Guide: Rear Brake Caliper Piston Rebuild

[M-A8]

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

[MatthewH]

Originally Posted by M-A8

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.

[onetwentie]

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.

[Johnmed]

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.

[MatthewH]

Originally Posted by onetwentie

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.

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.

Originally Posted by Johnmed

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/

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.

[dangerdred]

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?

[NightOwl]

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.

[dangerdred]

Originally Posted by NightOwl

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.