1958 fuel tank sending unit for A/C cars - question

[chris_58]

Hi everbody,

 

I have a question regarding the fuel tank sending unit for a 1958 Buick with factory A/C. Those cars came equipped with a fuel return line from a metered opening in the fuel filter to avoid vapor lock. While replacing this return line (a rubber fuel line from the engine to the tank) I stumbled across a mystery that I hope someone can explain to me. I attached three pictures in hopes they will help understanding my explanation.

The sending unit has two hose connections - one that is the pick-up that goes to the fuel pump in the engine bay and the return line (capped off with red cap to avoid dirt getting in while I work on it). When I took the old line out, there was a brass hose connection just before the 3rd clamp in a horizontal position (indicated by green box in blue line). Inside the brass fitting was this lose "piston" (shown next to brass connector). There is no stop for this "piston" within the brass fitting but is seems the fuel hose tightens up just enough at each end to contain that "piston" inside the connector. Does anybody know:

 

a) what this is for?

how does the piston stay in place (am I missing parts)?

c) is it needed or can I just connect the return line directly to the sending unit?

 

Also, as you see from the pictures, the sending unit is wet, because the return line is somewhat lose where it goes into the sending unit. Therefore my question: can the sending unit can be replaced without removing the tank or is it better/easier to drop the tank?

 

Thanks,

Chris

[Ttotired]

Never seen such a setup, but its interesting

What the piston does is give a "line" restriction

Normally, when a car has a return line to the tank, it also has a fuel pressure regulator and the return line is basically a dump line for fuel not required.

The normal carburetor fuel system runs at about 5 or so psi, as that tapping would be technically a leak, it would need to have something to block it so the fuel pump could build up its 5 psi. Unless it doesnt make a good seal to whatever it seals on (and I guess it must be the hose or thats the wrong joiner/valve housing) I cant see how it can do much good at all because there is no way it can govern pressure, its can only restrict or block flow. I wonder if that fuel filter actually has a regulator in it, all it would have to be is a ball valve with a spring?

Now, that housing looks like an ordinary joiner to me, and I wonder wether someone has tried to "fix" a fault and thats there attempt at replacing what was actually a fuel pressure regulator using the piston from inside the original regulator

Personally, I probably would ditch the whole set up and go back to a single line

 

 

[JohnD1956]

It may just be the pictures but it looks like either the same sized hose from the filter to the Carb as it is from the filter to the return line or a bigger return line than carb supply line.  I would note that later years, fuel returns were smaller diameter hose.

 

Plus I would note that it's highly unlikely GM would have run a rubber line the length of the vehicle.  And  I recently saw a 62 Electra with factory air and I noted there was no fuel return line on that car.  So I agree with Ttotired, that looks to be some sort of after build effort by a previous owner.

 

If it were mine, I'd try to get that return fuel line down to a 1/4 " size hose, and I'd also try to use as much metal line as possible under the vehicle. And I would leave that piston out till I knew if it was needed.

[Ttotired]

On the fuel line being rubber all the way, that would be correct, or at least the supply line on my 58 is rubber all the way and the chassis clips match it

 

 

[chris_58]

John,

 

Buick advertised the rubber fuel line as "Anti Rust Fuel Line" (see attached Dealer brochure) and was standard on all 1958 models. LikeTtotired stated, the openings and chassis clips all fit a 5/16 fuel hose.

The vent opening in the fuel filer is metered (see second pic of a similar fuel filter off a Cadillac)). It is just a small opening allowing only a little fuel (and vapor lock causing gas bubbles!) to escape through the return line.

 

I assembled the hoses without the brass fitting and the brass piston and so far it seems to work ok.

 

Chris

[JohnD1956]

I love to learn this type of stuff about all our cars.  Thanks for the post Chris.