Where would you start troubleshooting a faulty gas gage? When the tank is full, it bottoms out past the F mark. It stays there until that tank is at about ¼ full. Then it goes to where it should be and stays accurate until the tank is almost empty, then it goes back to the far right past the F mark again. Any ideas anyone?

 

Sender maybe? They work off ohms transmitted to the guage. I guess you could take out the center guage cluster and hook up a meter to get readings at different fuel levels. Somebody correct me if I'm wrong on this. I think its 90? ohms at full tank? If it checks out right then I guess the guage is bad. Replace it with a digital one once its out. I'll check my service manual and see if they have a procedure.
ESU

 

I bet it is the sending unit located in the gas tank.

 

How hard is it to replace the sending unit?

 

Have to drop the tank I imagine. I did my Bronco once, was located on top of the tank, had 2 or 3 wires attached then a float in the tank. Might as well change the gasket while ur at it.

 

Not sure on year, but on my 76 i just had the tank down becaus my gauge did not work. I pulled the sending unit, mine was on the top of the tank. Removed bolts that surrounded the filler hole, and the sending unint comes out attached to the filller hole. I did find that the float on my sending unit was hitting a baffle that was attached to the whole assy. I had to bend the rod the float was on to keep it from hitting the baffle. No idea how it could have gotten that way. Just never know what you will find when you take something apart. I also found out my ground on the top of the tank was not making a good connection, pretty corroded.
Good Luck

 

What year is your Vett? I have a 74 and the sending unit is is the bottom and very easy ti change, but I think this is a one year thing.

 

I have a 74,Gas guage read 1/4 tank when full, replaced sending unit which is on bottom,very easy,but still read 1/4 tank. I replaced guage which solved my problem.

 

'63 ~ '74 - sender @ bottom of tank

'75 ~ '78 - sender @ top of tank

'79 ~ 82 - (different) sender @ top of tank

 

Here's the post you've been waiting for. You can replace your sending unit for $140 or you can fix the one you have with a piece of 000 steel wool and an hour of your time, and you don't even have to drop the gas tank.

My guage read exactly as yours does. A couple weeks ago 80TexasC3 told me how to fix it. Here is how I did it:

1. Remove the gas filler door by taking out the four screws that hold the lower portion to the body.

2. Remove the rubber filler neck surround. Now the top of the sending unit is visible.

3. Remove the electrical connections.

4. Remove the three fuel lines (fuel line, return line and breather)

5. Remove all the bolts holding the sending unit to the tank.

6. Gently lift the sending unit. Be careful because there is a gasket between the two that could be rotted out and debris could fall in the tank. (I got lucky, mine was in perfect condition)

7. Turn the sending unit 180 degrees and gently pull out of the tank and gas door hole in the body of the car.

8. With the sending unit now out of the car, you can see a silver box in the middle of the pickup tube where the float pivots. There are three tabs that are folded over the cover. Bend those back and pop the cover off. Inside is a coil that is covered in varnish. Take your fine steel wool and starting rubbing the coiled pickup to clean the varnish off. Clean the contact on the sending unit arm as well.

9. Put it all back together in the reverse order you took it apart in.

 

I would like to thank you guys for your input but specially thank Ak. Mal for his more than detailed how to procedure. Mine is an 80 C3 also. Boy I love this forum......

 

Will this work on '75 -'78 also? I believe '79 - '82 use a different sending unit.

Thanks,

 

I'm sorry, but that is a question that I do not have an answer for.