It's an 86 5000S. After driving for several minutes, I step on the brake, the car shakes. Test drive for 10 mins. The right front brake is hotter than the other three(the rear ones are cooler than the front ones in gerneral, I think). There is also more brake dust on the right front wheel. Here are my questions,

1. I have a warped rotor. Am I right?
2. How can I tell the rotor is warped or not? Eye spot or some better ways?
3. Two front rotors must be changed together?
4. Any suggestion on where to buy rotors and what kind?

 

Check the caliper bolts and make sure that they are not worn. If the caliper is not releasing fully then the rotor will overheat and eventually warp.

you should always change you rotors in pairs.
In my experience when you are doing brakes you should replace everything. A single faulty component can cause others to fail early causing you to redo the job sooner than expected.

Change the following.
rotors
pads
Caliper bolts
Any hardware, boots etc.

good luck

Sam.

 

I'd look into replacing that as well

 

You may have more than just one problem.
Warped rotors mean that when you press the pedal, you'll feel the vibration from the warping of the rotor both in the footpedal and the steering wheel, and the car will shake. But unless it's very severe (maybe it is) where the whole car shake significantly, you still have effective braking action. So you know you have at least one warped rotor
measuring rotors requires a Micrometer. The machine shop that will grind down the rotor to make it smooth again will measure it for you. If the rotor has already beenground, or worn significantly, it may be too thin to be reground and in it goes to the trash. Grinding or cutting the rotor is cheap, maybe 10 or $15 each, and that is obviously much much less expensive than purchasing new. They will tell you what aftermarket parts are available, as opposed to the cost of new Audi rotors
temperature differential: I think you have correctly noticed that the left front brake is not working at hard as the right front, so there is obviously defect in the left front. It could be that the caliper, which is less likely, or perhaps the caliper bolts are stuck not allowing the caliper slide back and forth and therefore decreasing braking effort . So you probably can count on new pads , rotors on both front (or at least re-cut rotors), but you also have a problem with the left side caliper that needs to be evaluated.
Master cylinder: from what you written down, I don't seen a problem with the Master cylinder.

 

Rob, I wish I can afford the "Brembo".

 

thank you. I was thinking the right side brake is bad.

 

what a maitenance nightmare that car was.