Needle in a Haystack

[Jack H.]

An educated guess...

'Tanker' cars are pretty darn rare beasties, but I took a look at the N03 option section of the AIM and noticed there's NOTHING diferent about the instrument cluster. The implication is the electrical function of the tank sending unit is identical to what's used on standard tank cars.

Typically, the differences in sending units deal with mechanical aspects (length and position of float swing arm, mounting of filter 'sock', shape of mounting from the sender flange to the potiameter. That said, I see no reason why you can't 'restore' your original sending unit yourself.

You'll find the potentiameter mounted to the main shaft with a crimped cover that houses the pot's wiper arm and joins it to the sending unit's float swing arm. This is typically where failure occurs.

Either the wire winding in the pot failes by open circuiting or the pot's wiper arm breaks and failes to make contact with the resistance windings. Good used donor parts for the inside 'guts' of the potentiameter ought to be available from any '63-67 Chevy passenger car.

Set your original sending unit on the bench, un-crimp the pot's wiper housing cover and take a look-see inside to see what's gone 'south'. Effect repair by substituting the damaged component with a fresh used one from a passenger car sender from your local scrap yard and maintain those original pieces that were unique to the big tank sender...

[Jack H.]

An educated guess...

'Tanker' cars are pretty darn rare beasties, but I took a look at the N03 option section of the AIM and noticed there's NOTHING diferent about the instrument cluster. The implication is the electrical function of the tank sending unit is identical to what's used on standard tank cars.

Typically, the differences in sending units deal with mechanical aspects (length and position of float swing arm, mounting of filter 'sock', shape of mounting from the sender flange to the potiameter. That said, I see no reason why you can't 'restore' your original sending unit yourself.

You'll find the potentiameter mounted to the main shaft with a crimped cover that houses the pot's wiper arm and joins it to the sending unit's float swing arm. This is typically where failure occurs.

Either the wire winding in the pot failes by open circuiting or the pot's wiper arm breaks and failes to make contact with the resistance windings. Good used donor parts for the inside 'guts' of the potentiameter ought to be available from any '63-67 Chevy passenger car.

Set your original sending unit on the bench, un-crimp the pot's wiper housing cover and take a look-see inside to see what's gone 'south'. Effect repair by substituting the damaged component with a fresh used one from a passenger car sender from your local scrap yard and maintain those original pieces that were unique to the big tank sender...

[Wayne M.]

Maybe more complicated than that

As you say, the difference is entirely in the tank sender unit, not the dashboard fuel indicator. The signal (maybe 0-90 ohms [not sure]) is probably the same, empty-to-full, but the interior of the potentiometer "pot" has to be different to accomodate the extremely non-linear relation between gallons remaining and float level. A look at the pic below dictates a rapid movement of float arm for small change in volume of fuel when the tank is near empty, whereas once the fuel level is higher than the tool/jack sumps, the float will move very little for large changes in volume of gasoline.

I would expect to see the pot windings widely spaced on the low arm position and closely wound near the top.

Would like to see a close-up pic of the windings on the inside of the pot, if someone happens to try this repair.

[Wayne M.]

Maybe more complicated than that

As you say, the difference is entirely in the tank sender unit, not the dashboard fuel indicator. The signal (maybe 0-90 ohms [not sure]) is probably the same, empty-to-full, but the interior of the potentiometer "pot" has to be different to accomodate the extremely non-linear relation between gallons remaining and float level. A look at the pic below dictates a rapid movement of float arm for small change in volume of fuel when the tank is near empty, whereas once the fuel level is higher than the tool/jack sumps, the float will move very little for large changes in volume of gasoline.

I would expect to see the pot windings widely spaced on the low arm position and closely wound near the top.

Would like to see a close-up pic of the windings on the inside of the pot, if someone happens to try this repair.

[William C.]

You may be giving GM too much credit! *NM*

[William C.]

You may be giving GM too much credit! *NM*

[Dave Suesz]

This is true, but

when the sender and gauge fried themselves in my '55 (musta been a suicide pact) I pulled the sender and gauge out of a 56-ish Chevy pickup. The gauge internals were identical, and the sender mechanicals were close, differing only the the lower part of the 'Vette windings was tapered, like the tank, while the truck was straight. Works perfectly, looks perfect, the only functional difference is the E-1/4 section of the gauge is a bit more sensitive than stock, which is not a bad thing.

[Dave Suesz]

This is true, but

when the sender and gauge fried themselves in my '55 (musta been a suicide pact) I pulled the sender and gauge out of a 56-ish Chevy pickup. The gauge internals were identical, and the sender mechanicals were close, differing only the the lower part of the 'Vette windings was tapered, like the tank, while the truck was straight. Works perfectly, looks perfect, the only functional difference is the E-1/4 section of the gauge is a bit more sensitive than stock, which is not a bad thing.

[Wayne W.]

Re: Too Much Credit

Yep, Bill, he probably is.

[Wayne W.]

Re: Too Much Credit

Yep, Bill, he probably is.