignment, 60 to 80 bucks
I don't know you tell me.
A front tire can lock up while driving due to factors such as sudden braking, worn brake pads, a malfunctioning anti-lock braking system (ABS), or low tire pressure.
Check for warped front rotors. under slight brake application it may not shake. But under hard braking such as getting off an offramp the truck will shake and the brake pedal may pulsate slightly. Chances are real good this is your problem.
It might be a broken motor mount or transmission mount.
Braking. Driving on ice.
Could be a vacuum leak
Loose motor mounts.
bent wheels or a broken cord in a tire or a deformity in a tire.
Wheel bearings and allignment. Can be tires as well and sometimes even a bad motor mount.