Strange brake pedal feel

[dweed145]

Hello all.

I've just purchased a 2007 A4 quattro s-line special edition 2.0T.
I bought it from a used car dealer and test drove it etc before buying.
After driving it for about an hour I realised the brake pedal feel was a bit weird. The brakes work fine, but the pedal range is longer than I would have expected. On top of that, once you have fully applied the brakes, you can continue to push until the pedal ends its travel at the floor. It requires a fair amount of force to do, but nevertheless it is possible.
In my mind it has a partially blown master cylinder seal or a bulging brake hose. It doesn't seem to be leaking brake fluid.

I took it back to the dealer the next day, and **did phone and tell him what I thought was wrong prior to arriving** (important to note if you are the suspicious type).
He talked to me about it, and then pulled a jeep off the forecourt and showed me the same thing happening on that, brakes being applied, before the pedal slowly sinking to the floor. He then sat me in an automatic A3 and i felt the same thing happen.

I left with the car having been confused enough to accept that maybe I was wrong.

But I can't help feeling that maybe he undid a brake bleed nipple on the two cars he showed me.

Here is a video of it:


I'd be interested to hear what you think?
Is that normal but maybe it's also just got worn out pads? Or is that totally not normal!?
If so I want to try to make him either pay for a fix or at least refund me a bit of what I paid to get it fixed.

[Crasher]

Yes this is a common issue and even the source of a few factory information notices. They key test is to find a quiet bit of road with a decent incline and stop the car and hold it on the brake (which you shouldn't as it dazzles people behind) and keep it held just on the edge of where it creeps. If it starts to move and you have to catch up by moving the pedal more than once there is a problem. Master cylinder failure is almost unheard of these days, if there is a problem it is mostly likely a service brake bleed has allowed air into the system and a proper pressure bleed would fix it. One thing though, over the last few decades I have become used to seeing this on Diesels due to their vacuum pumps strong linear action but not on a petrol where the intake system generates its own vacuum (occasionally having an electric booster pump) but the TFSI has an engine driven vacuum pump.

[dweed145]

Thanks Crasher.
So you are saying it's unusual on a petrol?
I have got hold of a copy of vcds, am I right in thinking I need to connect up the laptop and do a brake bleed through that to trigger the abs pump etc?

[Crasher]

The A4 uses a Bosch ABS pump from memory and does not require a Basic Settings bleed. A petrol without a vacuum pump would not tend to do this. One thing we find with the Bosch pump is that after bleeding you have to find somewhere safe to tigger the ABS and this can stop the pedal sinking and we do a pressure bleed again after. Most of the ones we get with this problem is where other garages or owners have let air into the system for one reason or another and we sort it out for them.

[dweed145]

Thanks Crasher.
I just had my local indie do a pressure bleed and the pedal feel is still weird. Seeing as it's raining I can take it out and trigger some abs quite easily. But does it need to be pressure bled again straight after triggering the abs?
Cheers.

[Crasher]

No, triggering the ABS should firm up the pedal. I am wondering if you have a problem, with the vacuum pump, I don't know if your indi knows how to test and perform the basic settings on it. Private Message me your reg so I can check which system you have but it won't be until Monday now.