Motorcycle Repair: Front Brakes, kawasaki zxr750, dual front

Question
I have a problem with my front brakes which has been getting gradually worse. Vibration when braking from high speed and inconsistent braking at very low speeds i.e. almost an on/off kind of effect. Probably sounds like warped discs I know but I would like to know of any other possible causes. I have no reason to believe that the discs should have become warped. I do know that I need replacement pistons for the calipers but as yet they have not caused the brakes to be binding. I have equipment to check the run-out on the discs but I'm not convinced they are the problem. Just hoping it might be something a bit cheaper. The bike is a 1989 Kawasaki ZXR750 H1 with 30k miles and original brakes as far as I can tell. Thanks for any help you can give.

Answer
Hi Terry.
 You say that you need to replace the pistons on the brakes.  You should do so.  If there is nothing else wrong with the system (air in lines, blockage in lines, etc) then there is no other cause.

Bad pistons will sometimes stick and on a dual front disc bike, if one side sticks and the other doesn't, then you will have a serious adverse yaw problem with the braking which could cause wobbling or vibration while slowing and stopping.

If you know that a part needs replacement, then fix that problem and see if your other problem with the same system goes away.

Remember that your brakes are a safety item.  They are worth whatever you must do to make them right.
What is the value of your life?  My answer to that question is "Whatever it takes to repair a broken safety item".

Good luck.
FALCON