Simple question i think,, on a 1991 300d 2.5 to test the vacuum pump in the engine, the book if i read it correctly says to disconnect the vacuum line going to the brake booster, ( line B). Then check the restriction orifice at the ancillary connection. It then says to hook up vacuum meter up to the ancillary connection. Is this done with the break booster line still disconnected? wouldn't you just pull in atmosphere?

I though the best way to test was to cut into the system with a t connector and then measure the whole system,, not just the pump, let me know,,please[8D]

 

I think there is a one-way check valve in the booster hose so once disconnected, the hose cant loose vacuum.

 

Benz Bob, i thought that too, but then why remove the hose? if it has a check valve in it,, it only goes one way. If the check valve is to swing closed towards the booster,that means that when the vacuum pump is on it would keep the check valve open. If the check vlave is to swing closed to the vacuum pump that means when the pump is in service, the booster gets no vaccuum,,, either way which way do you test your car?? with the hose off or on??
[8D]