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hi there guys,i have my car driving ok and when braking i was getting a vacuum noise coming from under the car,found the issue it was the brake vacuum valve ,i took it apart before and there is a cardboard diaphragm inside which is very hard,i have replaced this with neoprene rubber end of noise,my question is upon braking i get a slight misfire /shudder from the engine for a few seconds then disappears until braking again,this is sucking in air via the diaphragm to atmosphere thus making it miss etc,to me this looks like the design of the system, is this correct
cheers Dave

It's entirely normal on the B-K equipped cars with mechanical brakes to get an ever-so-slight change in idle as you initially step on the pedal and the system draws vacuum. It's nearly imperceptible and if you have any more than that you probably have a vacuum leak somewhere info the system, either a hose connection or more likely, a worn piston or shaft seal in the power cylinder. Parts all available from C&E.

Put a vacuum gauge on the system and watch the action of the gauge as you step on the pedal - you should get a slight drop in vacuum as you initiate braking and them, with the brakes still applied, it should return to normal. If it does not return to normal, that would confirm a vacuum leak.

hi cheers for reply it was my thoughts as the design of the valve to atmosphere,the valve gives the manifold a temporary air leak by design, i just wanted to check to see if i was missing something cheers Dave