Here is the basic procedure for changing A4 brake pads. It assumes that you have an average amount of tools and basic, but not mechanic-level knowledge. It was developed for a 98 2.8 A4Q, but should apply to others.

Front Brakes:
Tools: 7mm Hex Key, Needle-nose or similar pliers. 17mm socket and wrench for lug nuts. Torque wrench recommended. Possible need for C-Clamp or large pair of pliers (for pushing piston back on front calipers).

Put car in gear and engage emergency brake.

Remove plastic caps over lug nuts using Audi's U-shaped plastic tool (see tool kit or glove box).

Loosen lug nuts.

Jack up front wheel (see jacking points in owner's manual). I used a small floor jack instead of Audi's jack.

Remove lug nuts and remove wheel. (Recommend using jack stand under car somewhere, but you don't have to get under the car).

On the back side of the caliper, near top and bottom, you will find 2 black plastic plugs, about 1/2" diameter. Pull these out by hand. Behind these plugs are the hex bolts.

There is a wire "spring" on the outside of the caliper. Pull it off with pliers. It has a few pounds of tension behind it, but isn't that bad to remove or re-install (can actually be done by hand).

Remove the two hex bolts with the 7mm hex key or equivalent. (I think 7mm was the size). Mine weren't on all that tight and they were easy to get out.

Now the main part of the caliper is loose. Pull it straight back. It will still be attached by the brake hoses (and ABS wire?). Lay the assembly down on top of the nearest suspension member, so it isn't hanging by the hoses.

Remove the back pad. It just pulls out. It has a neat 3-prong clip that holds it to the inside of the caliper piston. Remove the front pad. On mine, it was essentially glued to the caliper, so some force, or a screwdriver might be required. I think the "glue" was applied by Audi to absorb vibration and reduce squealing.

Take note if there are any arrows, etc. on your new pads indicating which side is up (same as which way the tire rotates going forward). The original Audi front pads have these. My Ferodos and the Audi rear pads didn't.

Install 2 new pads in the same way as the old ones came out. You'll have to decide what to do about the "glue" situation. There was enough left on my calipers that the new pads stuck to it pretty well. Or, there are commercial rubberized coatings (liquid or spray) that you can apply to the backs of the pads to reduce the tendency to squeal. I used one of these when I reinstalled the original pads.

Try to fit the caliper back into position over the rotor. If the pads you are replacing have nearly all of their original thickness remaining, it might fit. If not, you will need to push the piston back into the caliper enough to make it fit. I didn't have to do this (in front). It is probably too hard to do by hand. In the past (other cars), I have used a C-clamp fit over the piston and the back of the caliper to push it back. (Protect the piston face with a scrap piece of wood). Or, a large pair of pliers would work similarly. Note that as you push the piston back, the level of fluid in your master cylinder reservoir will rise. You might have to remove some. (A clean turkey baster works well as a siphon for this).

Reinsert the 2 hex bolts and tighten. (Try to get it about like it was, somewhere between falling apart by itself and breaking something. I don't have the torque spec.) Reinstall rubber plugs.

Reinsert the spring on the front with pliers.

Clean up/wash/wax wheel, front and back, if you have the time or inclination.

Put wheel back on, snugging up lug nuts (not final tightening) while wheel is still in air.

Lower car. Use torque wrench to tighten lug nuts. 80 foot-pounds is the Audi spec for my 2.8 wheels. Push plastic lug nut covers back onto nuts.

Repeat with other side.

Note: Your new front pads might come with a wire and connector hanging from them. This is a wear sensor used on some models, but not the A4. Just cut it off close to the pad.

Rear Brake:

Emergency Brake must be OFF. Otherwise the pads are clamped to the calipers and you'll wonder why they won't come loose. So, chock front and back side of at least one other tire to prevent vehicle from rolling.

Tools: 13mm wrench. Another wrench, possibly 13mm, but I used an adjustable wrench for this. It needs to be slightly thinner than the typical wrench.

Jack up corner, remove wheel as above.

The mechanism in back is different, so the procedure is different. There are two bolts on the back of the caliper. However, if you try to loosen them, they will turn but won't come out. This is because there is a nut near the bolt you are trying to remove and they are locked together. You need to put another wrench on the nut to hold it in position while you loosen the bolt. There isn't a whole bunch of room to access this nut. My open end wrenches won't fit, but I have a small adjustable crescent wrench that worked. Remove both bolts.

