Fuel Tank replacement

Hello

I am in the process of replacing the fuel tank on my '74 6-cyl S3 109 (the old one was leaking and full of sand...). The replacement part has arrived but it turns out I did not get the exact same model as was installed previously (stupid mistake; I was confused some of the indications online and did not compare sufficiently carefully) - the difference being the number of pipes sticking out. My old one has four pipes on top (plus the hole for the sender unit), the new one only has three. It seems that the dimensions of the two tanks are the same, so fitting the new one should be possible.
My question is about the connectivity, however. On the old one I have one venting pipe (connecting to the filler), one pipe connecting to the pump, and one that connects the two "sections" of the tank, to prevent one side to be at under-pressurised. How is this done when there are only three connections, what are the three for?

For completeness, here are the two models in question:
My old tank is like this one: https://www.famousfour.co.uk/new_parts/ff_part?part=18412
The new one is this one: https://www.johncraddockltd.co.uk/s...m/599233-fuel-tank-petrol-rear-1975-1984.html

Cheers,
Andreas

Just done this on mine....so one pipe for breather to the filler neck, two remaining pipes to each other for balance, then the sender has an output for fuel pickup to the lift pump. You might need to change to a latter sender that has the integrated output.

Thanks. I guess you are right and I need to replace the sender - am I correct in assuming that the fuel level indicator in the dash does not care what sender is attached?

Could you put a tee in the line joining the two halves and link that to the filler?

rob1miles said:

Could you put a tee in the line joining the two halves and link that to the filler?

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The problem is that the missing connection is to the fuel pickup - otherwise it would indeed be an elegant solution.

The tank is now installed, and I am waiting for the new sender/pickup... For now I just have the old pipe stuck through the rubber piece that was sealing the hole for the sender unit. I dont think I can drive well with that, but at least I can purge the entire fuel system now (had water in the tank, and thus everywhere including the carb). It turns out the dimensions of the tank are also not exactly the same as the old one, so it was a bit of a hack to get it fitted - but I am actually not really sure I understand how the size could change, given that the chassis for all series 3 LWB is the same (right?). Maybe it is just a cheap tank...

My replacement tank took a bit of persuasion to get in so think they just are not a great pattern part......beats petrol spraying everywhere though! New sender should come with seal but might not come with the fixing for the sender....worth checking as its an interference fit not screw in like your old one.

Mingus said:

My replacement tank took a bit of persuasion to get in so think they just are not a great pattern part......beats petrol spraying everywhere though! New sender should come with seal but might not come with the fixing for the sender....worth checking as its an interference fit not screw in like your old one.

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A good pair of spanners is very convincing
My problem was more the water getting in than the gas leaking out. I actually think the tank might still be fixable, but there was so much crap inside that I decided to just part with it for good. If anyone is interested, he/she is welcome to pick it up (Switzerland...).
I ordered everything needed to install the new sender (fingers crossed), but it may take a while, so I will try to run with just the pipe sticking into the tank.

Can you put a 5/16 bulkhead tube fitting through the sender and fix a pipe through?
https://www.wadefittings.com/resources/Wade_Compression_Fittings.pdf

rob1miles said:

Can you put a 5/16 bulkhead tube fitting through the sender and fix a pipe through?
https://www.wadefittings.com/resources/Wade_Compression_Fittings.pdf

Click to expand...

I suppose I could do something like that - but since my old sender unit is one that is fixed with 6 screws (rather than a clamp ring) it would not be a long-term solution either. New unit has been ordered, so I just need to be patient and drive without knowing the fuel level in the tank