ts12345

I'm having this problem too on my front brakes (just replaced pad / rotors). Any word on how you fixed yours? Did bleeding the system fix the problem?

s4master1

Is this a 2.7 allroad? HP2 brakes?
If so, you have a problem with your master cylinder.
hard to explain why but we seen this a dozen times, cars coming back with brakes smoking and making horrible noises.
we noticed that cars with regular brake fluid service do not have this issue.
to avoid this we open the bleeder valves when renewing pads and flush out the hydraulic system completely.
try flushing the system first.

DJAllroad

I too am having this exact problem on a 2.7 Allroad. The further you try to drive it the harder the brakes lock up until the car will no longer move.

It was releasing itself over time until one day it would not. I had to have it dragged onto a flatbed tow truck and brought to the mechanic where it is currently sitting awaiting diagnosis.

I was leaning toward the brake booster being faulty as when you release the vacuum pressure there is a slight release on the brakes, however still not enough to drive the car.

The only difference on mine is that I had not performed any brake work on the car that would have caused this to happen.

Does your Brake pedal also get very hard and the booster not seem to activate giving you its assisting properties? My pedal would get progressively harder over about 3-4 KM and then you are stopped as the brakes slowly apply themselves.

Interesting take on this s4master1. I did read here somewhere that it is possible that the hydraulic fluid can absorb water over time as the fluid gets burnt/old and no longer holds its heat rating. Two possible things come to mind when I think of this. One: The fluid expands more than it should. If you retract the pistons, the fluid moves back to the resevoir. If the resevoir is now overfull it may be possible that the fluid can only expand out against the brakes as it heats up causing this problem. Two: corrosion or overall deteriation of the parts in the master cylinder;seals, springs etc. causing it to stick. As the master cylinder cools however it may release as it would contract. I guess this was common on older model Audis and pouring cold water on the MC would release them.

Glad I am not alone on this, I have never seen this happen. I have certainly had to drive with the E-Brake after losing brakes but not this.

I will update everyone as to the problem as it becomes known.

DJAllroad

I guess I should also mention that I think I do have the HP2 Brake as I have 8 pads up front.

ts12345

I do have the HP2 calipers.. and my car was doing just as DJallroad has described.. I was able to get the brakes to retract a little bit, but as I would drive they would just get more stuck again.

This lead me to call a local shop to try to get the car over there to have them look at it. On the way to the shop it got so bad that the car would barley move. To put the icing on the cake I had just painted the calipers as well (with caliper paint). When I pulled into the lot of the car shop the brakes went into flames!! The shop looked and said they think the paint is what caused the fire. (now i have a bone to pick with the paint company too)

So now I have my car at the shop and they are telling me it was the calipers the whole time (not the rotors or pads that i just installed, or the master cylinder) so they are going to charge me $2,500 to replace the brakes, rotors, and pads since they don't trust what I put on there. If this really is the master cylinder problem though, I'm thinking I might be better off just having the car towed to my house to fix myself. I bleed the brakes, but I did not do a full system flush... is that my problem?

I didn't think it was the calipers since they worked fine the day before i did the change..i was leaning to a master cylinder problem (since both calipers were acting up at the same time) which is what I was hoping the shop would look into before it caught on fire and made it look a lot worse than it probably was.

Thanks for the help everyone!

ts12345

My guess is the calipers probably need replacing now after the fire anyways.. any rubber seals must be melted right?

DJAllroad

Although it would be recommended that the Calipers be replaced, I would not have suspected that this is the source of our problem.
When your brakes locked up and caught fire, were all 4 wheels heated?

If so, I would not believe it to be the calipers. I have never seen 4 calipers start to stick mysteriously at the same time on their own just because you changed the pads and rotors.

On my allroad, all 4 wheels are locking and they got bad enough while I was trying to get it home they were glowing.

Here is a quick test that I was hoping to do but was/am out of town when it happened to my wife again. You can eliminate the calipers by opening a bleeder screw when the car is in this state. I suggest attaching a piece of tubing to the screw first to keep fluid from spraying everywhere, especially into your eyes.
If there seems to be lots of pressure on the line pushing fluid out, then there is a problem somewhere else in the system. You should also have this wheel released. If there is little pressure and that wheel does not release then it may be the calipers.

Also another reason to not suspect the calipers is that the brake pedal gets so hard. Calipers would not cause a hard pedal. Really this is the brake boosters job to provide assistance and ultimately provides the power behind the hydraulic fluid. If the booster gets stuck/malfunctions it may be sticking in the "on" position and not allowing the Vacuum system to help out or allow the master to retract.

I would not spend $2500.00 on it until they have checked the other systems for proper operation.

There are all kinds on things involved in our braking system. Booster, Master Cyl, Vacuum pump, ABS controller, etc...

I have removed the connector from my ABS controller with no change and also tested the vacuum pressure on mine.

DJAllroad

So after sitting at the Shop for the last two weeks, My mechanic finally looked at my Allroad and a great thing happened. The brakes locked on him in the parking lot.

He has told me that the Master Cylinder is bad and needs replacement. He removed the vacuum line from the booster and got sprayed with Brake fluid so the MC has now also started to leak or it has and I was unable to detect it before.

Anyhow, I have ordered a new one and it has arrived, Just waiting for him to put it on and see how it goes.

audiallroad2004

Did this fix the issue.. I am having the same issues with my 2004 audi allroad. When driving and the brakes engage (traction control or skidding)... the pressure just keeps building without releasing... and the car won't move.. until of course you bleed of a bleeder... and than you can drive it again. Also, if I disconnect the ABS/ ESP fuses, than it will work without the abs active or stability control.. will changing the master cylinder fix this problem from your experience?

DJAllroad

Hello there,

We’ll this is an old thread so I’m glad I still got notified of your reply. I have long since sold this car but yes, replacing the master cylinder was the fix in my case. When I got the old one back I tore into it and it looked like the plunger inside had bent somehow. With enough time it would release some pressure but would of course go back at the first press of the pedal.

Since you see a change by removing fuses there must be some other issue there as my issue was not electrical or electronic related.

I would lean towards a failure in the ABS pump on this one. One way to test as well would be to release a brake line at the master cylinder when this happens and see if there is pressure there. Likely you won’t find any. Then release one on the wheel side of the ABS pump and if you now find pressure the ABS pump is holding the pressure and not the master cylinder.

I hope you can come to the source of your issue soon.