The caliper should now pull off. The pads will probably stay on the rotor, and aren't fastened in any way (except possibly with a squeal-preventer compound, although my originals weren't). Pull the old pads out. Optionally, you can use squeal preventer as mentioned for front brakes. To install the rear pads, lay them in place on the rotor. They should stay there by themselves. Then try to place the caliper over the pads and rotor. This is easier than putting the pads into the caliper and installing the whole assembly. (For the front brakes, installing into the caliper first is the best way to do it, or only way to do it, considering the prongs that fit into the caliper piston in the front brakes.)

If the caliper won't fit over the pads & rotor, the caliper piston needs to be retracted, and the procedure is different than for the front. The back caliper piston doesn't push in, it screws in. You need to improvise a tool to do this. There is a slot on each side of the piston to grab with a tool and twist. (Screwing clockwise pushes the piston back into the caliper). Mine needed about half a twist or a little more. The tool I used was just a pair of needlenose pliers. I held the points open to fit the slots in the piston and after a little trial and error found a way to hold them to get the necessary torque. (It takes a fair amount of force and the piston should turn slowly and smoothly).

The rear pads have "spring" mechanisms on the back sides that fit between the caliper and the pads. Make sure that these are in the corrrect position (inside of the caliper) when you put the caliper on. It is easy to get the end of the spring poking out of the hole in the caliper, so watch out for this.

Reassemble. My new pads came with new attachment bolts. The bolts apparently have a threadlocker compound on them to keep them from falling out. You will need to use the double-pliers method again to tighten the caliper mounting bolts.

Do other side.

Before starting car and driving: Pump the brake pedal several times until it firms up and feels relatively normal. Check brake fluid level. Pump pedal again after starting car just in case. The pumping seats your loose pads against the rotor. (If the pads are loose and you drive off, you may be surprised by a brake pedal that goes all the way to the floor.)

Follow manufacturers recommendations for bedding in the new pads. My Ferodos were terrible for a while in stopping power. They needed a few dozen stops before they felt even OK. I have used other pads on other cars and they have felt fine right out of the box.

Good Luck!

Disclaimer: I make no guarantee regarding the above procedures and am not responsible for any brake problems, accidents, etc. "Don't try this at home."

New Information from David Banman (Mar-2001):

The article says: "If the caliper won't fit over the pads & rotor, the caliper piston needs to be retracted, and the procedure is different than for the front. The back caliper piston doesn't push in, it screws in."

This may work if you are replacing almost new with new. However, if your brakes are old/warn, this will not work. The correct tool actually requires a turning AND pressing to get the piston pushed back into place. The piston will not screw in without the special pressing tool.

Unfortunately for me I found out after my car was all apart...

To find an example of tool needed to compress the caliper, do this search and you will get a list of a few sold on the internet:

http://www.google.com/search?hl=en&q=Rear+Disc+Brake+Caliper+Tool&btnG=Google+Search

Note, many cars need this type of tool and thus these tools tend to be generic, but you may want to double check that the tool supports the A4 before ordering. This tool tends to sell for $60-90, so you might also check if your local auto parts store will rent you one.

New Information from Andrew Senko (Feb-2003)

For the rear brakes, the caliper bolt is indeed a 13mm bolt.  The nut that it attaches to is 15mm, but as others have said, you will need a thin wrench to get a hold on it.  I used an adjustable wrench that tapers at the end and it got the job done.

If you are replacing the rear rotors, you will also need a #8 (metric) allen head wrench.  After removing the caliper, there are two allen head bolts that need to be loosened so that you can remove the secondary bracket. After this piece is off the car, the rotor should be free.  I had to whack my rotors with a hammer to break them free from the car.

Others have mentioned the tool to retract the piston in the rear calipers.... RENT THIS TOOL!!  I struggled with every tool and method I could muster.  Out of desperation, I opened the yellow pages to see if I could rent the tool.  I got it for $8/day.  The tool did in 30 seconds what I couldn't do without it.

Standard disclaimers apply.

New Information from Ricardo David (June-2003)

Specifically having the proper tool to "reset" the rear brake pistons is key as indicated in the instructions. It is small investment that will repay itself over the life of the vehicle. Here is some more specific source information for the tool.

Official tool is VW 3272 available at www.zelenda.com for about $100

An alternative specifically designed for VW/Audi's is available for $40 -$45
This tool is availabe at www.germanautoparts.com and http://www.charterpa.net/cmeglio/metalnerd

P.S. I bought the tool from germanautoparts.com (adirondak) and it worked great