So everyone who knows anything about rebuilding calipers knows that rear calipers with an integrated parking brake mechanism are a huge PITA to rebuild. After reading many write-ups I decided to give it a shot.

Unlike any of the pictures I've seen online, I discovered that on my 2000 A4 the shaft, cap, spring, and washers are actually installed as a single unit. The cap has tabs that wrap around the alingment washer at the bottom (see pic). So if you are doing this and manage to get the retaining ring out (which is the hardest part by far), don't be surprised when the internals of the caliper don't just fall out. You need to unbolt and remove the bracket from the back of the caliper, and then carefully hammer the shaft in for everything to come out from the inside. I used a drift punch as to not damage the threads.

That looks a lot like the S4 calipers I started to rebuild (but ended up trashing due to stripped bleeder screw threads).

What did you use to get the retaining clip out? I used this:

Also, the assembly inside the piston comes out as well, with a similar retaining clip. If you buy a full rebuild kit it will come with a bunch of random O-rings, and one of them will go on a shaft where the assembly inside the piston meets the piston.

Also, I have found no rebuild kit that is 100% complete for the B5 A4. The first 2 kits below from RockAuto have the correct piston seal/boot and O-rings, but they include extra parts that aren't needed. Perhaps they are for FWD? (The Carlson part says "Base Model" but the Dormarn part does say Quattro, I think that's wrong). The third kit does not have the extra parts, but most importantly none of these kits have the seal for where the shaft exits the back of the caliper and connects to the cable bracket. The failure of this seal is the reason for the parking brake mechanism getting contaminated and binding up. If you look at the pictures, the first 2 appear to have seals that might work there, but they are not even close to correct.

More Information for CARLSON 15082
More Information for DORMAN D351808
More Information for CENTRIC 14333007

I did discover that the B5 S4 kit by Centric does include this seal, however the piston seal/boot are larger on the S4. You can see the required seal in this pic that is missing from the others.

More Information for CENTRIC 14333016

I got lucky in that I had those seals left over from when I only did a partial rebuild on my S4 calipers. That is, if owning 2 B5 Audis that are always broken can be considered lucky...

So in summary, if you need to rebuild a B5 A4 rear caliper due to the parking brake mechanism binding up, you will need to buy both Centric 143.33007 and 143.33016. They're only $3 each so who cares... remanufactured calipers would be much easier but at $90 a piece.

I saw that tool too and was going to buy it but first I decided to try this.

5-3/4" Needle Nose Pliers

Those pliers are TINY. I was able to file the ends into small points in a matter of seconds, honestly. Then I carefully bent the handles away from the joint. It is not a 90 degree bend like the Motion Pro tool, but its about 30 degrees which is enough to get the job done. Even with the integrated spring/cap unit, you still have to compress the spring slightly to get the retaining clip out and back in unfortunately.

And yes I replaced the o-ring in the piston as well. See my reply regarding the rebuild kits and how they are missing parts.

If anyone is curious, here is the tool I ended up using, shown next to standard needle nose pilers and retaining ring pliers for size comparison. You can see how the handles are bent, which allows clearance from the caliper to get down into the cylinder.

I don't really have a problem with buying $25 tools that I will very rarely use, I have tons of those. But since Harbor Freight is literally around the corner from my house, I have started to make modified tools in some situations if I can come up with an idea that might work.

We appreciate your efforts on the DIY, but I realized a while ago its probably more cost effective to buy remanufactured calipers from AC Cardone or something and then returns the originals as core.

A caliper will run you around 70-100 dollars for the rear and like 50-90 for the front I believe.

You did good though.

Be sure to let the new seals soak in clean brake fluid prior to reassembly.

Looking at the condition of the caliper bodies, you may want to have them cleaned with high-pressure solvent to remove scale and any outside corrosion. Clear coat or paint can preserve the metal from further corrosion, but may lead to increased heat retained in the caliper under heavy braking conditions.

Some people think painted calipers have an appealing look through the road wheel, so I imagine it is a personal preference of sorts...

The rear B5 calipers are actually quite simple to rebuild, once you're familiar with their design. I can't speak for the B5 A4 specifically, but I bet I could rebuild a pair of rear B5 S4 calipers in about 2 hours or less once they are off the car (provided nothing is seized up).

Total cost of rebuild parts (again, assuming nothing is seized and the pistons are still useable) for TWO S4 rear calipers is $58 including the rebuild parts for the caliper carriers. Take that and a few hours and you can save yourself $100 compared to buying rebuilt ones. To each their own, of course.

But if the housings are screwed then it's definitely better to go the route of buying rebuilt ones and exchanging your cores...