Audi Allroad brakes - pulling, no feel, faulty circuit

[allan_audi]

Hi,

Can anyone help re: Audi Allroad brakes.

Problems started a while ago when right hand front caliper seized (pistons were stuck) and brakes started to lose feel.

I fitted new caliper, and overhauled the rest. Bled the brakes over an over again, even used VAGCOM to run the pump, but still it had the lack of feel and pulled to the left.

Finally today got round to fitting new master cylinder, bled again and again with VAGCOM, pressure bleeder, even directly on the pedal, but I couldn't belive the brakes were exactly the same.

While it was up on ramps, I wedged the brake pedal, to the point where the brake lights come on. I was confused, I could move the front right and rear left (same circuit), but the other two, front left and rear right were biting. Apply further pressure and you could start to feel the other circuit starting to work, but the others would be locked. The circuit does eventually lock too, but not at the same time.

I know all the calipers are free, even the slide pins.

It seems the original caliper seizing may have been a symptom of something else failing.

Anyone have any ideas? Please help! I need to be sorted, as it seems to be getting worse.

[Columbo]

Is it an Auto or manual?

If it's manual you need to bleed the clutch cylinder first, then the brakes.

Bleeding sequence
1 - Front right brake caliper
2 - Front left brake caliper
3 - Rear right brake caliper
4 - Rear left brake caliper

Aparently there are two typres of ESP unit 5.3 and 5.7.

5.3 needs a pressure of at least 2 bar is required for bleeding the ESP hydraulic unit. Therefore always check the pressure setting on the bleeding device.
First, all of the brake calipers are bled using the conventional method.
Afterwards the ESP hydraulic pump needs to be bled. This is done using vagcom
Vagcom is used to actuate the hydraulic pump for 10 s.

Unlike ESP 5.3, ESP 5.7 does not incorporate hydraulic pump -V156. Therefore it is not necessary to bleed the system with the diagnostic tester.

Taken from service manual. Hope this helps.

[allan_audi]

Thanks, but I've used the correct bleeding sequence from ElsaWin, I always use the tyre to pressurise the system, so about 34PSI, which I think is more than enough. I suppose I could be losing pressure during the bleeding. I've run the ESP pump up too. I've tried te complete procedure several times but with no difference.

The trouble is I would expect if the problem was air then the brakes would "pump up", to the point where they're working properly but they don't.

Anybody have any other ideas?

[lonky]

Auto bleed kits always say to lower the pressure to 1 bar - 15psi in the tyre.

This is done so as not to damage the storage tank, and when it presurises it can blow air through the fluid which totally defeats the object of the exercise.

[NickPicks]

Auto bleed kits always say to lower the pressure to 1 bar - 15psi in the tyre.

I'm pretty sure Elsawin states that aswell.

[allan_audi]

Elsawin quotes "at least 2 Bar" so around 28PSI, a few more PSI is not going to harm.

Anything less than that and the fluid hardly moves, especially the rear calipers.

[allan_audi]

I decided to remove my ABS Modulator block and send off for test/repair. I removed the whole frame including return pump, I was amazed to find this pump full of old dirty fluid, despite the amount of times I've bled, even using VCDS.

Anyway... I couldn't get the Output Test function in VCDS to operate the ABS/ESP solenoids, the only way I could see of clearing any sticky valves.

With confirmation from RossTech too, this control module does not support output tests.

I have contacted BBA Reman and ECU Testing, anyone know any others? Or has anyone tested the block themselves?

[allan_audi]

Hmmm, no replies.

I decided to go ahead and dismantle the ABS block and do some of my own testing. I removed the four screws holding the plastic cover on the block and you can see the 12 valves and coils. Nothing more to be seen really....

I printed out the circuit diagram and did some checks on the coils. All the coils seem ok, plus they seem to operate fine when 12 volts is applied.

Trouble is now all the electrical side is fine, I'm thinking is there something wrong with the hydraulic side, a ball valve or valve seat stuck or worn.

The only thing I can think of doing is to make up a test box and operate the pump and valves when installed on the car, ie. manually work the ABS block disconnected from its normal controller.

Does anyone have anymore ideas? I'm not sure how far these testing companies go, do they check hydraulic operation?

[allan_audi]

I have finally confirmed my ABS block to be faulty. Looks like one or more of the valves are leaking in the seconday circuit causing that circuit to lag. Electrically the unit is ok, all the valves operate so thats why there are no lamps or fault codes. I've also confirmed that the new master cylinder is ok, plus dismantling the old one has shown no problems with that either.

Does anybody have a spare ABS block or know where I can get hold of one?

8E0614111T or 0265202401

I've seen a few on ebay but I'm worried they'll be in a similar condition.

[allan_audi]

Still no closer to finding the problem with my brakes....

I have either refurbed or replaced all calipers so they're nice and free, replaced the ABS block and master cylinder, bled the system several times over using the correct procedure, replaced all discs and pads...

But the brakes still don't working correctly, well sometimes they do sometimes they don't...

When they're working you can really feel the brakes working (you get a nice feel), but when not there is always a pull to the left and a dull feeling.

What is weird is that when I've been on a journey the left front and right rear circuit discs always seem warmer than the other circuit.

I'm not sure what else to look for, there doesn't seem any play in the wheel bearings (someone mentioned play can cause lack of feel), but not sure whether play is noticeable with taper bearings?

Does anyone else have any ideas??