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Rebuilding HP2 Brake Calipers - Audi A4/S4

Prior Experience: Perhaps a little
Cost: approx. $30
Time: aprrox. 2 hours

Discuss this mod - Here

Additional discussion on this mod has taken place Here

I have been running the B5S4 HP2 brake calipers on my A4 for a couple of years now. Unfortunately, I have not been driving my car very often and it more or less sits in the garage for a large portion of the year. When I took it out of the garage this year, I noticed I had some really bad shuddering while braking. When I checked out my brakes, I saw some terribly uneven brake wear.

The thought was that my calipers were sticking, so I decided to break them down and rebuild them to bring them back to life. Here is how I did it.

B6 Audi A4 - Caliper Rebuild   B6 Audi A4 - Caliper Rebuild
Before      After
 

SUPPLIES - Supplies are simple...some basic hand tools, a wire brush, caliper grease...etc

B6 Audi A4 - Caliper Rebuild  
What
Caliper rebuild kit (new seals, etc - $20 each caliper at ECS Tuning)
11 mm wrench
T-? Torx Wrench
T-? Torx Wrench
X mm "Triple Square" Bit
Small Needlenose Pliers
Ratchet
10mm socket
21mm socket
Access to air compressor
 

The first thing you need to do is remove the calipers. I wont cover this here as it was already covered in the B5S4 caliper upgrade. It is very easy to remove the calipers - it is essentially 2, 21mm bolts on each caliper and then the connection for the brake line. Follow the other write up for more information.

 

Just for your reference, the 'odd brake wear' I was seeing looked like this:

The inside pads were just fine (so of course my brake wear sensors didn't detect anything), but my outside pads were completely gone. This was happening on only one caliper - the other three corners looked perfect.

 

B6 Audi A4 - Caliper Rebuild

 

The first thing you want to do after you remove the calipers is back out the bleeder screw so that you can push the caliper pistons back into the calipers. Pushing the pistons back will push most of the fluid out of the calipers - catch it in a cup or something similar

NOTE: Some fluid may shoot back out of the line - be sure to wear safety glasses so you don't get splashed.

  B6 Audi A4 - Caliper Rebuild
 
With the bleeder screw out of the way, you want to use your triple square bit to remove the bolt shown to the right. There are two of these bolts on each caliper - remove them both.   B6 Audi A4 - Caliper Rebuild
 
 
B6 Audi A4 - Caliper Rebuild  

When you get those two bolts out, the calipers will come apart like this

 
The two metal rods are the guide pins for the calipers. The calipers should be able to slide freely on these two guide pins - if you see anything wrong with these (bent, etc), then you have found a problem. The surfaces of these pins should be smooth - if there are nicks, or if they are marred, you will have use some emory cloth to knock the rough spots down. Ideally you should replace them, but unfortunately, I could not find them sold separately for the HP2 calipers. Here are what mine looked like - no discernable problems (sorry the pics are a bit blurry)
 

B6 Audi A4 - Caliper Rebuild

  B6 Audi A4 - Caliper Rebuild
 
If all looks well with your guide pins, or you think you can recover them, then you should continue breaking down your calipers. At this point, you should be able to pull the caliper apart into their 3 main pieces   B6 Audi A4 - Caliper Rebuild
 
The next step is to get the pistons out of the calipers. If you have a single piston this may be easier - it can be a bit tricky with the dual piston setup.

In order to remove the piston, you will want to blow compressed air into the bleeder screw hole - this will push air behind the piston and one (of the two) pistons will pop out. CAUTION: the piston WILL fly out - because of this, you should hold the caliper about 3 inches off of the table with the piston aiming towards a table. This way when it comes out, it is stopped by the table. You DO NOT want the piston to fall off the table onto the floor - you could damage the piston and ruin the caliper.

Here you can see I have the pistons pointing towards the table. Also, YOU BETTER HAVE ON SAFETY GLASSES. The remaining fluid WILL shout out of the brake line as you do this!

  B6 Audi A4 - Caliper Rebuild
 
Here is what the piston and cylinder look like when the piston comes out:
B6 Audi A4 - Caliper Rebuild   B6 Audi A4 - Caliper Rebuild
 
After you get the first piston out, you may be scratching your head on how to get the other one out. What you need to do is put your finger inside the cylinder of the piston which just popped out, and block off the air/fluid passage between the two pistons. Then blast the compressed air into the caliper from either the bleeder screw hole or though the brake line - whichever one is closer to the piston which is still in place. You will understand what I am talking about when you see it.
After you get the pistons out, you want to remove the dust boots from each of the cylinders. They are simply pressed in place. There is a lip around the inside edge of the cylinder that you can pop them out of   B6 Audi A4 - Caliper Rebuild
 
With the dust boot removed, you can now remove the pistons seal. It is just a ring that goes around the cylinder - once again it is just press fit into place. You can use a pick to pop it out. Here is an image of it (picture is taken after I got the calipers powder coated)   B6 Audi A4 - Caliper Rebuild
 

Part 2: Additional Teardown for Powder Coating

Since I had the calipers torn apart this far, I decided to keep going and to get them powder coated. In order to get them powder coated, you have to remove all of the parts that you don't want coated, and the parts that would be damaged in the process. Here's is how to fully tear the calipers down

First you want to remove the hardline from the caliper - and then the bracket which is holding the brake line to the caliper. You will need an 11mm wrench for the hardline, and I believe a 10mm socket for the bracket bolt

B6 Audi A4 - Caliper Rebuild   B6 Audi A4 - Caliper Rebuild
 
The only thing left to remove on this part are the two black guide pin bushings. In order to get those out (I don't have pictures) you just spray some WD-40 or other lubricate on them and push them out of place. It takes a bit of effort, but they pop out without any special tools.

