Brake Failure!! Hard pedal - What do?

[Doney]

***EDIT: Have solved the problem, see post below***

Hi all, my first post and it's a fairly important one! Just picked up a beautiful 2nd hand 2001 1.9TDI 130BHP with 165k on the clock. I test drove it yesterday and it seemed ok. However, on the way home this evening it had a pretty major brake problem which -worryingly- seems quite common. Here's what I've researched so far:

Problem:
Very hard brake pedal with minimal braking power. I had to STAND on the brakes to bring the car to a stop... needless to say I was ultra careful on my way home!

Known causes (that I have managed to find so far):
1) Water lodging in plenum chamber due to blocked drains either a) rusts, or b) seeps into the servo, taking up space that should be occupied by a vacuum.
2) Weak/thin vacuum hoses collapsing under vacuum.
3) A grommet on the bulkhead deforming and crimping the vacuum hose.
4) Backup electrical pump failure.

Solutions:
...?

While there's plenty of suggestions for causes, there's not as much info on the fixes. They seem to range between €750 for a servo/master cylinder replacement to a €10 hose replacement! (incidentally, the servo replacement usually works for a while before the problem returns caused by another of the issues above)

From what I gather this has become a fairly well known issue but are Audi covering repairs? Will Audi Ireland cover the repair cost on my 13y/o car considering its is a fairly f*****g life threatening problem caused by poor design?

Not sure of the best option from here besides inspecting everything with a fine-tooth comb (unfortuantely I'm really tied up with work and it's dark by the time I get home in the evenings)

Would be very interested in hearing about anyone elses experiences but more importantly, the fixes that actually worked?

Thanks all...looking forward to working with ye!

[old guy]

I am not familiar with your particular model but if it has a suction jet pump I would consider replacing it.

[Doney]

Lovely, thanks! I've found this diagram of the vacuum lines, will prob come in handy later!

[old guy]

Check out #19 and make sure yours isn't split. It is a common problem with the 1.8T engine and it causes the same symptoms that your car exhibits.

By the way, that diagram is for a European version of the 1.8T engine.

[CyberPMG]

Also check the check valves... especially #7. As the B6 is getting up there in years, those check valves become brittle and crack. They're very inexpensive parts to replace. It's very likely the check valve, or something else along the vacuum line (includeing the jet suction pump that old guy mentions) that is causing a loss in brake function.

[diagnosticator]

Sounds to me that the brake booster vacuum was suddenly lost. As you have already noted this can happen for several reasons. The most likely reason is when the brake booster housing is perferated with rust due to blocked plenum drains. Everything will be fine, then the perferation from rust makes its way through the booster steel wall and the vacuum inside is suddenly equalized to ambient outside air pressure, thus the loss of power assist from the brake booster.

[gregory.fazekas]

You have a vacuum leak somewhere in the system, one large enough to cause the brake booster to fail. A good way to determine if its the brake booster itself is to put the car on cruise control and try and press the brake, then compare it to when you have no load on the engine. If its SIGNIFICANTLY more difficult to press the petal with load on the engine, its your booster, if not its a vacuum leak

[Doney]

***Problem Solved, brakes now working OK***!

Hi all, it's been a very long time since I initially posted but I've been busy, here's to close up:


The reason the pedal was hard was because there was no vacuum getting to the servo and the culprit was the rubber grommet between the plenum chamber and engine bay - It was collapsing under vacuum. Once I knew where to look it was pretty obvious; start the engine, and watch the crappy piece of rubber get sucked in on itself. I had an urgent journey one day so decided on a temporary fix which was to fit a small 1" copper pipe inside the rubber joint, reconnect the hoses and that worked beautifully (and still does today!) So no more hard pedal. However next problem...

Now I had soft pedal. The brakes felt a bit spongey on the road and the pedal would slowly drop to the floor while the car was running. Eventually another problem came to light... Vibration from the front wheels under braking - Felt like warped discs.


Meanwhile, an inspection under the tandem pump revealed a swolen coolant hose; Diesel was leaking from the bottom of the pump onto the rubber hose which causes it to go soft. The car was always slow to start from cold since this leak allowed air into the fuel line overnight and it needed an extra turn to get going in the morning (with a nice puff of white smoke) so tandem pump replacement was in order.

Got a used pump for €50 on ebay and a new metal gasket for €11, also 9.5mm fuel line to replace the swolen coolant hose while I had the pump out (Hindsight: 8mm would probably fit better) plus a new coolant temperature sensor since I was down there.

Very tricky getting to the 4 allen head bolts on the back of the pump. The lowest is a bitch but patiece got it out. got the new bits all put in and went to start the car and it just WOULD NOT FIRE UP. I spent about 2 hours trying to bleed the return lines and prime the pump but mercifully, EVENTUALLY the airlok cleared and she fired up.

So now braking is much improved and even the vibration is gone, it must have been a dodgey vacuum causing the brakes to shudder. It's still a tad spongy but I think new brake fluid will fix that. That's next weekend's job. Only drove it 10 miles in snow so far, but everything seems fixed!

Thanks for the help!

PS if anyone needs info on changing the tandem pump or coolant hose, feel free to message me now that I know.