Gas Tank Sending Unit Trouble Shooting
 

Thought I’d share some findings I discovered tonight. My fuel gauge has never worked as long as I have owned my Chevelle. My plan was to remove it and send it to a shop here in Ohio for a rebuild. I decided to check the resistance with my multimeter to see what was what.

1st up I noticed that I had an open circuit (1st photo) when I touched the multimeter positive probe to the sender post with the float at its empty-tank position. When I flexed the probe to one side or the other I was able to read a low resistance (.9 ohms) intermittently (2nd photo). Then with the probe flexed to the side i was able to get a reading of about 92 ohms with the float at the full-tank position (3rd photo)....

Where the stud goes thru the sending unit it usually looses connection. I have taken the push ring off wire brushed everythig and put it back together and then it works fine.

On the under side of the post I noticed the retaining nut was corroded. This nut (1st photo - green arrow) is responsible for making the connection between the post and the conduit (2nd photo - blue arrow) that connects to the float mechanism that measures resistance based on the float position. i disassembled it and found that there did not appear to be a good connection with the conduit that connects to the float mechanism. I cleaned up all metal contacts at this junction and made a new rubber gasket (2nd photo - green arrow) to electrically isolate the post from the sender frame. The old gasket was deformed and too thin (2nd photo - red arrow). Once this was done the connections worked just by touching the multimeter probes to the sender post and the ground wire. I am hoping this has fixed my problem. I’ll hook the sending unit up to the gauge lead tommorow before reassembley to ensure the sender is sending a good signal to the gauge.

Ha, you beat me to it!!:laugh:

Never have I done what I am about to suggest, but do you think a little solder on that whole pin, nut, wire area would insure this would not happen again and prevent corrosion at that point? I just believe that that if I have to fix something, I’m going to fix it for good ‘ cause I don’t want to have to do it again. As a disclaimer- I am a purest and want things correct. I also don’t want to re-engineer what GM did, but something unseen and if I can make it better, (even if it is just better in my mind) I’ll try. I probably put too much thought into stuff?
BTW Sam, great diagnostic skills!

Bentley - the same thot crossed my mind. IMO, this is a simple, but poor design. It creates a high likelihood that corrosion will play havoc on the system. I think solder might do the trick. Thanks!

You have to remember, GM did not intend these things to last 50 years, so the design may leave a little to be desired :wink:

I know John suggested the same thing when I had problems with the sending unit on my Post Sedan. I could not get that push nut thing off to save my soul, it just dug in more when I tried to remove it. With all the fragile components on that sending unit, I figured I was going to end up doing more harm than good, so I just sent it off to John Wolf & Co. in Willoughby OH and they fixed it up good as new. I am now having the same issue with my convertible, so I might try this again when I get around to fixing it.

Bill one of the times i did it i cut the retaining ring off and bought a new one I think Ace hardware has them

Test complete. Float in down-most position. Float in up-most position. Right as rain! :cool2:

Good info Sam!