Ur quattro rr

[steverrquattro]

Hi,

It is item 4. Periodically and over time the pressure escapes from the pressure accumulator. Also named the 'Brake Bomb' because of how it looks.

The normal way to test this is after turning the engine off. See how many brake depressions you can get before the pedal goes hard. The less the number of depressions = knackered pressure accumulator.

The job is relatively straight forward, BUT remember to do around 20 depressions before disconnecting the high pressure brake line. The brake pipe union can be a little fiddly so take care not to cross thread this. Oh and get ready to get fluid all over you. :-)

Just thought of this, there are washers on the banjo fitting, so don't loose them and remember to top of the fluid which you will loose.

[predding]

I'm happy to report that it was the brake accumulator. It must have been completely knackered as you didn't even get one pedal depression out of it!

No more warning light when the pedal is depressed, no pulsating feeling and lots of depressions of the pedal after the engine has been switched off.

Hi Steve,

I have a similar situation with my RR 20v. After 12kms of driving the brakes start binding. There is now a fluid/hissing sound coming from the brake servo area. I have removed the master cylinder and prop valve and all is good and no leaks. On return from the drive, the hissing came on by itself for 4-5 secs and the brakes bound even more. I am tring to identify if this is the Brake servo or the accumulator.

I have depressed the pedal with he engine off, it went to the floor but the next push was hard and that was it ie no further depression
I have looked for the accumulator but cant see it, ca you guide me ie is it under the abs unit and what do you have to remove to get to it
Is there a way to idntify which one has failed ie the servo or the accumulator as there is a rebuild option for the servo as you have now mentioned.

Thanks for any info

Here is a link o the system diagram http://www.oemepc.com/audi/part_sing...4/lang/e#sec_7

[newsh]

Good news Steve!

[steverrquattro]

I'm happy to report that it was the brake accumulator. It must have been completely knackered as you didn't even get one pedal depression out of it!

No more warning light when the pedal is depressed, no pulsating feeling and lots of depressions of the pedal after the engine has been switched off.

[carr2112]

rear calipers

Take off rear calipers and Try inverting the rear calipers when bleeding, had the same problem. Will take a few attempts i found.

[steverrquattro]

I've removed the return pipe from the Brake Servo and there were lots of droplets of PAS fluid. So much so, that after 1 minute, it was still gushing out so I just refitted the union.

Putting on a brave face, I have contacted GSF who told me it is not available. Not to worry I thought to myself as Pete reeve will have one of these and guess what........he hasn't, nor has he ever supplied one.

I talked to him about all the threads on here and that people had replaced them, so my question is, where do I get one from?

Is there a seal kit available?

Is this the correct part number 857612107C ?

I think I've done this wrong. Having just repeated it now and for clarity, no droplets came out of the Brake Servo and the fluid just stayed level at the top of the hole from where I took the return pipe out.

However, it was the return pipe from which the droplets came and NOT the Brake Servo.

Can I assume that with a faulty Brake Servo, you are looking for any PAS fluid to come from the hole where the return pipe fits in the Brake Master cylinder?

[Pete Reeve]

Hi steve the correct part number is 859 612 107 for the RR quattro

[steverrquattro]

I've removed the return pipe from the Brake Servo and there were lots of droplets of PAS fluid. So much so, that after 1 minute, it was still gushing out so I just refitted the union.

Putting on a brave face, I have contacted GSF who told me it is not available. Not to worry I thought to myself as Pete reeve will have one of these and guess what........he hasn't, nor has he ever supplied one.

I talked to him about all the threads on here and that people had replaced them, so my question is, where do I get one from?

Is there a seal kit available?

Is this the correct part number 857612107C ?

[steverrquattro]

Not trying to be cheeky but did you bleed both sides on the big reds... If you only
did the outer you would get pretty harsh vibration...

cheers, Mike

Yes I did.

I'm going to remove the return hose from the Brake Servo today as this seems to be the best way of checking. If little or no fluid comes out, then it should mean that it is the Brake Accumulator.

Got this from S2central's site:

Testing the brake servo for leaks -

Keeping the engine off, disconnect the hydraulic RETURN pipe on the brake servo. A few drops of hydraulic fluid should escape. If a continuous flow is observed, the brake servo is faulty and must be renewed and reconnected to the hydraulic system.

http://s2central.net/main_frame.html

[audiurq]

Not trying to be cheeky but did you bleed both sides on the big reds... If you only
did the outer you would get pretty harsh vibration...

cheers, Mike

[AndyP]

How can you reliably test the Brake Servo?

The favorite at the moment seems to be the Brake Accumulator, but before I go for it I want to check the Brake Servo.

I have the accumulator off my 3B if you want to borrow it for testing?

[steverrquattro]

I'm afraid this may be the Servo going bad Steve

How can you reliably test the Brake Servo?

The favorite at the moment seems to be the Brake Accumulator, but before I go for it I want to check the Brake Servo.

[steverrquattro]

If the problem was ABS related, try driving with Difflocks engaged- this switches ABS off (Unless yours has ABS switch on dashboard, from memory it was by drivers' left knee on mine,in which case try that).

I've just remembered as well that I changed the Brake Master Cylinder because of probs with mine- not a difficult or expensive job. The BMC came from Pete Reeve, and it arrived the following day.

Just changed the BMC as the front brakes were binding on, hence the brake bleeding.

Going to have another go tomorrow with the foot pedal.

[Tonybolony]

If the problem was ABS related, try driving with Difflocks engaged- this switches ABS off (Unless yours has ABS switch on dashboard, from memory it was by drivers' left knee on mine,in which case try that).

I've just remembered as well that I changed the Brake Master Cylinder because of probs with mine- not a difficult or expensive job. The BMC came from Pete Reeve, and it arrived the following day.

[newsh]

I'm afraid this may be the Servo going bad Steve