A cost effective brake upgrade is to replace the single piston calipers with the two piston calipers that are found on many different Audi models, such as the D2 A8, C5 A6 with 2.7T engine and B5 S4. The B6 A4 upright has the same caliper bolt spacing as the B5 S4, so the caliper bolts right up. Not only is there a second piston to increase stopping power, the caliper utilizes a 320mm diameter rotor, which is a good amount larger than the stock 288mm 1.8T rotor. The larger rotor helps absorb more heat under braking to resist brake fade as well as increasing braking torque. So, let's get started!
Rebuilding the caliper (optional)
I had already rebuilt these calipers, but they are very easy to disassemble. They break down into the three main sections. The left section is aluminum and houses the two pistons. The second piece is what holds the slide pins and the anti rattle spring (removed in this picture). The last piece holds two of the brake pads and essentially holds everything together.
Here you can see the two slide pins, they get bolted to the middle piece shown earlier and they slip into the rubber bushings on the piston housing.
The triple square bolts thread into the last piece.
So, if you picked up a set of these used from a salvage yard, I would highly recommend rebuilding them. As you can see, it's fairly easy to disassemble the calipers and replace the piston seals.
Replacement
Stock brakes
Unclip the brake pad wear sensor. The connector that goes to the brake pads will just twist a quarter turn and can be pulled out of the bracket.
Next, slip the rubber grommet for the ABS/wear sensor out of the bracket. If it is difficult to pull out, I find that a shot of silicone spray helps.
Take two wrenches and undo the connection for the hard brake line from the caliper to flexible line.
Since we are going to remove the caliper, rotor and pads together, all you need to do is remove the two fasteners holding the brake carrier to the spindle. There is one on top like shown above and then one underneath. Then you can remove the whole assembly.
Take the 320mm rotor and place it on the hub. I find that a spare lug bolt with a large nut slipped over the threads helps to hold the rotor in place while you get the caliper on.
Bolt the caliper down using the two fasteners you removed earlier.
Reattach the hard line. Make sure that it doesn't get cross threaded.
Install the brake pads, they just slip in. Reattach the brake pad wear sensor if your pads came with one.
Now all that's left is to bleed the brakes! The two person method will work here, but a Motive Power Bleeder makes it so much easier and a one man job.
