Sending Unit Repair

[adamsanders]

Does anyone know if it's possible to repair a sending unit? It just reads empty all the time. If I unplug the the connector on the tank, the gauge pegs full so I know there is a good connection. From what I've read the sender is just a float attached to a variable resistor. I suppose the float could no be floating but it did move freely when I had it out. On the connector I measure around 16 ohms which correspond to E according to the repair manual. This is with the tank at least 3/4 full. So I know I'm not getting the correct resistance. Any ideas?

 

[riotwarrior]

Replace it

 

[gandalf]

I would agree. If it is the sender itself, and I was absolutely sure it was the sender, I'd replace it. I'm not sure they are repairable.

I'll attach two pictures of a sender from my '92 CCLB Dually.

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[madpogue]

Remove it from the tank and connect it, turn the key to RUN, make sure that tank is selected, and slowly swing the arm by hand. Watch the gauge. If the gauge responds, the sending unit is good and the float is the more likely suspect. As you can see ^^^^^, it just snaps on/off the arm. If no response from the gauge when moving the arm by hand, the sending unit itself is the more likely suspect.

 

[raydav]

Both brass and plastic floats can leak, and then they sink. There is a high pressure point where wire arm contacts the float, and it pokes a hole. I have soldered holes in the brass floats.

 

[mf7lakes]

These guys can fix it.....http://www.tristarrradiator.com/.......

 

[raydav]

These guys can fix it.....http://www.tristarrradiator.com/.......

Or, you can fix it yourself. Ford used the same 10-70 Ohm sender for so long that it is easy to adapt the rheostat from a readily available unit to any tank. One way is to cut the tubes on both old and new a bit below the mounting flange, and use a compression union to attach the new lower section to the old mounting flange.

Also the gauge can be calibrated to read full and empty when the tank is actually full and empty. But first the sender must be calibrated to full and empty. this means removing the tank, and watching inside as it is rolled over, and adjusting the float so that it almost touches the bottom of the tank when upright (empty), and almost touches the top when inverted (full). Empty is more important than full. You can probably adjust for empty by just bending the float rod. Adjusting for both empty and full will probably require adjusting the rod length also.

Then there is the matter of the pickup being at the bottom of the tank. For decades I have replaced whatever screen is on the stock pickup with a piece of rubber hose. And then have a filter you can see into. So then dirt gets picked up and lodged in the filter where you can easily service it rather than clogging the screen, and the screen does not get old and crumble and clog the pickup.

Twice I have gotten sludge that had the appearance of softened, black silicone - once for gas and once for diesel. In the gas car I had a serviceable filter. On a fifty mile trip home from work I had to stop several times and clean the filter. But I got home. If There had been a screen in the tank I would have gone home on a flat bed.

And on both my IDI and PSD I got the filter off the engine and replaced with a Racor on the frame.

 

[mf7lakes]

I do NOT know who wrote the following, otherwise I would give him credit it for it:


I have these numbers saved in a text file, based on info posted on here and at STD over the last 10 years. I haven't verified them independently, but hopefully someone who knows for sure can corroborate or refute these

'80-'86 trucks:

70 ohms empty, 10 ohms full

'87-'97 trucks:

22.5 ohms empty, 145 ohms full

 

[raydav]

I do NOT know who wrote the following, otherwise I would give him credit it for it:


I have these numbers saved in a text file, based on info posted on here and at STD over the last 10 years. I haven't verified them independently, but hopefully someone who knows for sure can corroborate or refute these

'80-'86 trucks:

70 ohms empty, 10 ohms full

'87-'97 trucks:

22.5 ohms empty, 145 ohms full

My 65 Mustang, my seventies cars and my 89 IDI are are all 10-70. I use early Mustang senders senders because they are easy to get. About the time of the PSD the electrical system changed, and not just the resistance values, but the repair fundamentals did not.

The early gauges just heated a bi-metalic strip. The later use a bridge circuit.

 

[franklin2]

My 65 Mustang, my seventies cars and my 89 IDI are are all 10-70. I use early Mustang senders senders because they are easy to get. About the time of the PSD the electrical system changed, and not just the resistance values, but the repair fundamentals did not.

The early gauges just heated a bi-metalic strip. The later use a bridge circuit.

They change around 1987. They work more like the GM models after that.

 

[adamsanders]

I do NOT know who wrote the following, otherwise I would give him credit it for it:


I have these numbers saved in a text file, based on info posted on here and at STD over the last 10 years. I haven't verified them independently, but hopefully someone who knows for sure can corroborate or refute these

'80-'86 trucks:

70 ohms empty, 10 ohms full

'87-'97 trucks:

22.5 ohms empty, 145 ohms full

I have checked resistance across the terminals of my sender. I got ~20 ohms and my truck gauge does indeed read empty. Being a 91, this would back up your info. I haven't got a chance to get into this yet. I'm hoping the float just has a hole in it and is sunk. If not, I will look at adapting a gas sender to work, the diesel ones are hard to find and pretty expensive when you can find them.