MB Booster problem. Sprinter 2006

Brand: Mercedes Benz
Model: Sprinter
Year: 2006
kilometers: 999
SCOPE: 6
Power (CV): 125
Fuel: Gas
Type of injection: Carburado
Marcha change rate: STD
Modifications of the car: Motor Change Gas Disel

I have a problem with this booster, they disarmed it to give it service and not stay. First I was very hard for what I assumed that the booster was unused and then disarms it and accommodates a couple of joints that seem to be badly put and started working but now the problem is that after several bombings to the pedal the truck is braking as if you were stepping on the brake ..... already check it several times and everything is fine apparently already changed the vacuum valve.
The part number is: a001 430 00 08 Q5 Trw
any contribution will be well received, thanks