The 2CV workshop manuals provide “manufacturing drawings for tools not on sale”. One of these is the manometer used to measure the crankcase vacuum.
Usage instructions are quite simple:
To check the vacuum in the crank case, use a water manometer RM. 630-56/9a/
One of the ends will be connected to the rubber guide tube for the oil level dipstick.
While engine is idling, accelerate slightly to stabilize the manometer levels.
The liquid should climb in the section of the manometer connected to the engine.
Read the difference in levels :
It should be :
– with engine idling : 5cm (1.96 in) of water min.
Otherwise, the breather must be replaced.
The vacuum should never fall to zero, no matter the engine speed.
The images are taken from the Citroën Repair Manual No. MAN 8161, Volume 1, October 1983.