Fuel gauge issue 1940 Special

[Robby120113]

Goodmorning,

 

my fuel gauge is working only for the last quarter. That the most important part luckily. But how can i get the full range again. 
 

thanks for the tips

[rodneybeauchamp]

On my ‘38 I found the spiral resistor wiring had failed so the gauge was giving false readings and flicking violently at a certain level. After removing the gauge, was able to make one out of two from a ‘37 unit and now have a reliable gauge back in there. Cleaned the tank out at the same time, so double bonus. You may be able to repair the old one with some care or locate a second hand unit off the forum.

good luck

Rodney 😀😀😀😀😀😀😀

[37_Roadmaster_C]

Please give us a more detailed description of the failure. For example: the gauge reads correctly when the tank is between 1/4 and empty. When over 1/4 full the gauge reads xxxx (full or empty).  1930's GM gauges read full when the tank sender wire is open and empty when the tank sender wire is shorted to ground. A full description will tell us what is happening electrically.

[Matt Harwood]

Sounds like a sending unit problem simply because it works correctly from 1/4 to Empty. The resistor is failing or the float arm is damaged somehow. I don't know for certain but I believe the sending unit is the same as the '41, and they're commonly available. The Buick suppliers sell them for $75 but Summit Racing sells the exact same one for about $35 (https://www.summitracing.com/parts/tnk-b1-s). I'll wager that's your problem.

[Robby120113]

It is indeed not going further up then 1/4. To replace the fuel sender does the fueltank have to be removed?

thanks for the tips

[neil morse]

1 hour ago, Robby120113 said:

It is indeed not going further up then 1/4. To replace the fuel sender does the fueltank have to be removed?

thanks for the tips

 

Yes, you have to remove the tank to replace the sender.  Here's how I did it on my '41.  Not too difficult. (Click on arrow in upper right hand corner.)

 

 

[kgreen]

Yup, If Matt hadn't noticed your post I would have directed you to a thread of his with a discussion of his replacement.

[neil morse]

14 minutes ago, kgreen said:

Yup, If Matt hadn't noticed your post I would have directed you to a thread of his *with a discussion of his replacement.*

 

Matt is irreplaceable as far as I'm concerned.  😄

[Morgan Wright]

The sending unit is has a cork float. If it works part of the time something might be wrong with the cork.

 

You can get a new cork from a bottle of wine. Very easy, but you need to remove the tank to get to it. That's what the wine is for.

[Bloo]

If it's cork, and you use the one from the wine, don't forget to seal it first. Gas tank sealer might work. Bob's has pre-sealed corks as an alternative.

 

1937 Buick still used a cork. Did 1940?

[Morgan Wright]

37 minutes ago, Bloo said:

If it's cork, and you use the one from the wine, don't forget to seal it first. Gas tank sealer might work. Bob's has pre-sealed corks as an alternative.

 

1937 Buick still used a cork. Did 1940?

 

Yes I had a 1940 once

[neil morse]

The original sending unit on my '41 used cork.

[Robby120113]

Then i have to make time and motivation to take the fuel tank out. Thanks all

[Morgan Wright]

1 hour ago, Robby120113 said:

Then i have to make time and motivation to take the fuel tank out. Thanks all

 

The only thing holding the tank in is 2 steel straps. One or two nuts on each strap and it falls out, especially with help from the weight of 15 or 20 gallons of gas.

 

Only kidding. Empty the tank first. 

[Bloo]

You'll need 2 corks.......

 

[Morgan Wright]

4 hours ago, Bloo said:

You'll need 2 corks.......

 

 

??

[2carb40]

13 hours ago, Robby120113 said:

Then i have to make time and motivation to take the fuel tank out. Thanks all

On my 1940 Super coupe there was an interesting circular pattern stamped in the trunk floor right above the circle of bolts needing  to be removed to take the sending unit out of the tank. Used a hole saw to remove trunk metal and made a circular access panel for servicing sender and wire when and if needed, rather than having to deal with weight and bulk of tank removal. Covered with trunk matt. Adjust centering drill bit on hole saw to just barely enuff sticking out. Hole in trunk metal yes, hole in top of tank, no! Good luck! Run drill in reverse when using holesaw in sheet metal.

Edited September 28, 2020 by 2carb40 (see edit history)

[Morgan Wright]

Taking the tank out is real easy. Simple job.

[neil morse]

8 hours ago, Morgan Wright said:

 

??

 

 

I think this is what Bloo meant when he said you'll need two corks.  This is the original sending unit from my '41.