poor braking on acceleration

[2dogsjohn]

if i accelerate hard and imediately hit the brakes they are "kak" to put it mildly ,there is an initial braking which quickly fades to practically zero.the car has stock setup but all brand new.however i dont feel the problem is the brakes themselves. is there a vacuum pump fitted to the servo on RS4s;i ask this because i have wondered if during accelleration the pressure in the manifold causes the lack of vacuum in the servo (normally created when you lift off) hence the servo is not fully evacuated if you like.i know some cars are fitted with a vacuum pump for this reason.the syptoms are exactly like braking and then turning the engine off.under any other conditions the brakes seem fine. ANY IDEAS

[jimbo1234567]

sounds like the non return valve on the pipe going to the servo is defective. try taking it for a run then let off for a few seconds before hitting the brakes, this will build up a vacuum in the servo and the brakes will work properly, if it works then the valve is faulty. the vacuum line plugs into a rubber grommet in the middel of the bulkhead behind the engine

[kookieS4]

....I had a mouse gnaw its way through mine...!!!!

[2dogsjohn]

without even trying it i know this is the case;the brakes work fine as long as theres a pause betweeen flooring it and braking.any idea how complicated to change and how much they are.thanks

[2dogsjohn]

is the non return valve in the grommet