Weird brake problem

[Error404]

I started my CQ today after replacing a load of parts..

I've got really low pressure, i can push the pedal to the floor and the pedal feels a little like its being modulated, as if the ABS pump is working I pulled the ABS relay and it carried on. The brake performance is shocking as you'd imagine, the pedal feels like a sponge, the car does not stop!

BUT.. when the engine is off the pedal is very firm - i replaced the rear calipers and brake lines and flushed the system with 1.5 litres of fluid. I've tried bleeding them again but no bubbles or fizz came out

I've checked the Pentosin level which is fine... can't think what else it could be!

Any ideas?

[LHD_Kid]

That is your bomb or the servo ........
check you have no fluid leaks, and also that the servo does not leak pressure internally.....
If you leave the engine running for a while does it still do it?
Also, check the fluid levels....especially the power steering fluid level...
Chris

[Cullam3n]

I just had a problem similar to this. Replaced the bomb, hydraulic pump, master cylinder, rear calipers.

Servo was bad.

[Error404]

Cheers guys

i thought it might be, but the bomb is dead in my other coupe and I don't get this kind of problem.. level are all definately up to the max, that was the first thing i checked..

I think the master clyinder might have seen better days, the pedal took a while to recover when i was bleeding the brakes....

Where is the Servo and how do i test / replace it?

[Cullam3n]

I think the master clyinder might have seen better days, the pedal took a while to recover when i was bleeding the brakes....

Where is the Servo and how do i test / replace it?

The servo is right behind the master cylinder. The master cylinder is fairly easy, just messy to be honest. AFAIK it's the same on the v6, all it is, is 3 metal pipes and the resovoir. Two bolts hold it in to the servo, the resovoir just pulls out as it sits in rubber grommet-type things.

[Error404]

so i pull the reservoir off, undo the brake pipes off the master clyinder and remove that - how does the servo come out and how much to replace it mate?

[shark_90]

That sounds exactly like my problem on the S2. Another bill!

[Cullam3n]

so i pull the reservoir off, undo the brake pipes off the master clyinder and remove that - how does the servo come out and how much to replace it mate?

What I did was I just removed all two or three lines that connected into the master cylinder. I had a towel underneath all of it to catch the drippings. Then there's a bolt on each side of the cylinder that goes into the servo. You undo those, and then pull the cylinder straight out. You'll see a thin metal pipe that pushes into the master cylinder from the servo, pull the cylinder until you are clear from that pipe.

Once the cylinder is removed, I just carefully manuevered it to a tray and then turned it upside down to drain the brake fluid from the resovoir (from the cap). Then, you just take hold of the plastic resovoir and firmly wiggle side to side, and it should put out. Not straight up if I recall correctly, kinda off to the side like you are prying it off. You might pull the black grommets out with it, might not. They just pop in and out anyway. I also gave a good clean with a degreaser I had.

Also there is a rubber pipe that goes to the resovoir as well, disconnect that (it just pulls off, the plastic bit the rubber hose goes on to is barbed)

The garage did the servo for me as I didn't know what it was at the time. So I haven't done it but it looks more the same except that the servo is bolted to the firewall and you need to get underneath the dash above the brake pedal to get to the head of the bolts. It also has two? hydraulic lines. I believe the hydraulic system is self bleeding afterwards so I wouldn't worry about the leakage. Other than that, I can't really tell you because I haven't done it. I bought a 2nd servo from audibits for 35quid, but a brand new one will cost you

HTH

[Error404]

hmmm. seems thats what i'll ahve to do - yes just looked at some diagrams, i think once the master cylinder is off i just need to reomve the fluid lines and unbolt 4 bolts from the drivers footwell to get the servo out..

I've got a replacement bomb coming so i think i'll do both at once... more on the list to do!!! Seems never ending at the moment

[LHD_Kid]

The servo is huge money from Audi, VAGparts or Quattrocorner would be cheaper...
However... its worth checking this first, you can test it to see if it is loosing pressure, by removing the return pipe from the servo to the reservoir, if more than 1 or 2 drops of fluid come out it will be the servo...(This is how you do the S", expect its the same for CQ)
BUT, it is possible to replace the o rings inside the servo, I will be doing mine with my trusty Romanian mechanic friend (thanks Eugen ) as I am suffering similar troubles...
I don't know what the differences are between S2 and CQ in this regard, but this would easily be the cheapest route, especially if you can't find a known good one...
HTH
Chris
(I will be poosting pictures on doing this, as I reckon it will be very useful to the rest of the Audi community, but not starting it until next weekend...!)

[Cullam3n]

Yes I forgot to mention there is a seal kit you can get for the servo, remember reading a guide somewhere. Actually, I think it was for the hydraulic pump.

[Error404]

sounds good chris, i'll try the test with the return hose - should the engine be running?
Is there a rebuild kit for the servo then? Or are you finding seal etc of the right size to use?

I'll have a scout about see if i can find out how much a new one is.... bloody expensive i'll bet!

[LHD_Kid]

Audi do not list a kit for repairing the servo.... you need to source the correct size o-rings, which is not hard, but you need to split the servo to see what is needed, maybe it is the same as the S2 ones, which I will know the size for in a week or so....
Audi will not have these sizes written anywhere either, don't know why, other than meaning ordinarily 500 quid or something for a new servo.....
definately worth a shout if you can't find a pre-owned beauty....

[Cullam3n]

sounds good chris, i'll try the test with the return hose - should the engine be running?
Is there a rebuild kit for the servo then? Or are you finding seal etc of the right size to use?

I'll have a scout about see if i can find out how much a new one is.... bloody expensive i'll bet!

hold the engine at 2k rpms for a bit, and then disconnect the return line of the servo and look for any drips.

[Error404]

ah! spotted your other post now Chris

Thansk Cullam3n