1999 a4 quatro 1.8t

the rear pads were completely gone and the brake caliper cylinder was completely extended. I tried to compress both of the reae wheel cylinders but neither will budge. Is there a secret switch or bolt that needs to be removed? is it due to the emergency brake set-up? I even tried to open the bleeder valve but it still wouldn't compress

 

The rear pistons, unlike the front pistons, require that you turn them while pushing them in. Some people do it manually using various methods, or it's possible to order tools like this that will do it: http://www.ecstuning.com/Audi-B5_A4-..._Tools/ES9747/

 

You can go to AutoZone or any other big box parts store and "rent" the tools you need to twist and compress the piston for free. You have to "buy" it, then return it. That kit in the link is exactly what you're looking for... Pretty easy to use, and you should be good, as long as you didn't blow any seals in the process of fully extending the pistons. If that's the case, and rebuild kit sould do the trick, and they're fairly cheap.

Almost forgot... make sure you open the brake fluid resevoir before you compress the pistons, or you run the risk of killing your master cylinder. Do not top off the brake fluid (it should look a little low) before you compress, or else you will have brake fluid spilling back out.

If you decide to change the front pads as well, after you put everything back together, if the brake fluid looks a little low, then you can add some... DOT 4, fyi...