Binding brakes

[oscar21]

B8.5 2012 2.0TDI quattro RHD

Ever since I've had this car I've had trouble with the brakes sticking. Firstly it was one of the rears but the calliper was actually seized so I changed it and all was well for a while, then occasionally the front brakes will drag slightly just for one journey and once they have cooled down again they seem to be ok for a while.

Most recently though the front left brake has been binding and once it gets warm its even worse, to the point that the disk is steaming hot after a few miles. So today I changed the calliper and went for a drive, the left front is now ok but the front right has started binding whereas before that one was fine.

when I dismantled the old calliper it did seem a bit stiff to push in with the rewind tool but I've taken the piston out and there aren't any score or rust marks marks on it and it now slides in and out freely. Is it worth changing the other front calliper and see what happens, I used a pump up bleeder to get the air out of the new calliper and I'm pretty confident I've done it correctly.

 

[spartacus 68]

Your car is the same age as mine. I chose to rebuild the brakes on my Allroad last year. I had a binding rear caliper and a bit of heat from the front caliper too.
You might not have seen any corrosion on the caliper piston, but where the issue is - is corrosion forming under the rubber dust sleeves. This corrosion forces the rubber dust seal to effectively stop the piston from retracting.

With the caliper off, you can do a full strip down and rebuild. Good opportunity to wire brush the carriers (wire wheel on drill attachment) and inspect the brake sliders. I used Budweg brand from Autodoc. Audi still do the front repair kits, but won't even supply the rears - but they will sell you a replacement caliper instead!

I couldn't fault the Budweg brand. Comes with dust seal, square seal for caliper piston and new rubbers for the brake sliders. On the rears there are 'O' rings.

Grease wise, use a little red grease on the piston and rubber sleeves, and ceramic paste on the sliders and pad contact points.

It took me a few attempts to bleed the brakes properly. When you are dismantling the calipers, you can either use a tool to compress the brake hose (not everyone approves of that) and close the reservoir cap. If the brake nipples look past their best - renew them too. The best brake bleeding is to get someone to pump the brakes. You see exactly what us coming out in terms of bubbles on each brake cycle. I have a Draper Brake fluid kit that pressurises the brake fluid and keeps it topped up.

On the rears you ideally need VCDS with the electro-mechanical handbrake, but it is possible to bypass with a battery. Check out Dave Sterl videos on YouTube.

 

[oscar21]

Your car is the same age as mine. I chose to rebuild the brakes on my Allroad last year. I had a binding rear caliper and a bit of heat from the front caliper too.
You might not have seen any corrosion on the caliper piston, but where the issue is - is corrosion forming under the rubber dust sleeves. This corrosion forces the rubber dust seal to effectively stop the piston from retracting.

With the caliper off, you can do a full strip down and rebuild. Good opportunity to wire brush the carriers (wire wheel on drill attachment) and inspect the brake sliders. I used Budweg brand from Autodoc. Audi still do the front repair kits, but won't even supply the rears - but they will sell you a replacement caliper instead!

I couldn't fault the Budweg brand. Comes with dust seal, square seal for caliper piston and new rubbers for the brake sliders. On the rears there are 'O' rings.

Grease wise, use a little red grease on the piston and rubber sleeves, and ceramic paste on the sliders and pad contact points.

It took me a few attempts to bleed the brakes properly. When you are dismantling the calipers, you can either use a tool to compress the brake hose (not everyone approves of that) and close the reservoir cap. If the brake nipples look past their best - renew them too. The best brake bleeding is to get someone to pump the brakes. You see exactly what us coming out in terms of bubbles on each brake cycle. I have a Draper Brake fluid kit that pressurises the brake fluid and keeps it topped up.

On the rears you ideally need VCDS with the electro-mechanical handbrake, but it is possible to bypass with a battery. Check out Dave Sterl videos on YouTube.

Thanks for the reply, funny enough I watched a Dave Sterl video by chance over the weekend after I had changed the caliper and he was going on about the dust seal retaining clip rusting and jamming the calliper so it could well be that. The new calliper I got was only £35 off ebay, I can imagine they arent the best quality going but the one I put on the rear a couple of years ago is still fine it seems so I've ordered the drivers side front one and will change that this weekend.

As for the rear brakes the first time I changed the rear pads I took the motor off them and wound the handbrake mechanism back with a star drive but I found it much easier just to connect a battery to them as you say. People say they need calibrating afterwards to reset them but I don't think that is the case at all, there are only two wires going to them that get the polarity reversed depending on if they are opening or closing so the system must monitor how much current is being drawn by the motors as they clamp down, the harder they clamp the more current it will take so when a pre-determined current is reached it cuts the power..

On the last point about bleeding the brakes I have always used the pedal pump way with a glass jar but the last car I did was my friends C class merc and we just couldn't get a pedal or even any fluid to come out of the bleed nipples really doing it that way, we had to use the pump up pressure thing like you have and pump it up to the point I thought it was going to explode before we finally managed to get the fluid to flow to the callipers and then everything was fine.

 

[spartacus 68]

This is on an A5, and yes the retaining clip which is integral to the dust boot has gone. I run a Volkswagen Polo daily driver too, so some of the dust boots use a internal recess on the calliper bore to engage, where as the A4 one clips over the main body.

Here’s the video.

 

[g00se]

You can buy my S4 front calipers if you like... they've never had an issue

Ad is in the classifieds section

goose

 

[oscar21]

I've now changed 3 callipers on my car (the 4th was done a year or so ago) so they are all new now really and I think the binding has stopped for now at least. However the pedal still feels a bit spongy to me although the brakes seem to work ok.
I bled the brakes by connecting a pressure bleeder to the reservoir and pumped it up to about 20 psi. then opening the bleed nipple with a hose attached into a jar of fluid. Even with 20 psi the fluid was reluctant to flow out of the nipple, especially on the rears. I then tried pumping the pedal and holding it down with a bar against the seat whilst I closed the bleed nipple and that certainly filled the jar up with fluid so the air must be out of it by now right?

What I don't get though is when you pressurise the pump doesn't all the air in the tube and the reservoir get forced into the system when its under pressure compounding the problem? and does the ABS module cause problems when trying to bleed the system

Finally I might have to get a 2nd person to pump the pedal whilst I open and close the bleed screw and see if that works. And finally just to make life worse I found a broken spring on the rear so that needs replacing as well now.

 

[spartacus 68]

To be honest, these pressurised brake bleeders are so-so. Grab a member of the family (or a good friend) if they say no and get them to help. Keep the reservoir topped up as you bleed it so you don’t draw in air. You can run the engine too. Furthest corner from the reservoir in sequence. Make sure the tube is transparent so you can see the fluid and possible air. The old fluid is likely discoloured and has moisture in it.

The rear spring is hard work on an avant, not sure if your one is a saloon? Dave Sterl video is good. Remember and change the rear spring rubber seats while you are there..

 

[GC001]

Just logged in due to my 2012 binding its front brakes; this has answered my questions!

 

[oscar21]

right I think its safe to say after a few days of driving the brakes are normal again. doing the pedal pump method of bleeding certainly worked a lot better than the pressure bleeder way. Just got to tackle the spring next.