I have a 2003 Allroad that has just started this recurring problem after the car has been parked for several hours. Upon start up, there is no brake pressure! It takes a lot of pumping to get to the point where the car will actually stop. It happens if the car is garaged, and when it is not. I live in Canada and have owned the car since Sept and this problem started 2 weeks ago in mid January. Brake fluid levels are OK and brakes seem to work fine once you get going. Any ideas on what is causing this very frustrating, annoying and dangerous (!) behaviour ?

 

the power brakes are vacuum assisted so if you have some kind of vacuum leak than that could cause it, but its really strange that it would go away after a short time. are your turbochargers still working properly?

 

There should be a check valve in the vacuum line that leads to the booster. It prevents the vacuum that has accummulated in the booster from leaking out over time. This provides full braking power upon startup.

If that check valve gets a bit of crud in it, it can allow the vacuum to release over time. Then, when you start the car, it has to build that vacuum back up again before you have full brakes.

If the check valve "checks out", then move on to searching for leaks in the line, or a torn bladder in the booster itself.

Good luck.


P.S. This information is based on "general automotive experience" and not necessarily specific to the allroad. However, I have peeked under the hood on a few occassions, and everything relating to the brake booster appears to be standard parts.

.