by the way thanks for all the replies

 

I went to the mechanic and him check out my rotors, they arent warped and there isnt anything wrong with them , I had my rotors and brakes changed about a year ago, anybody have any ideas? my mechanic was suggestion shortening the rotors, he says that might help

 

How about lug bolt torque? Are the bolts gunned on, done with a breaker bar, or actually torqued? Having them unevenly tightened or blasted on too tightly will distort them and create a pulsation. Most shops gun them on. Loosen them and use a torque wrench to torque them to 90 ft-lbs in the proper skip-one pattern and see if this helps over a day or so.

 

Well, you can certainly try a torque wrench, but most people don't use a torque wrench and few people have problems.

If it only happens when braking them it's still most likely a brake problem. Note that rotors do not always "warp" when people say they do - a lot of the time it's your brake pads leaving deposits on the rotors.

 

Most owners use a wrench but most shops gun them on. He was at a shop so they probably gunned them back on and from what I've seen they put them on with way too much torque. Retorque them properly. And yes, pads can leave deposits as well and cleaning the rotors is a good idea but check the torque on the bolts. It's probably 30-50 lbs too high.

 

I thought the torque spec was 80 ft/lbs...?

On that note, what are the long term effects of over torquing lugs? The shop I got my tires from torqued them beyond anything reasonable when I last had them rotated/balanced (free cuz I purchased the tires there)- this was before I painted them, and when I went to take them off to paint them, I had to put one foot and as much body weight as my balance would allow on the other end of the breaker bar and simultaneously pull up really hard to get them to break. After I put them back on and used a torque wrench to put them at 80 ft/lbs, I tried breaking them again and they broke with significantly less effort so I'd have to guess they were over by at least 30 ft/lbs.

Also, OP: (to make this post not a complete threadjack) it is also possible that the wheels were put on crooked. Hubcentric wheels can be testy I've noticed. If you don't carefully finger-tighten the lugs in the star pattern making sure that its fully seated straight before torquing, you could have 2 or 3 lugs tighter than the others and this can cause a bad wobble and even your lugs to start coming loose. Unfortunately, I have experienced this and it scared about 7 shades of **** out of me.

 

I carry a long pipe in the trunk to put over the wheel wrench as the nuts are often too tight to undo without leverage assistance. This happens even after I have torqued them (months after). Must be corrosion between disimilar materials (steel/aluminum). The wheels also get stuck on the hubs for the same reason so I have taken to smearing all contact surfaces with anti-seize during assembly.

 

If runout of the rotors really is ok (limit is about 0.002" - 0.003" I think), then variable friction coefficient of the rotor surface due to uneven bedding in of the pads, or uneven heating, can cause this. The mating face with the wheel hub must be very clean when assembling the rotor - this can cause runout. Also, check suspension joints for wear as looseness will exagerate any vibration.

 

Couldnt it just be the alignment?

 

Not impossible, but alignment issues shouldn't show themselves only while braking. Of course, the loading of a car definitely does change when you hit the brakes, so it is still possible.