The Stovebolt Site Forums The Shop Area The Electrical Bay Sending Unit 52 Chevrolet pickup 3100 series

All,
I have a specially built fuel tank under the bed, in the frame of my 1952 3100 series. We have installed three sending units and they get fried! The last one was tested in each stage of it being installed, from start to finish. All three have worked for about 2 hours of drive time or so then pegged the needle.

Any thoughts on what could be causing this?
I know a bad ground can be an issue....
Thanks everyone for taking the time to help me out....

need more info, usually it'd be the gauge that gets fried .... 6V or 12V? original gauge? correct ohm rating for gauge?

Bill

Fried? Or is the Resistance wire coming apart? You might have too much road shock with the present mounting or some cheap sending units. You most likely have a wire that is getting pinched and shorting the sender to ground.

I am the one doing the work on it and have a couple other threads/comments about this problem.
The sending units (2 of the three)are 30ohm units from Macs, the first one I thought I fried while welding some straps onto the new gas tank to secure the gage wire & fuel line. I testing the unit thoroughly when I set the sending unit in it and when I had everything together the gage quit working. I had to tear the bed off etc and replaced the sending unit (another macs), tested it thoroughly and put the bed back on etc and it worked for a while befor quitting. I pulled the bed and found it fried just as the other one that I thought I had ruined welding. I bought a different sending unit (RCI), tested it thoroughly and put the bed back on and it lasted for a while and has quit. I'll have the truck by the weekend and we'll see whats' what.
The gage is an autometer.
The other senders were fried, the copper winding had turned blue from the current. I can't understand how it is happening because they are just a basic wheatstone bridge circuit and only milliamps can flow until the needle and sender resistance become equal.
If any of you guys have any idea - serious or bazaar - speak up, thanks oj

maybe you have the power to the wrong terminal on the gauge ... hey wait, isn't an Autometer gauge higher resistance?

Bill

Isn't Macs a Ford supplier?

Yes, you're right. The sender came from LMC - at the same time I was working on a '48 Ford F3 and had a nasty time of it with Macs' stuff not fitting and working right.
Autometer offers 3 different fuel level ranges, the one I chose was 0-30ohm and it tested proper with the sending unit in hand operating thru its' range. I would've bought the sending unit from autometer but they don't offer one for that range.
Keep the thoughts coming, they are helping.

Isn't Frawds of that era positive ground?

I've seen everything now!
The truck arrived a few days ago dripping fuel out of the tank onto the bed of the rollback, I could see what looked like a puncture. By the time it was unloaded the tank was empty otherwise I'd never had known the tank had a leak and would've pulled the bed to replace the sending unit.
Pure luck it was leaking.
I crawled under to find a pinhole in a brandnew steel tank, I cleaned around the hole and saw a blueish halo around the hole. When the muffler guy welded the muffles (they run right under the tank)he missed with the mig wire and ran it into the tank! That was what shorted the other sending unit! The tank didn't leak until it was filled completely after it left my shop.
I patched the hole and just put some gas in it and the gage reads proper without leaks!
Pure luck that it leaked when they delivered it, if all the fuel had run out i'd never have known about the hole and would've pulled the bed off, removed a perfectly good sending unit and would've been totally dumbfounded.

Lucky welder!

So if I understand it properly, there is now a functioning gas gauge in a truck that has mufflers that run just under the gas tank. I hope the mufflers never develop a leak or over heat!