73 duster - gas gauge not working

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plyduster73 said:
So I took the electrical plug off the tank, put a screw in it and ground it to the brake line. See photo.

The gauge moved all the way to full!

While I was under the car and had a good grounding position, I took the clamp and hooked it to the tank and reconnected the electrical plug to the tank also...nothing happened this time.

Also on a side not the electrical plug was wet with gas, so im assuming the rubber seal is rotted?

So with this info I am assuming that the sending unit is bad?
Click to expand...

Exactly.
Good job

When you put the new sender in use the new seal with the old retainer ring.
The new rings are usually thinner and don't seal as well.
When I did mine I put a little silicone on the tank side of the seal so it would stick in position while putting the sender in.
 
Thanks for all the help and info guys.

Now to order a new sending unit.
 
Just a thought here. My brother ordered three "new" fuel sending units from various restoration suppliers and never got a good one. They are all Chinese crap and after we spent the third weekend in a row under his 1971 Barracuda swapping them out he decided to send the original American made unit to http://www.gaugeguys.com/ and have it fixed. They charged him $80 plus shipping and it works great.
 
Got mine from Jegs, and it looks like it's built ok and it works perfectly.

We'll see though, right? :D
 
mopardude62 said:
... They are all Chinese crap and after we spent the third weekend in a row under his 1971 Barracuda swapping them out he decided to send the original American made unit to http://www.gaugeguys.com/ and have it fixed. They charged him $80 plus shipping and it works great.
Click to expand...

Just swapping parts does not determine "root cause". For those that don't own a multimeter and refuse to get one - please stop asking for help with electrical issues. Note that I didn't even say "buy" because you can "get" one free at Harbor Freight.

I find it hard to imagine that 3 new senders are all "Chinese crap". One should verify that each component is doing its job. For the sender, what is the resistance between terminal and the body as the arm moves from low to high? I would never install one without checking that against factory specs. Many things can keep the dash gage from reading correctly. At the sender end - float doesn't float, bad ground of sender body, bad output connection, resistance change is wrong.
 
The problem is in the aftermarket senders for some models.
For many years these S-W/Chrysler gauges operated on 20 ohms internal resistance. In 1970 the fuel gauges changed to 13.5 ohms internal resistance. That meant the sender had to change also. The Chinaman doesn't know any more than he is told so his senders match one type gauge but not the other.
Aftermarket sender in my 67 fish still works perfectly after 5 years.
 
Ill check the ohms while im at it, so with a 73' Im looking for 13.5 ohms?

The jegs unit is 40 bucks, I don't mind spending a little more upfront if I can get better results or longer life out of a different unit.

Since mine was a /6 car I can pretty much bet on the smaller fuel lines when I order, right?
 
plyduster73 said:
Ill check the ohms while im at it, so with a 73' Im looking for 13.5 ohms?

The jegs unit is 40 bucks, I don't mind spending a little more upfront if I can get better results or longer life out of a different unit.

Since mine was a /6 car I can pretty much bet on the smaller fuel lines when I order, right?
Click to expand...

Depends on where the arm is. That seems to be the big complaint with repops---they don't seem to be accurate.

You can bend the arm so it's accurate at MT but it might show 3/4T when tank is full.

Only advice I can give you is install the sender........pour a little fuel in until you can siphon fuel out of the outlet, and then check resistance. MT should be 73-75 ohms or so. Bend the arm until you make that.

Full is about 13, 1/2T is 23--25, and MT is 73-75 ohms.
 
13.5 +/- .5 across the gauge would be correct for the 73 model.
A 10<->80 sender will show about empty and about full in most cases.
It's hardly relevant to how much fuel is actually onboard though.
The earlier 20 ohm gauges will move their needle at 1 ohm increments changes at the sender. There isn't enough heat generated in the later gauges to do that. In fact, engineers changed the needle pivot design to compensate for the weaker movement.
If you know your sender is bad, just ignore all this technical stuff about the gauges for now. Buy a sender and see how it works. Good luck
 
Im ordering the sending unit now but I wanted to know what you guys thought about getting the larger size fuel line choice.

Mine is the smaller line but I plan on going with larger motor (360) in the future.

Would I run into problems if I got the larger size and then necked it back down until I got the cash up to just redo all the lines bigger?

Or will a 360 run fine on the small lines?
 
plyduster73 said:
Im ordering the sending unit now but I wanted to know what you guys thought about getting the larger size fuel line choice.

Mine is the smaller line but I plan on going with larger motor (360) in the future.

Would I run into problems if I got the larger size and then necked it back down until I got the cash up to just redo all the lines bigger?

Or will a 360 run fine on the small lines?
Click to expand...

Get the larger one now, and you won't have to wonder why the car won't accelerate right when it has the 360 in it. :D
Necking down won't be a problem.
 
67Dart273 said:
Depends on where the arm is. That seems to be the big complaint with repops---they don't seem to be accurate.

You can bend the arm so it's accurate at MT but it might show 3/4T when tank is full.

Only advice I can give you is install the sender........pour a little fuel in until you can siphon fuel out of the outlet, and then check resistance. MT should be 73-75 ohms or so. Bend the arm until you make that.

Full is about 13, 1/2T is 23--25, and MT is 73-75 ohms.
Click to expand...

It took me a while to figure out that "MT" means "empty". I was looking for a mnemonic.

When I had a problem on my 67 fish I took the old sending unit out and was able to bend the metal of the resistor arm so it contacted better and it worked great. Sometimes this works and you can save a bit of time.

I also changed the screen on the pickup tube at the same time.
 
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