Hi Gurus,

I have a Q7 2007 3.0TDI UK import in New Zealand. My car brake padle sinks to the floor after driving around 120km. Happened twice, If i keep driving another 200km the brake doesn't workand Paddle goes all the way to floor.

Took it to mechanic , No Oil leak, Master cylinder replaced with second hand one, Brake servo tested and OK. No hot disc after padle sink , Brake pad are in good condition, Can't see any piston seize from outside. what the hack ...

I have only noticed the rear discs are bit low and may need replacement but that shouldn't let Brake padle to sink to the floor after 2 hour drive ?

Paddle comes back to normal after normal bleeding procedure and stay fine if I drive this car locally or don't go too far more than 100km.

Can someone please help !

Regards,
Ankit
AnkitSaini is online now Report Post

 

There has to be a small leak somewhere. Air is being introduced into the system somewhere. It doesn't take much air to cause and issue like that. I'd inspect the flexible rubber lines that connect the calipers to the hard lines. Always go with new/rebuilt master cylinder and caliper parts. The thing about brake fluid is that it hydroscopic and will attract moisture even under normal operating conditions. Moisture leads to corrosion inside the system. Corrosion makes tiny particles that will scratch and tear the rubber seals in the master cylinder causing leaks. If a used master cylinder is removed and sits on a shelf for really any length of time, moisture will start to accumulate in it. This will quickly lead to the same issues.

 

Hi Dave,

Thanks for your advise, I will take my car to the mechanic tomorrow and check the flexible rubber lines that connect the calipers to the hardlines. If everything is fine there , i will be thinking putting the rebuilt master cylinder.

I will keep you updated..

Regards,