Next, you want to remove the pad retaining spring. In order to do this, you first remove the small Torx bolt that was located at the circle in the picture to the right. You then want to push the retaining spring out. To help with this, you can push a small pick in through the backside and push the retaining spring out of place.

It should pop right out.

  B6 Audi A4 - Caliper Rebuild
 

The final part of the breakdown is removing the dust boot that is shown to the right. Its removal is not very obvious. There is actually a metal retaining spring around the boot which is holding it in place. In order to remove it, you can use a flathead screwdriver or something similar and pry it up from the bottom. Slowly work your way around the boot being careful not to pry against the rubber.

There are other ways to do this, they are discussed in This Thread. You may want to read that before continuing.

Once again I took this picture out of order.

  B6 Audi A4 - Caliper Rebuild
After you have them completely torn down, its time to clean them up and put them back together.

Part 3: Rebuilding the Calipers

As I mentioned previously, I decided to get the three main pieces of the calipers powder coated. The rest of the parts I decided to clean up on my own an to paint.

The simplest way to clean these types of parts is to use a wire brush attachment on a die grinder or hand drill. This can quickly remove rust and other grime to bring a nice shine back to your parts

You can see a before and after of the brake line bracket to the right - 2 minutes of work and the parts looks new again

  B6 Audi A4 - Caliper Rebuild
 

B6 Audi A4 - Caliper Rebuild

 

You'll want to go ahead and do this to all of the parts that you will be painting. This is a quick way to clean them up prior to paint.

 

I'm not going to tell you how to paint them - you should be able to do that on your own. Just be sure to use some high temperature paint - I used some silver and black engine enamel.

 
When I got my parts back from the powder coater, they looked like this:
B6 Audi A4 - Caliper Rebuild
 
FYI, I got the 6 main caliper parts sand blasted and powder coated for only $70. The place I used was H&H Powder Coating and I couldn't be happier. They did a great job, had a quick turn around and were cool to deal with. They are local to me so obviously I didn't have to pay shipping - but if you are getting quotes much over $70, you may want to consider shipping the parts to these guys. My first quote was $190 which is way too high for something like this.
 

Here is a closer shot of the parts I wire brushed and painted - not too shabby.

  B6 Audi A4 - Caliper Rebuild
 

Now that you got your parts back, you can drool over them for a bit, and then get back to rebuilding the calipers. You want to assemble them in a very clean environment - I moved inside the house an a clean table to do this work. You don't want any dust or grime inside your calipers!

Here is a picture of the brake caliper seal kit - it is an OEM part so you can get it from any dealer. I got mine online for about $18 per caliper.

Each of the HP2 calipers require 2 dust boots and 2 piston seals

  B6 Audi A4 - Caliper Rebuild
 

You start by putting in the piston seal. You should dip it in some brake fluid before you insert it into the caliper. This will help it make a seal, and make installing the piston easier.

When you look in the cylinder, you will see the cutout for the seal - just pop it in place. This seal is all that is keeping your brake fluid behind your pistons and in your calipers/brake lines. Be sure to push it in place properly so it is not damaged when you insert your pistons

B6 Audi A4 - Caliper Rebuild

  B6 Audi A4 - Caliper Rebuild
 
The dust boot is the same type of deal. There is a lip around the bottom of the boot, and around the top of the cylinder. You just need to line them up and pop them in place. Work your finger around the edges to secure it in place.

B6 Audi A4 - Caliper Rebuild

  B6 Audi A4 - Caliper Rebuild
 
 

The piston can be a bit of a pain in the ass to get in place. You should first dip the piston in brake fluid, and then try to slide i past the dust boot. It may help to get someone else to pull the dust boot open while you try to fit the piston into place. I did 2 with a second set of hands, and 2 by myself. It can work either way.

After you get the piston in place, push it all the way in. When you push it in, the dust boot will secure itself around the upper lip of the piston.

B6 Audi A4 - Caliper Rebuild

  B6 Audi A4 - Caliper Rebuild
 
Repeat the above process for the remaining pistons.

For the rest of the assembly, you will want to use caliper grease on any of the remaining moving parts. You can pick this stuff up at any auto parts store.

  B6 Audi A4 - Caliper Rebuild
 

Next you will want grease up this joint and reinstall the boot. As before, the boot has a metal retaining ring around it. In order to get it in place you can just use a flathead screwdriver to work around the edges from the inside of the boot.

Also, you could use a socket to pus it into place

  B6 Audi A4 - Caliper Rebuild
 

Next you want to reinstall the guide pins and their boots. You want to grease up the guide pins real well before installing them.

Don't worry about putting on too much grease, you can always just wipe off the extra.

  B6 Audi A4 - Caliper Rebuild
 
Realistically the rest of the assembly is exactly the reverse of the break down. I won't show pictures of each step. You can refer to these photos as a reference of the orientation of each part - make sure you get it right. Here are pictures of the final products.

B6 Audi A4 - Caliper Rebuild

  B6 Audi A4 - Caliper Rebuild
 

B6 Audi A4 - Caliper Rebuild

  B6 Audi A4 - Caliper Rebuild
 
That's all there is too it. Good Luck!


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