Vacuum tanks.

I note the comments re fitting electric fuel pumps to replace the vacuum

tanks. This is like hiring a bulldozer to crush a butterfly, as the

vacuum tank is the most reliable unit you can ever have. In 45 years

motoring, (400,000 miles) in my '28 Essex, and almost 30 years in my '29

H 7 pass, the vacuum tanks have only played up once on each car. In

the Essex, the float developed a leak, the tank filled right up, and

sucked fuel through the vacuum line. Easily fixed, and this 30 years

ago. In the Hudson the flapper valve assembly unscrewed and dropped

into the bottom of the tank. Up to '27 the tanks had cast pot-metal tops

with a toggle lever which flipped the valve by a brass spring as the

float rose. The pivot points can wear, sometimes delaying the action,

but the most common problem with these tanks is the brass valve seat

popping out of the top. If this happens, re-insert, and carefully pin

punch around it to hold it in. '29 thru '31 models had leverless

tanks, and there were three variations of this. The first in '28 used

a goosenecked float wire to actuate the valves, and the wires from the

valves had little circles in them. The second had a slot in a flat

strip on the float, and the valve wires had right angles in them, and

there is vary small compression which must go underneath the valve

wires. I'm not familiar with the constant suction type, but in '30

there was a "vacuum booster" used. This is a small venturi venting to

the atmosphere directly behind the vacuum line, and the wiper connection

goes out the top. The idea of this is that there is a constant stream

of air going past the top of the tank, and this produces the difference

in pressure to induce vacuum in the tank, rather than engine vacuum

alone. This eliminates the rolling due to enrichment of mixture as the

top chamber fills, as on earlier models. In all models, the most

important thing is to have a good top gasket, and thin rubberised cork

is the best for this. Also, some models have pot-metal flapper

valves, and these tend to swell and crack. I usually turn the fibre

flap around to give a new surface, and carefully sand off the face of

the pot-metal body to give a flat surface. '29 thru '31 models had the

filter bowl on the bottom, and these are supposed to shut off the fuel

flow when you undo it, but this seldom happens, as the cork seat gets

distorted, so have a container handy to catch the fuel if you undo


Geoff Clark.
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