When I took the brake booster pipe off after the car had sat overnight there was a hiss of air which I think says the booster is not leaking. I have now taken the pump off again, cleaned it and checked the primary (Brake boost) and secondary (engine mount) one way valves on the pump. The brake one was open but started to work after I cleaned it using carb cleaner, the secondary was ok. The vane inside the pump was ok and moved correctly. It is difficult to see what could go wrong as it is so simple but when I re-assembled it and tested the secondary take off I was still only getting 10 inHg. If I revved the engine it went up to 15 inHg but I then noticed oil in the test vacuum pipe. Also if I released the vacuum it didn't get above 2 inHg at idle unless I revved it again when it went back to 15 inHg.
I was testing at the connections to the pump so as to take the pipes out of the equation. For completeness I put 25 inHg on the secondary take off pipe and it held fine. I also check the front engine mount and that was ok. I then put 20 in/Hg on the pipe from the vacuum pump to the brake servo and that held ok. I did however note that there was oil on the inside wall of the pipe.
A test drive confirmed unsurprisingly that nothing had changed.
My conclusion from this is that the pump is broken in some way (valves faulty, vane excessively worn after 225k miles) and the only solution is a new pump but I am far from convinced on my hypothesis.
Does anybody have any suggestions, advice or guidance before I buy a new pump. Thanks
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