Guide: Rear Brake Caliper Piston Rebuild
 

Rear Brake Caliper Piston Rebuild

As I've mentioned before, I've been having some trouble with my rear brakes seizing. The sliding pins were fine, it turned out to be a sticking piston.

Replacement calipers are expensive even without the EPB motor, so I decided to strip mine down, clean it up and replace the seals.

The Audi part number for the seal kit is: 3D0 698 671 (around £20 inc VAT, this contains replacement seals for both sides)

Firstly, remove the EPB motor from the caliper (2 torx screws) and set it aside. The electronic connector doesn't need to be removed. Remove the caliper from the car and undo the brake line.

http://picoolio.net/images/2017/02/0...445181a023.jpg

The brake line will continue to slowly drip fluid while the caliper is off the car, so it should be blocked somehow. Some people use grips to compress the rubber hose but I don't really recommend this.

http://picoolio.net/images/2017/02/0...50648e29c8.jpg

I happened to have a spare caliper indoors so I temporarily attached it the brake line.

http://picoolio.net/images/2017/02/0...51837bc9d2.jpg

Ensure all brake fluid has poured out of the caliper before taking it indoors. (preferably into a container!)

http://picoolio.net/images/2017/02/0...517563a8bc.jpg

The piston is now ready to be removed from the caliper. On most cars, compressed air is generally used to pop the piston out. However, as we have the electronic handbrake, we can easily remove the piston by hand. Use a torx T40 key to turn the gear on the back of the caliper anti-clockwise. This simulates activating the electronic handbrake and pushes the piston out.

http://picoolio.net/images/2017/02/0...52407409b4.jpg

Also, if you don't have a T40 key, there is one included in the Audi toolbox in the boot :)

http://picoolio.net/images/2017/02/0...525496d57c.jpg

As there is no disc brake to stop the piston from travelling further, it will eventually pop out.

http://picoolio.net/images/2017/02/0...526262e1fb.jpg

The large dust boot on the piston can now be removed as this will be replaced. Clean up the piston and remove any dirt - I used a kitchen scouring pad. You don't want to use anything too abrasive as this could affect how well the piston seals in the cylinder.

http://picoolio.net/images/2017/02/0...7594187e3c.jpg

Remove the inner o-ring inside the caliper. I used a small flathead screwdriver but be careful not to damage the inside of the cylinder. Also ensure the inner bore is clean.

http://picoolio.net/images/2017/02/0...53051c03f4.jpg

The caliper is now ready for new seals. Unbox your Audi seal kit - this should contain 2 sets of seals and a bag of red fluid. The new seals must be soaked in this fluid for around 1 hour before use.

http://picoolio.net/images/2017/02/0...4083887096.jpg

When the seals are ready, fit the new o-ring inside the cylinder and ensure it is correctly seated all the way around.
Coat the piston surface in this red fluid and fit the new dust boot in the following position:

http://picoolio.net/images/2017/02/0...02327b29b2.jpg

Fit the bottom of the dust boot into the caliper. The bottom of the dust boot contains a thin ridge that sits inside the caliper bore.

http://picoolio.net/images/2017/02/0...02500a4fe1.jpg

The piston is now ready to be pushed back into the caliper - this is the hardest part! It must be pushed in at a perfectly straight angle otherwise it'll get stuck. I used a G-clamp to centre it and push it back in - if the angle is correct it will require very little force.

http://picoolio.net/images/2017/02/0...0365452338.jpg

By pushing the piston all of the way in, the top of the dust boot should seat itself correctly on the piston. Push the piston in and out a few times to ensure everything is seated correctly.

http://picoolio.net/images/2017/02/0...04030ffe40.jpg

The caliper is now ready to be refitted to the car. Remember to bleed the brakes.

http://picoolio.net/images/2017/02/0...31726f3ca9.jpg

The electronic handbrake will need to be cycled a few times to allow it to readjust before driving.

Brilliant write-up. Thanks for posting it! +++

Well done mate and good work +++
I will add this to my second To Do List.

I see you have ceramic brakes (assuming you're taking about the S8 in your signature) - make sure you have the same rear caliper setup as those of us with standard brakes before ordering the seals! I'm not familar with ceramic brakes but they may be the same.

Let me know if they do turn out to be a different setup - I should be able to find a suitable kit.

MatthewH..

Hat off to you sir! what a guy!

That was not just a spectacular attempt at something which the dealers would, (and indy's have ripped me personally a new rear end for); but also an excellent write up.

One of my rear calipers died on me a few years back and I ended up paying an indy circa £1200 for the fix (including a new EPB module), incidentally the EPB is throwing errors again, and it doesn't work (if you activate it, you get no end of alarm bells going off in the car, which take a while to stop bleeping) - so I just don't use it.

The rear pads are now in need of replacement, so I wonder if I will end up having to do something similar.

A few questions:

When you remove the brake line, doesn't that assume that brake fluid will just pour out? or would that only happen if the brake pedal was depressed?

Also, when you say bleed the brakes, do you mean to remove some of the old brake fluid and top up with more, in order to remove any trapped air?

thanks again for your post - I found it very useful!

ps - what were the initial symptoms? you mention sliding pins? not familiar with these - would love to hear more on this.

Well done Matthew. Pat yourself on the back and pour yourself a beer. I contemplated going down this route when my calliper's piston seized a while back, but took the easier route of buying a refurbed unit from ECP for around £170, after exchanging mine.

I used one of these (or similar) from Machine Mart to help with retracting the pistons:

https://www.machinemart.co.uk/p/lase...e-wind-tool-s/

My symptoms were warm wheels (NSF and OSR), the NSF just needed the pins cleaning and greasing.

Hi,
The brake fluid will slowly drip out when the caliper is removed but nothing major. You could probably clamp the hose to prevent it from leaking out. I had a spare caliper I connected to keep it sealed.

Yes, the brakes must be bled from the bleed valve after changing the caliper as there will be "air gaps" in the pipes/piston.

The sliding pins are shown on the first photo - they hold both parts of the floating caliper assembly together (like rails). The pins must be kept greased otherwise they can seize up and prevent the caliper from moving in and out freely.

Thanks. I also have one of these but it didn't come with the correct attachment for the A8 pistons. A cheap G-clamp seemed to work well as the piston doesn't need to be turned while it's being pushed in once the piston has been fully wound in from behind.

Apologies for the thread resurrection.

Does anyone know if following the OP method above and manually winding the piston in as described, after reassembling, is the EPB module able to figure out what the piston position should be? Is it just a case of putting it all back together and then doing a function test and it will all just settle down correctly? Also, is there some sort of gasket or seal between the motor housing and the caliper?

I've only done this with VCDS, and have never had any problem after cleaning and replacing seals on the rear caliper. Would like to think though, that cycling the hand brake would do the trick too. Between the motor and the caliper, there is a O-ring with parts number 4E0615137.

Ah nice, thanks for that. I've bought two new rears at this stage and have two spares that I'm hoping to eventually refurbish - up to now I was gonna reuse the old o-rings.



Is it a thing on these cars that the rear caliper gets dogs abuse with caliper pistons getting corroded? - Replaced OSR caliper at 130k and now NSR at 140K.