My 91 F-150 4x4 has a big shaking action when braking. The right rotor was replaced, and the drivers side was said to not need turning, a few months ago.
I went and had an alignment Saturday.
Steill shakes the whole truck above 30 mph or so. The brake pedal pulsates when stopping at lower speeds.

Any thoughts on what this might be?

Thanks

 

Replace the other rotor, once you cut the rotor it is more susceptable to warping.

 

It may be your rear brakes, Try driving at 30mph and slowly apply em.brake to see if you get the pulsation from the rear brakes. But be carefull.

 

THis might sound a little dumb but try checking wheel balance...

 

Had the wheels balanced about a month ago.
Gonna go ahead and see if I can get a free estimate from a brake place......
get them to tell me the problem......and get it fixed for less, if not myself.
Figure maybe thats about the best way to go.

 

That is a great idea!!! Please post what you find out.

 

if you machine a brake rotor, it is not more prone to warping, as long as you dont exceed the minimum thickness. brake pedal pulsation is NOT CAUSED BY WARPED ROTORS. it is caused by thickness variation in the rotor.if there is not a uniform thickness in the rotor, it will push out on the brake pads every revolution when it hits the "high spot", transfering the pulse through the hydralic line to the master cylinder and the brake pedal.thickness variation is caused by rotor runout.it takes tens of thousands of miles to make thickness variation from a rotor that has excessive rotor runout.