reesea17

So I'm driving along and all of a sudden the car starts feeling like it is braking on its own; it becomes a struggle to get through the car keeping pressure on the brakes while I'm 30 ft from home. Get the car in the garage, jack up the rear wheels and the rear right wheel will not budge.

I assumed that it was a seized caliper and elected to replace it with a remanufactured one. Finished installing the new caliper, bled the system and then tried to drive the car.. won't budge, wheel is still locked and it felt like there was more. So I jacked up the car and find that the Front drivers side wheel will not move, nor will the rear right that I just replaced.

I'm not experienced enough with this so I'm hoping someone here can help me out. Haven't been able to find too much on the brakes staying engaged yet. I'm starting to think that it could be the master cylinder? Or something to do with the ABS? where the pressure is allowed to build up in the system but not allowed to bleed out..

Any ideas? Appreciate the Help.

TheHud85

Dumb question: Have you tried pulling up on the brake pedal to see if it's sticking? Is it low?

plat27265

The symptoms you described happened to my old Isuzu IMark years ago. The rear brakes locked while I was driving. My rear brakes were emitting white smoke (ahh, the smell of asbestos!) as I tried to make it to my mechanic's garage. Turns out, the brake master cylinder piston had a tear. It was rebuilt using a generic replacement part a few days ago. Had to rebuild the master cylinder again using better branded part. I suspect you have a bad master cylinder.

reesea17

Doesn't have anything to do with the pedal. It's been returning after each depression.

reesea17

My main feeling is that you are correct.

From my understanding there are two types of master cylinder set ups out there, one where the front and rear wheels are on their own pressure "bank" if you will, and one in a diagonal style where the front right and rear left/front left and rear right brakes are connected on the same "bank". I believe my Audi is set up in the latter configuration.

After posting this question I went back to the car, took the right rear wheel off (the one I had just replaced the caliper on) and loosened the bleed screw on it. Lost a little fluid and could hear the pressure being released from the brake. Put the wheel back on and it spun freely. Jacked up the front left wheel and it too spun freely. So I'm currently waiting to get a new master cylinder and hoping that that will solve my current problems.

massboykie

Could it be the ABS pump that's freaking out? Engaging the rears only for some reason? You should be able to check that with VCDS to confirm. Maybe try turning off the ESP and / or pull the ABS fuse?

Probably a long shot but I figured it may have something to do with it.

Cheers
Massboykie

Prospeeder

Its rare, and especially rare on cars this new. But brake hoses can fail, the inside comes apart, and acts almost like a check valve, and holds hydraulic pressure. If you opened the bleeder, on only 1 wheel, and it had pressure. I would bet the rubber hose there is bad. If its at every wheel. You may want to look into the booster come apart inside and holding the master depressed slightly, bad master, or even something crazy with the ABS, but I havent seen that.

reesea17

I'm currently in the process of replacing the master cylinder. That lower T45 bolt is a bitch and a half if you don't have a ~1 in or less long T45 bit.

One of the observations I didn't necessarily mention before is that when I had released the pressure at the rear right caliper, I heard the pressure being released in almost a bubbling sound. Not really sure if that means anything. But I'll finish up this master cylinder replacement and then get on to bleeding the entire system.

Prospeeder

Be sure to carefully inspect the inside of the booster. if you can reach in and pull the booster pushrod out, the booster is bad! If you see any pieces or parts laying inside the booster, its bad! If the booster is full of water which is actually common on Passats and A6's, its defiantly bad lol.

reesea17

So, could you see the brake booster failing, and if so what would that cause? Only thing I can find online is that some people experience boost issues with a failing booster. The bottom left 22mm bolt holding the master cylinder on to the booster had a good amount of rust on the base of it.

The only one write up with pictures I could find referenced the same issue and attributed it to what his problem was with the booster allowing water in. Mine is not full of water, looks like some may have been in there at some point, but it was dry.

Bottom line is, would this cause my problem though? With the front left and right rear wheel locking down tight and not releasing the pressure? I'm afraid I'm going to get through this master cylinder replacement only to have the same issue and not know where to go other than possibly the brake lines themselves and the ABS module possibly. But that's where my inexperience/lack of knowledge pushes me. Could this be attributed to the booster as well? I can post photos as well if that helps.