it only shakes when brake pedal is deppressed.can an allignment fix this?i just changed the brakes the rotors are fine.

 

warped rotors can cause that problem. did it do it before the brakes were changed and the rotors were "fine". my F150 did that and i found the cause to be loose bushing in the idler arm that attaches the steering links to the main frame. jacked the front end up off the ground and set the A frames on jacks. have buddy jerk one tire back and forth and looke under the truck. if one tires is moving an inch and th eother is not moving side to side, look for the location of the slop. either tie rod ends or idler arm.

 

I had a front end shimmy when braking a while back and the front wheel bearings needed to be tightened up a little bit. Worked for me!!

 

have you rotated your tires lately, that will cause that?

 

What do you mean by the "front rotors are fine"? Did you check them for run out?

If you're only feeling the vibration during brake application, 99% of the time it's due to warped rotors. Get them resurfaced.. or replaced (if they are too thin).

 

I second the wheel bearings! Also, new rotors. I thought mine were fine, but the shop recommended I replace them. It made a world of difference.