All brake servos have a one way valve and its usually on the end of the pipe you actually push into the servo ... no check valve and on over run you would have no vacuum in the servo
The Tandem pump replacement itself is not hard .. but if the bolts have seized they will just round out ( Torx ) .
In this case you have to remove the bumper and possibly the exhaust that's in front of it then being a bit brave start attacking around the bolts with a hammer and chisel to snap away the casing or try and drill them out .
i've used the hammer method a few times and its quite effective shall we say .
The Tandem pump replacement itself is not hard .. but if the bolts have seized they will just round out ( Torx ) .
In this case you have to remove the bumper and possibly the exhaust that's in front of it then being a bit brave start attacking around the bolts with a hammer and chisel to snap away the casing or try and drill them out .
i've used the hammer method a few times and its quite effective shall we say .