99 taurus shakes when braking

My car has a bad shake when braking. This only happens when the brakes heat up. It does not happen when first start and drive the car, you have to drive a little before it starts, then it just gets worse. Some days its not bad at all. Now I have replaced the pads twice, rotors 3 times(warranty), new calipers, new lines. Still have the vibration. I believe that I have eliminated the brake system for this problem. The car drive perfect, no pull, vibrations, tire pull, tire nothing, car nothing untill you touch the brake. When you hit the brake, the entire car shakes, you feel it in the steering wheel, seat of your pants, etc. Now if you stop the car using the E-Brake, none of this happens. So its in the front end. I want to think bearings, but they don't make any noise, and seem fine. Car has 70k. Don't want to throw more money at it and find vibration when done!!
Any ideas?????
Help Please....

Now I have replaced the pads twice, rotors 3 times(warranty), new calipers, new lines. Take the tires of and calipers loose and see if there is any wobble to the rotors, only takes a tiny bit to make it shake. At 70K miles I doubt there's any severe front end wear that would require replacing parts. Problem easily cured and I'd consult with the Ford place and shops that do brake & muffler work. Might just run into a tech who knows exactly what the problem is. Run a search here and on the Mercury Sable forum.

have used a run out gauge on the rotors and the spindles and every thing was within 5 thousands. Like I stated before, only happens when something "heats" up, does not happen all the time. I did clean the hub before putting rotors on. Could 4 sets of rotors be heating up, warping that bad and cooling off back to shape to where a runout gauge dont show it? And 4 sets all doing the same thing? I really find that hard to believe. Can someone tell me different?

I know it may sound weird, but do you have ABS? Is it possible the ABS is being activated when you brake after the brake system heats up? The rapid pulse by ABS can feel like vibration. If it is going bad and is being activated on light braking? ?? Just throwing out a wild a$$ guess.

If you have a buddy at a transmission shop, you may want to see if they can put their scan tool on it and watch the torque converter clutch (TCC) to make sure it is unlocking when braking and that the input and output shaft speed sensors indicate that it's unlocking, rather than just relying on the PCM input to unlock the TCC.

-Rod

Let me add.. No ABS, I am 1st and only owner, never been wrecked. On the tranny thing, I see what you mean, but when I've worked on cars with stuck converters before, they jerk like they still want to GO.. Wouldn't this condition still exist even if you stop with the emergency brake?
Remember, I have no problems if I stop with only the E-Brake. The car stops smooth!! This can get to be a severe shake if you drive a while, sorta like the wheels are falling off. (I know they are not). Imagine going over constant baby speed bumps till you let off the brakes, and slows as the car slows. It starts small and gets bad.
??????

Maybe you need to check the subframe mounts and the unit body structure for cracks. My first car, and '88 Escort EXP, had a broken unibody seam. Everytime I would apply the brakes, the car would dive and pull violently to one side. Like you, using only the parking brake would not exhibit the dive or pull. I was all over the front braking system, replacing hoses, rotors, moving tires around, etc. Then had it on the hoist changing the oil and caught a slight reflection off of some polished metal. Welded the seam up and the pull and dive was gone.

Will check bushing and things like you suggest.

Well hope this post helps others. I hope I have finally solved my problem. I still can't believe it, but after checking all the front end parts over and everything is good and tight, my problem seems to be with the stupid rotors. As I stated before, I've been through "4" pairs. 3 BRAND NEW PAIRS!! The first was on the car when this all started. The shake never improved, or got worse with changing the rotors, thats why I ruled them out. Today I gave in and Turned them, and YES, the brand new rotors where out!! So far, So GOOD!! So I will be a firm one from now on, If you have a Shake or vibration, no matter what, Turn the rotors FIRST, New ones Can BE WARPED (3 Sets in A Row)!! I know thats wrong, but ?????
Hope it stays fixed..
Thanks all!!

Yesterday on automotive talk radio show I hear your same problem and the host immediately said it was the rotors. Like yours, they had just been replaced. Host said it only takes 1/1000 th of an inch to make the car and pedal shake and when he does a brake job and that happens first thing he does is have the rotors turned and 90% of the time solves the problem.

He gave Bramnd name of a rotor that is usually true but I don't recall it. OK, glasd you got it fixed and happy motoring.

While brand may certainly have an effect on the true-ness of the rotors, the way they are stored at the parts house will also have an effect. Typically the boxes will have a marking such as "Store flat" or "This side up." Those are not just recommendations, but the way that the manufacturer wants the rotors stocked to prevent, or limit, the warping while sitting on the shelf with other heavy rotors stacked on top of them.

When I was working at Dad's shop, we got to the point where we were running new rotors across the brake lathe before installing them to avoid comebacks. We'd set up to take 0.001 inch off each side. Sometimes we'd have to cut 0.003 off. Anything more than that and they were returned to the supplier.

-Rod