Braking issue. massive vibration is coming from

check you rotors possible slight warp

David, If you feel the vibration in the seat and not the steering wheel, this means the vibration is coming from rear of car, may be a bad rear tire.

sounds like the brake rotors are out of round, check for rust and pitting on the face of the rotors, could be front or rear. If the steering wheel is shaking its most likely in the front, if you are feeling it in the seat rear. These trucks are famous for rear brake issues.

How old are the tires on the vehicle-sounds like a balance problem that happens at certain speeds. Does the vibration happen at any other speeds? When were the tires balanced last? If balance is ok then check out the steering system for loose and worn parts. There is a possibility of a park brake backing plate rust issue- what is the make and model. Newer trucks use a park brake with 4 wheel disc brake that mounts in the smaller cavity of the rotor on the rear axle. This would cause the noise you describe and the vibration.

I believe I would check the rear Brakes. Your truck most likely has rear disc brakes. and most likely has an automatic transmission. Which means you never or rarely use your parking brake. I see it all the time. parking brake which is a drum brake under/inside and part of the rear rotor. It could also be a rear brake issue.Remove the rear tire, and look over the brake rotor and the pads. If everything looks ok there
(rotor is smooth looking on the inner and outer face. they are not rusted and pitted. or gouged) pad has brake materiel of at least 1/8". if that looks ok then remove the caliper and look at the parking brake shoes and hardware. i see a lot of the shoes brake material comes loose from the backing. which will cause noise, vibration, sometimes wheel lock up.

Hope that helps

UNLESS there is a major front end issue the most common cause of the vibration is the rotors being out of round. this is easily correct by having a brake shop resurface the rotors. also the vibration could be coming from the rear as well. the way to determine if it rear or front is the next time you brake somewhere that it usually has the vibration try applying only the parking brake instead of the brake pedal. NOTE....when making this check be sure to hold the parking brake release button to prevent lock up of the brakes. the parking brake only works the rear brakes. this will determine where it is coming from. the back brakes will have either brake drums or either brake rotors. same philosophy but different operating mechanics. either way it can all be corrected by resurfacing the rotors and/or drums

do u feel the vibration in the steering wheel or in the seat,i bet the most vibration was coming out of the front brakes and a little out of the rear brakes,u might want to change the rear brakes if the vibration is still annoying,also were the front wheels torqued to spec when installed?? if not u might end up with warped front brakes again,hope this helped

There's speed sensors at each wheel. You may have got some contamination in front of one of them... sounds like the abs is trying to compensate for un equal speed at each wheel... and something may be blocking a proper read at one of the wheels...

Where do you feel the vibration? if you feel it where you sit it is coming from back which is usually rear brakes. If you feel the vibration in your feet and hands it is coming from the front which could be your ABS or front brakes.