Corrado brake bleeding problem

[Trev16v 0]

Hi,

 

On our Corrado 2L 16V, I had to replace a corroded brake pipe that sits on the rear axle driver side (the one that goes along the axle between the two flexible hoses).

 

While I was replacing this pipe, I had a proper brake hose clamp firmly on the first flexible hose. Despite doing this, I went back outside to find that the bugger had still dumped lots of fluid onto the floor. The brake reservoir tank had run empty, probably below minimum.

 

When I came to bleed the brakes, we were initially able to get some fluid out of the caliper, but then it stopped. Even with the nipple fully open, nothing would come out and the pedal remains rigid. I most definitely do have the rear brake regulator held open. I have even disconnected the brake pipe from the regulator to see if any fluid comes out of there, to rule out a problem with the regulator or blockage in the pipe that goes from the regulator to the caliper via my new pipe. Even with the pipe disconnected at the regulator, I still can't push any fluid out.

 

If we apply pressure and undo the nipple on the caliper on the passenger side (opposite to the side I fitted the new pipe to) fluid will freely rush out.

 

I believe that the ABS system on this car is the Teves 04 or something. When the ignition is turned on and car started, the ABS light goes on for a few seconds and then turns off just like it should.

 

Is it possible that the ABS unit has completely shut off the supply to that pipe?

 

Other thing I have just noticed (and adding to this post afterwards) is that even though the reservoir looks fully topped up now when looking from the top, the fluid doesn't appear to be anywhere near the minimum mark on the side. It could be because it's an old and discoloured tank, but it actually looks like the back part of the tank is right to the top (I think there's a separate section inside it) but the front part seems to sit well below minimum. But the fluid in the top is literally just a few mm down from the top.

 

We ensured that the pedal was not pushed too far (I know it should not be pushed to the floor, so that seals aren't damaged) and once the problem is rectified I shall use an Easy Bleed which I've just found.

 

Desperate for help here as this is an apparently simple job gone bad. Car needed for tomorrow.

 

Thanks

 

Trev

[Trev16v 0]

On further inspection, the reservoir really is above the minimum mark. I just could not see due to discoloured plastic. So please ignore that one.

[ANDREW 30 0]

I'm sure i've read on here that the ABS unit has bleed nipples, so it can be bleed too!

[Topaz2008 0]

I think the bentley manual states that when bleeding the rear brakes turn on the ignition, open the bleed nipple and press the brake pedal. The ABS pump should cut in and pump the fluid through.

 

:D :D

[Gareth_16V 0]

I've just had this with mine. The teves 04 ABS does not have bleed nipples on it. I found that I had no fluid to the right rear caliper, I undid the brake line from the ABS pump itself and could not get any fluid to flow out. I checked the brake line was free by blowing down the line with a piece of rubber fuel hose, with the bleed nipple open on the caliper - it was free.

 

With this problem, the ABS light will not come on, as this is not an electrical problem, it's a mechanical problem that the ABS system cannot "see" by having an electrical signal/voltage out of spec and raise an error code.

 

I think your best option is a second-hand ABS pump (try the For Sale section on here, there's a few people breaking 2.0 16V'ers). It's not hard to change on one of these, but you will need to make sure that the system is fully bled afterwards. It's good because it changes the brake fluid.

 

Before undoing any of the connections, plug the small connector for the "new" ABS pump in, and turn the ignition on. The ABS light should go out as normal. If not, don't waste your time to fit the new pump, as it is more than likely faulty.

 

Hope that helps, good luck with the brakes.

 

Gareth

[Trev16v 0]

Hello Gareth,

 

Many thanks, that's very interesting. Yes, it certainly seems that it's a problem that the self-diagnostics cannot 'see', as you say. When the diagnostics check the operation of the solenoids, for instance, I expect that all it does it check that the solenoid coils are present (and non open-circuit) by measuring current flow into them. But if a solenoid has become mechanically stuck, presumably it would have no way to determine this.

 

What really pains me in all of this is that the ABS was working absolutely fine until I let the fluid drain out. I can't understand how I could have damaged it so easily.

 

Fortunately I do have the spare ABS unit from the wife's old Corrado which is exactly the same unit, and that was working fine. So I do have another one I can fit. But, before I go ahead, how can I be totally, 100% sure that I really do have a fault with the unit? It's a lot of effort to go through if it turns out there's some other stupid thing I have overlooked. And secondly, how on earth do I avoid doing such damage to the replacement unit? I am guessing that I should just ensure I pressure bleed fluid through the unit before ever turning on the ignition, and never power it up 'dry'.

 

Many thanks for your help, it's much appreciated. I could in theory brave the rain and replace that unit this afternoon, but I need a sort of final push to convince me I'm doing the right thing!

 

Is it a fairly common fault symptom for a valve to stick?

 

On a final note, I did just go out to try the method of holding the pedal while turning on the ignition. I had the nipple open. When turning on the ignition, the ABS did its usual self-check and the light went on for just a couple of seconds. But I could not hear the pump continue to run, and nothing came out of that nipple.

 

Trev

[Trev16v 0]

Okay, this afternoon I went ahead and fitted the ABS unit from the wife's previous Corrado, which was exactly the same car and had an equally low mileage (about 70K) and was broken up after it was rear-ended. I'm extremely glad I kept all of the mechanical and electrical parts off it.

 

After fitting the 'new' ABS unit, I fitted the pressure bleeder and I had new fluid flowing out of all four corners without any problem at all.

 

The only issue I have now is that the pedal pretty much wants to sink to the floor. I think that I must still have air in there somewhere, even though I shoved lots of new fluid through. Any tips on this please? It's now too dark for me to continue working on it and I shall have to resume at the weekend. It's far too bad at the moment for the car to be driven.

 

I hope that the old ABS unit really was definitely faulty after all that effort! What does bug me a bit is that I never tried the pressure bleeder with the old ABS unit. I only tried the pedal method. In fact, I even drove the car around gently outside the house with the nipple completely undone on that caliper, and still no fluid ever came out. And when I did move it around with that nipple undone, I had a very firm brake pedal. In fact it felt too firm. I hope all of this confirms that the valve must have been stuck in the old unit.

[Supercharged 2]

Hi Trev, did you bleed the master cylinder? If this doesn't sort it then the MC might be at fault - seals damaged...

[mattwelcer 0]

Is this the ABS system that has to be bled using VAG-COM? i.e at the ABS brake pump

 

http://www.ross-tech.com/vag-com/cars/absbleeding.html