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smaceng

smaceng

Jedi Knight
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So I replaced the fuel sending unit with one from Moss about 3 years ago and had the gauge rebuilt. Worked fine until recently. Works OK when full to about 3/4 and then goes to empty. Sending unit is suspect. I've run an extra wire to the sending unit for a good ground. Does anyone know if there are any better sending units out there? I have an old OEM one, should I have that rebuilt? If so, by whom.
Thanks,
Scott in CA
 
Hi Scott -

I've lived with the same prob for many years. At best guess (frankly, I've repaired more necessary items and have never gotten around to this one) their is a direct link between individual components (wattage). In other words -- you're gauge and sending unit could be speaking different languages at different intervals on the "full to empty" spectrum. See this link:

https://www.mgb-stuff.org.uk/fuel.htm

I'm real interested in others opinions on this. Luckily I am ready to tackle this item (being I've repair so many items before it that this is the item in more need).

Good luck -

George
 
If it is fairly accurate in the 3/4 to full range then I strongly suspect the sender. It has a resistance wire coil inside with a wiper that is attached to the float that contacts the coil. It sounds like it is not making good contact in part of its range.
 
George, I don't think that I have a problem with early/late gauge and sending unit, as it worked fine (if you can ever say a BE fuel gauge works fine, with it bouncing around all the time) for three years.
thanks,
Scott
 
If there are no issues with the wound resistance wire in the unit it may just be a problem of the contact arm to the wire and you may be able to bend it to get better contact. Worth a look anyway, you can bet the new ones are not the ame quality.

Kurt,
 
The early (pre voltage stabilizer) and later (bimetallic) gauge system parts are not interchangeable. You must have parts that are all from one system or the other. Since you said the gauge had been working fine until recently and suddenly has developed the 3/4 tank problem, this will not be a case of mixed system components.

If the gauge really seems to be working correctly from full to 3/4, the sending unit is suspect. Specifically, there are resistance windings inside the sending unit. If they break, the gauge will for OK from full down to the point the wiper inside the sending unit reaches the break. Once the wiper passes the broken wire the gauge will read empty. Repair is by replacement. The sanity check is to wait until the sending unit shows an empty tank. At that point, run a temporary jumper from the green/black wire on the sender to a good earthing point. If with the jumper wire in place and the ignition turned on the gauge displays "full", the problem is inside the sending unit.
 
Doug, isn't the other problem that the wiper comes away from the coiled wire and doesn't make contact? There are people on ebay that are selling sender units which reportedly have two wipers. Has anyone used this type and is it any better. The ebay seller said that the original Smith sender unit had two wipers.
Scott in CA
 
On early sending units (pre-stabilizer) I believe the normal configuration was to have wipers on both the front and back of the resistance windings. I have not seen that on the later sending units that use the stabilizer.

I have not heard from anyone that the wipers move away from the resistance windings. Perhaps it is possible, but I have not seen it. I have seen broken windings.
 
My experience would be with sending units from other vehicles. The sending unit is simple enough and worth inspecting before ordering parts IMHO. Probably broken windings though.

Kurt.
 
So I received some information back from Moss regarding their Bugeye p/n 361-880, fuel tank sender unit. They said since Winter 2011, this p/n has been improved and uses two sliders rather than just one. Since the one in my car NOW, was purchased from them in late 2008, it is the older design.
In the interest of advancing the breed, I decided to do some research and find out how these things work. I had an old sender unit that I replaced in 2008, so I thought I would take it apart. (THIS IS NOT THE SENDER IN MY CAR TALKED ABOUT ABOVE). This is the result: This sender # Smith FT5300/32 was used with fuel guage # FG 2530/31 at least in my car (1960). When the gas tank is full, the sender reading is about 80 ohms. When the gas tank is empty, the sender reading is about 0 ohms. Which means that the fuel gauge moves to the right as the resistance of the sender increases. So if the sender wire is grounded momentarily, (0 ohms) the gauge reads empty. If the sender wire is removed, the gauge reads full (high resistance). The sender terminal is at the right in this picture. The small wire connected to the terminal in the inside is connected to the coil at the left. Here the float is dropped and indicating an <span style="font-weight: bold">empty tank </span>(low resistance). Note the sliders moved to the left, using very few windings.
 

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Now this picture shows the sliders to the right, which indicates a <span style="font-weight: bold">full tank </span>(high resistance). So what was wrong with this sender and why didn't I use it 4 years ago? All the wires are intact (I think). The sliders are making contact. The brass terminal is OK and the terminal wire is connected. Turns out the slider pivot is not making good contact with the body. If I connect the ground wire right to the float pivot, it works fine. If I connect the ground wire to the body of the sender (aluminum), it is sporatic. What I have discovered is that the Bugeye fuel gauge is just like the one in an MGA. Barney has all that covered in his MGA with attitude website. Cheers, and I apologize for all the tech stuff, but I am an engineer, and it is hard to get it out of my blood. Scott in CA
 

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Barney's site is a wealth of information and a great go-to place for an in depth discussion of the early fuel gauge system.

Prior to 1964 the Mini used the same gauge system as the BE although the actual gauge and sender were physically configured differently. I experienced the same problem you reported with your sending unit above. There were corrosion and fuel deposits preventing the sending unit from getting a good ground path.

As long as the arm is still free to move, the liberal application of spray carb cleaner to the float arm's pivot point and aggressive manual working of the arm generally can dislodge the deposits and restore the sending unit to proper operation. However, you need to continually work the arm and flush the pivot with fresh carb cleaner frequently until you get a good clean assembly again.
 
I R a enge-neer as well and love this stuff!!

Kurt.
 
So I just tried Doug's solution to my problem, and IT WORKED!
I also placed a dimple with a center punch on the outside of the body at the pivot. Good enough I think to stand the pain of removing the tank, again!
Thanks Doug!
Scott in CA
 
Thanks Doug. That was the magical piece of information that just didn't seem to exist anywhere.
 
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