1970 M-M FUEL GAUGE SENDING UNIT

[usmcfred]

Is the standard Fleetwood fuel gauge sending unit the same as the unit required for this (14 gal) gas tank?

Thanks, usmcfred

[fearfair]

I just installed a '77 Fleetwood tank which was the oldest one available as a replacement and a new '77 Fleetwood Sending Unit in my '72 M-M and it works fine with the factory gauge. As to the length of the sending unit, etc. not sure.

I can tell you from experience that most of those universal sending units that you cut to length will not work correctly with the factory gauge.

[Reaper]

This is good to know as my gas gauge for my 72 Caddy is messed up. It goes empty between 1/4 and 1/2 tank. How much was it for you to replace your sending units?

[fearfair]

I think I paid like $69 at Advance Auto..

[Morella]

You can build a calibration box for about $30, that would work at all settings. You would start with an empty tank, and measure the resistance and write it down as you pour in about 3 gallons at a time.

On the bench, set a rheostat with an ohmeter and tape it in place, or use fixed resistors from a variety pack, to simulate the resistance that the float read at each step. I think a 100 ohm rheostat is what I would use. As it changes resistance, you could have a resistor stack, and a transistor stack, and have it switch at each stage. 5-10 stages would do it. You might only need one transistor. There may be a simpler way...that just popped into my head first.

Unfortunately, my psychologist says that I am extremely smart, and I could do this, but it would take me a very long time due to brain damage from accidents; otherwise, I would build you one. It's frustrating, maybe like being really good at basketball and then losing an arm, only worse, because at first glance, it looks easy to me, then my eyes cross and I can't think.

If you have confidence in yourself and use your head, though, you can do it. I once built one to convert Chrysler float to GM gauge by flipping the resistance upside down through a transistor. If you search on "transistor", you can find a good tutorial web page, and it tells you just how to set up a bias network.

Don't pooh-pooh electronics until you've tried it. It's no different than solving a puzzle, or any mechanical engineering or (oh, god dammit, I can't resist), afro engineering that you may have done.

-denise