56 special gas guage help!?!

**frankdtank** · 11-24-2012, 01:32 PM

I finally got to take my first drive down the road yesterday in my 56 special, which was KILLER. One of the many things I noticed is that my gas gauge is stuck at 1/4 tank. I'm assuming that since its on 1/4 tank and not reading full or empty the gauge is bad. I tried to pull the brown wire from the back of the gauge and turn on the ignition hoping the gauge would move, but nothing happened. Does anybody have any advice or know where to get a replacement?

Edit: I forgot to mention that the gas tank and sending unit were just replaced.

**frankdtank** · 11-26-2012, 03:13 PM

I took the gas gauge out and it seemed ok. The needle slowly moved as i rotate the gauge but just sits on empty when connected. I tried doing a straight grownd to the gauge and the needle moved. I was surprised when it only moved to a 1/4 tank and not full. The fuel tank sender I ordered was a 0- 30 ohm if that's helpful at all.

Does anybody know how to test the gauge? I'd like to see it read full before putting it back in. I assumed the straight grownd would do the trick. Also, any advice on further troubleshooting?

**raycow** · 11-26-2012, 04:45 PM

Originally Posted by frankdtank

Does anybody know how to test the gauge? I'd like to see it read full before putting it back in. I assumed the straight grownd would do the trick. Also, any advice on further troubleshooting?

Ground the gauge housing or mounting plate. Apply +12V to the power terminal and the pointer should go to full or beyond. Now ground the sender terminal and the pointer should go to empty or below.

Ray

**frankdtank** · 11-26-2012, 06:28 PM

Originally Posted by raycow

Ground the gauge housing or mounting plate. Apply +12V to the power terminal and the pointer should go to full or beyond. Now ground the sender terminal and the pointer should go to empty or below.

Ray

That was exactly what I needed. The gauge worked exactly as you described. What a relif I don't have to replace it. So it must be something with the sending unit. I did a little research and I read the sending unit needs to be grounded, but the other tank and sending unit didn't have a ground wire attached. Looks like I might have to drop the tank again.

**raycow** · 11-26-2012, 08:56 PM

Originally Posted by frankdtank

I did a little research and I read the sending unit needs to be grounded, but the other tank and sending unit didn't have a ground wire attached. Looks like I might have to drop the tank again.

The possibilities are a bad sending unit, a bad ground at the sending unit, or a bad wire (open or shorted) between the dash unit and the tank.

Check the wire first. Disconnect it from the sending unit and the gauge should read full. Ground the wire and the gauge should go to empty.

Ray

**frankdtank** · 11-27-2012, 09:07 AM

I'll have to wait unit the weekend to drop the tank and troubleshoot it more. I'm assuming that if everything tests out OK, I'll have to add a ground wire to the sending unit. Since the tank will be down, do you need to typically need to adjust the float arm to ensure its reading the correct level or are they usually correct to start with since its new? Thanks for all your help Ray!

**raycow** · 11-27-2012, 09:38 AM

Originally Posted by frankdtank

do you need to typically need to adjust the float arm to ensure its reading the correct level or are they usually correct to start with since its new?

No calibration is needed on the original factory sender, but you did hit on one of the reasons a lot of senders get replaced. The float, which is made of two brass stampings soldered together, can develop a leak and fill with gas. It then no longer floats, which causes the gauge to read low. A leaky float can be repaired and returned to service if the sender is otherwise good. Some people replace the original brass float with a cork or plastic float that can't leak.

Ray

**frankdtank** · 12-02-2012, 05:59 AM

I dropped the tank yesterday and after checking the wires, I traced the problem to the ground wire at the sending unit. I find it a little strange that the sending unit I replaced did not need a an additional ground wire. It must of grounded through the tank somehow, but its working now and that's all that matters.

Once again, thanks for your help.

**raycow** · 12-03-2012, 02:09 AM

I'm glad to lear you were able to locate the problem and fix it.

As built, the sender was grounded only through the tank mounting. This worked fine when the car was new, but after 50+ years (and sometimes a lot less) corrosion and dirt could degrade the connection to where you would often need to run a separate ground wire. If yours works without it, consider yourself fortunate.