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rejuvenating fuel sending unit  Rating:  Rating
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 Posted: 04-30-2014 05:51 am
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Tom Bradley
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(thought I would put my experience here in case it is of help to anyone else)

In getting my JH back running after sitting for several years I had a problem with the gas gauge reading empty even with fuel in the tank.  I tracked this down to the sending unit reading infinite resistance.  Since the insides of the unit are a potentiometer, I decided to try an old electronic technician trick to get it working: WD-40.  What I did was spray WD-40 into the joint where the float arm goes into the sending unit (see pic), then gently moved the float arm back and forth from the full to empty stops.  I had to do this several times before I started to see any electrical conduction at all.  It took about a dozen repeats over several days (leaving time for the WD-40 to work) before I got really consistent behavior with no open circuit conditions anywhere between the stops.  Now it is reading 240 ohms empty and 20 when full, which is about right from what I have read elsewhere here.  (When checking the resistance, have the unit upright, the way it is in the tank--when it is lying down the electrical contact was not as reliable with mine).  It is back in the tank and seems to doing OK so far.  My guess is that any light weight anti-rust oil in a spray can, like Kroil or Liquid Wrench will probably work as well, but WD-40 is the only type I have experience with.  If this does not work, opening up the sending unit container and spraying contact cleaner directly on the contact area might work, but sending it to someone experienced, like DMS might be better.  Unless you are an experienced electronic tech, I would not recommend using any sort of physical contact to try to clean it up.

Attachment: gas guage fix.JPG (Downloaded 170 times)

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 Posted: 04-30-2014 07:48 am
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UKJames
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Thanks for the info Tom.

I've been unsuccessfully trying to source a sender to swap out with one that's not working after a good few years of the car being off the road
I guess where the contact brushes against the resistance wires it has tarnished and gone open circuit.

Did you have any problems getting the sender back in and sealed effectively?

Jim

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 Posted: 04-30-2014 11:25 pm
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Tom Bradley
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The first time I put the sending unit back in I had a leak. I had a new gasket, cleaned the mating surface of the sending unit and made sure that the clamping ring was centered, but did not adequately clean the mating surface of the tank. The place where the sealing happens is beneath the lip where the clamping ring goes. It is difficult to get under there to completely clean out the oxidation and deposits. But once I did that it sealed up nicely without any leaks. I used fine emery cloth and then 600 grit sandpaper for the final cleaning.

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 Posted: 05-05-2014 08:25 am
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UKJames
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Had my sender out this weekend; unfortunately couldn't restore it using WD40- so then decided to open it up (3 tabs need bending up to remove top of can) to further investigate.
It is a simple spring finger that moves against some resistance wire that has been wrapped 100's of times around the board. Really tiny wire, thinner than a hair. The wire had broken away from the stud that takes it to the Faston terminal. Magnifying glass and soldering iron got it going again. While it was apart I also bent the spring finger a little more so it would make good contact. Bench tested with a meter and resistance range was good when I moved the float arm from 'empty' to 'full'.
It was also pretty gunked up in there so cleaned it up before reassembly and refitting.
So far so good...

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 Posted: 01-24-2015 09:21 pm
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mdutch
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Fuel Sender Unit: A little more work today. Got the gas tank out and removed the fuel sender unit. It's complete trash. Rusted solid, main lead is corroded through, looks unrepairable. Are there ANY sources for these, or a suitable OEM part? I hear Delta is out.

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 Posted: 01-28-2015 02:02 am
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Tom Bradley
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I doubt that it is possible to get anything new. You could possibly get a used one from
http://www.britishmasters.net/
Though it will at least require cleaning and will probably not be cheap.

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 Posted: 02-09-2015 10:43 pm
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redracer
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Gents: sorry for not responding sooner; John Tiesler ( JTiesler@woway.com) has done quite a bit of work with a very close replacement:
the Tr7/8, TBS5514 or later, fit nicely with some wire bending and a wider resistance range on the nickel-chromium wire (you can not solder this wire directly, so if your old unit is broken at the tab as many are, unwind one loop to wrap around the post and use light heat to solder to the post, thus "trapping" it).
MOSS LOTORS carries them under part # 071-795 http://www.mossmotors.com/shop/viewproducts.aspx?plateIndexID=33405
but again you will need to modify them slightly:
Here are some of John's notes to me:
A- the jensen is straight but TR7 part is bent. the way the part is positioned in the picture tells me that the bend is going up and forward when installed into full tank, this would be exceptable.
B- the jensen mounting plate is approx 2.5" the same as TR7 part.
C- the dimension of the sender from the plate is the same for both jensen and TR7 part
D- the dimension of the pickup tube is the same for both jensen and TR7 part before first bend of 90 degrees
E- full stop tab and empty tab same on both parts
F- pick up tube after 90 degree bend is 3.5 inch to end of pickup filter, ours is 6.0". would require splice to lengthen the tube 2.5" using a piece of rubber fuel line hose and clamps. ( should work)
G- the distance from the plate mounting to the center of the float is 7.5". appears to be same for both jensen and TR7 (before bending float rod).
should not be a problem if it is shorter.
H- this is the position of the float after bending at the mid point of float rod, straighten the float rod to put the float barrel it the same height as the end of the jensen full pickup filter. this would show the empty position for the sender.
J- this would be the travel distance from empty to full for the float barrel ( shown after bending ) of 9". the current tank is about 10" high so the full gauge reading would be similar.

DELTA sends rebuilt ones(you'll need to send them your old one for a core charge) that will be ready-to-go at a higher price, but it's your call and time.
best to everyone, bruce madden

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 Posted: 02-10-2015 04:38 pm
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John Young
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MARTIN ROBY HAS THE FUEL SENDNG UNIT LISTED ON THERE WEB SITE.IT IS PRICED AT ABOUT 65 http://www.martinrobey.com/images/products/91169_220.jpg
REGARDS JOHN

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