first off, disks almost never warp, though shops love to tell you that - i will first address the issue if it is indeed brakes:
what almost always is the case, is uneven deposits on the rotors - there is actually a website that explains this in great detail, but i can't find the link right now - it also has a great break in procedure
unfortunately, the result and remedy is almost always the same as if the rotors were warped - you end up having to replace pads and rotors
you can try having the rotors skipped, but it may not work - once uneven deposits are laid down, the rotors start heating and cooling oddly, and create "hot spots" - these can be seen in the form of "blue streaks" or "blue spots" - they result in the pads not going over them smoothly, and they speed up and slow down unevely, which feels like juddering - in reality, they are grabbing and letting go grabbing and letting go so quickly that we can't tell the difference
the pads will be toast in either case
now, it may not be brakes - there are a couple of things that could cause this - to determine if it is one of them, i need to be sure that it does not do any juddering or pulsing below 70, regardless of the force applied to the brakes - brakes should be able to be felt, though to a diminishing degree, regardless of speed
if it indeed is only at 70, it could easily be a balance issue - believe it or not, this happens a lot - most shops only spin balance - this is frequently not good enough, and road force balancing is needed - this should be done at least every 10k miles on a car like this
it could also be a bad wear pattern in the tire - carefully inspect the tire - run your hand across the surface of the tire front to rear and then rear to front - if you feel any "stair-stepping" you have likely found your problem - if it is on the inside, you need an alignment at minimum - if it is on the outside, or across the entire tread pattern, unfortunately it almost always means struts - this is the symptom that shows up long before you would feel worn struts in suspension travel
a worn suspension component can cause this - castor blocks are a prime candidate - as the load is shifted to slow the car down, the component moves, making for a change in toe that fluctuates - it often shows up as a high speed judder under braking
lastly, a loose wheel bearing will cause this too - check that out
hope that helps
