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Since the sender is basically a variable resistor, it doesn't care whether
it's hooked up to positive or negative earth. I don't know all of the
options for replacement senders that are out there, but I can say a few
words about the one for BJ8s available now from Moss Motors (p/n 021-571)
based on personal experience. I think this unit is made in Taiwan, but I'm
not sure.
The one I received worked fine for about three days, then the gauge
registered permanently empty. The problem was the plastic float that came
with the new sender had a small crack in it, the float filled up with fuel,
and sank. Moss sent another complete new sending unit and float, but on
inspection I could see that the float had a HOLE in it. Both the crack in
the first float and the hole in the second were at the end of the wire float
arm. I have since learned that others have had this same problem. I
believe that damage to the float is caused by the sharp end of the float arm
wire when the float is clipped into it.
Thanks to lister Robert Barback, I found a solution today. He told me that
a Ford float, part number COAZ-9202-B, would work. This afternoon, I went
by my local Ford dealer and discovered that for $4.14 the part number will
get you two BRASS floats, identical in every other way to the plastic floats
supplied by Moss. I also took the precaution of bending the end of the
float arm wire back slightly to avoid its digging into the float. That
might be useful to anyone else who has occasion to order a Moss sending
unit.
Happy Healeying!
Steve Byers
HBJ8L/36666
Havelock, NC USA
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Fuel Gauge Tech Tips
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To test the gauge : turn on the ignition and then disconnect the wire at the sender.
The gauge should go to to the "Full" position. Touch the wire that goes to the
sender to ground and the gauge should go to "Empty".
If these tests are correct the fault is in the sender if not repeat the tests using
the "T" terminal of the gauge and a jumper wire. If now OK the fault is in the
wiring to the gauge.
If not OK the fault is in the gauge or the power supply to the gauge.
Looking at the back of the gauge with the terminals at the top; the left terminal is
the "T" (Tank) terminal.
Hope this helps.
--
Regards,
Mike Salter
http://www.precisionsportscar.com/
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After the recent discussions about jumping fuel gauges needles, it got me thinking, particularly the point about a bad earth I looked at all the possible earth connections, glued in screws (sender to tank), tank straps with rubber strips underneath and the other was the fuel take off and line, neither of these providing a strong earth connection. I have to report that after making up an black earth cable and fitting it to the sender unit base all is ok. At least I get a much less flickering needle and one that moves more progressively when detecting differences. The difference was amazing.
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Flutter of the fuel gage is usually caused by poor contact between the
sweeper blades and the wire coil int he sender unit. This is easy to verify
by removing the sending unit and checking its resistance with an ohm meter
while moving the float arm. You'll need to move the arm slowly as digital
meters take readings at intervals and you need to see successive readings to
tell what's going on. Analog meters (with dial faces and a sweep
needle/pointer) will show the changes in resistance a bit easier.
Anyhow, it is not likely that the sweep arms have lost their pressure against
the wire coil Rather, the wire coil has gotten dirty and the arms lose
contact as they sweep along its sides. Before trying to effect any repair,
you MUST understand the design and materials used.
First, the wire is extremely fine laquer-coated copper, coiled in one layer
around an insulating tube/core. If you envision a crossection of the coils
nesting next to each other, each insulated from the next by the lacquer
coating. The top "surface" of the coil has peaks and valleys as you move
from coil to coil. In manufacture, the peaks are sanded lightly to remove
the lacquer coating and expose the copper wire. This does not short out
between coils, but merely lets the sweeper blade touch their outer surface.
One end of the wire is soldered to the terminal post. The other end has its
insulation stripped from about 1/4" and is jammed between the insulating
collet/sleeve (that the "hot" post passes through ) and the metal body. It
is extremely important that you have a good ground between the body/gas tank
and car or the sending unit won't work.
At "full" position, I believe the total resistance is around 85 ohms, and at
"empty it is around 2 ohms. Make sure your ohm meter leads are making good
contact tot he "hot" post and unit body when you check the resistance.
If the resistance jumps around as you sweep the float arm, then to clean the
coils Isuggest the following.
1) Remove the lid. NOTE: all screws on the unit are BA thread (and the six
attaching it to the tank as well), so don't lose them! Also, try to avoid
damaging the gasket, though this can be replaced if needed.
2) Use a very find wet/dry paper and cut a little strip about 1/4 - 1/2"
wide. I would use 1000 grit. Also, get a thin piece of brass or steel shim
stock to use as a support to press the sand paper against the side of the
coil.
3) Position the sweep blades at one end of the coil and work on the far
"half". Gently move the 1000 grit paper, backed by the brass shim back and
forth across the coils. A few sweeps should be enough. Remember, if you
sand away too much of the "peaks" you can end up with adjacent coils shorting
to each other. You're just trying to clean up the coil's swept surface.
Place a piece of 1000 grit paper along the full length of the coil, with the
grit facing the sweep arm. Move the arm to clean its rubbing surface. Do
this to the other side as well.
Two cautions:
1) Watch out for the stand of coil wire that runs from the he far end to the
front. If you break the wire you've created a tougher "fixing" problem.
2) Do NOT use any lacquer thinner to clean with. This will dissolve the
insulating coating. You need to keep things dry.
Use compressed air to blow all grit out. Retest with the ohm meter. You
should see a fairly steady change in resistance as the arm is moved from one
extreme position to the other.
Put the lid back on, making sure there is a good gasket.
Roger Moment
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