Gas Gauge Thread

[Kpar]

Can somebody tell me what the thread is on the brass hex tube at the back of the fuel gauge. I purchased a gas gauge line kit but the nuts supplied seem to have a different thread. Also is there different sizes for the copper tubing ?. The one on my 33 is 1/8" OD, the kit I bought is a lot smaller.

[Brian]

5/16"x28 TPI

[koates]

Hi there. If the OD of your fuel gauge capillary copper tube is 1/8" (.125") then it is too large and not correct for the application. My original 1934 ford fuel gauge air line is .099" OD. The replacement reproduction copper air lines are approx. .085" OD. You should be using that one. So Im not sure what size air line nut you are trying to fit onto the gauge unit male thread. The air line kit fittings should fit correctly. The original air line tubing was permanently attached (soldered or braised) to the fuel line and supplied as a single part. This air line tube has to be absolutely air tight from the gauge to the tank sender to work correctly and therefore all your line fittings must fit perfectly. No rough jobs, incorrect fittings or sealing tape etc allowed here. Regards. Kevin.

[Terry,OH]

When the nut is tightened down on the fitting it seems to distort the first few threads on the hex tube. Makes them bulge slightly, you can usually get the new nut to start, by hand.

[G.M.]

Originally Posted by koates

Hi there. If the OD of your fuel gauge capillary copper tube is 1/8" (.125") then it is too large and not correct for the application. My original 1934 ford fuel gauge air line is .099" OD. The replacement reproduction copper air lines are approx. .085" OD. You should be using that one. So Im not sure what size air line nut you are trying to fit onto the gauge unit male thread. The air line kit fittings should fit correctly. The original air line tubing was permanently attached (soldered or braised) to the fuel line and supplied as a single part. This air line tube has to be absolutely air tight from the gauge to the tank sender to work correctly and therefore all your line fittings must fit perfectly. No rough jobs, incorrect fittings or sealing tape etc allowed here. Regards. Kevin.

The OD of the tube is not important, the ID is. G.M.

[B-O-B]

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You might want to be careful on tightening the nuts on those old brass fittings as they can be brittle & snap pretty easily.

[Kpar]

Originally Posted by Brian

5/16"x28 TPI

Thanks Brian, I did use a thread gauge to check but I think it has been stressed by over tightening in the past.
Also thanks to all other responses on correct sizes.

[deuce_roadster]

The correct small air lines I have seen have very small tapered ends that you need to solder on AFTER slipping the nut over the end of the line.

[morrisgauge]

On the hydrostatic gauges, we find it beneficial to service the gauge and follow the calibration procedure outlined here:

[wingerdinger]

Thank you, Morrisgauge, for the document. I have been looking for something like that for a while.
My tank unit is in fair condition after soaking and cleaning, except that the air chamber is full of holes. I am going to attempt to solder or braze it.