# Audi A4 Brake servo problem



## ktbstudio (May 5, 2006)

Hello, i have a friend who owns an Audi A4 make 2002, 1.9 TDI, engine code AVB.
The problem is with the brake servo, sometimes has effect sometimes no. With the engine stopped if i push the pedal sometimes and then i start the engine with the pushed pedal, it pulls the pedal but sometimes when the car is going with 60 km/h there is no brake servo. The pedal is rock hard.
We changed the brake servo, the servo effect is better, but sometimes has no brake servo. I verified the hoses of the servo, when the engine is running on idle, it pulls my finger.
I want to know if the tandem pump is faulty. Can you tell something about this?
Thanks for help.


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## spitpilot (Feb 14, 2000)

*Re: Audi A4 Brake servo problem (ktbstudio)*

There's usually a "one way valve" in the vaccum system to maintain vaccum in the brake servo even after engine dies to give you power braking to stop if engine dies at speed....if dirt gets in this valve or the valve internal parts fail...this can mess with the vaccum getting to your servo...make sure this valve is in proper working order (you can blow thru it from servo side to motor side, but can't blow thru it the other way 'round...and when you do blow from motor side to servo side..there's no leaking of air pressure)....you don't wanna be replacing/rebuilding a vaccum booster pump only to find out it was a $15 valve that was the culprit!


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