Cherokee Fuel Gauge

When I had my tanks out in 1999 for the paint job and hose replacement,
I also noticed stains from the sending units downward. I decided to
replace the gaskets and reseal the things "while I was at it". The local
wrenches said that getting the screws around the sending unit to seal
completely was a crap shoot and the recommended method was to coat them
with fuelube. They also said they were trying out using statoseal
washers on the screws in an attempt to keep the screws from leaking.

When I had the sending units out, I noticed that the resistive element
had holes for rivets at both ends, however, only one end was riveted on
both sending units. I thought it was odd but was not about to
"experiment" by replacing the other rivet. My mechanic agreed. What was
also odd was that the resistive element could wiggle back and forth
pivoting on the single rivet. It struck me that eventually that would
break from fatigue. But, I found no remnants of rivets in either tank
and was hesitant to do any modification to this important system.

Put everything back together and all worked fine for about 3 years or
so. Then, the right gauge began reading about 2-3 gallons lower than the
left gauge with a level plane and the same amount of fuel. It continued
to read low by anywhere from 2-5 gallons low for about the next 2 years.
Then, one day, the right gauge read 0. Really less than zero and on the
peg. Getting out the repair manual, I saw that zero resistance should
send the gauge to the "full" peg. I briefly grounded it and it did jump
to "Full". For the next year, it worked as it had (around 4 gallons
low). LAst couple of flights, it began reading all over the place, from
less than zero to a few gallons low. Again, I briefly grounded the gauge
and it flew up to zero. But this time, if remained flaky and is reading
all over the place.

By switching the sending units to the opposite gauges, the problem
appears to indeed be with the right sending unit (or the wire from the
terminal block to the sending unit). Checking the blade connector at the
wing did not have any effect.

I cannot remember if there was enough of a hole to get at the wire on
the sending unit when you removed the inspection panel at the right
landing gear. My hope is that the wire has worked loose at the sending
unit terminal. I seem to recall JUST being able to touch the terminal if
I put my arm in it up to the elbow (and it was NOT easy).

Anyone else have any experience with these critters? Are they supposed
to have 2 rivets holding the resistive element(one at either end)? Can
you get at the terminal without pulling the tank? Are new sending units
available for a reasonable price (maybe $200 or so)?

Thanks for any suggestions. Please restrict any feedback to actual
experience.

Mike

Have you run the tank dry/drained it and looked at the float/sender with
a flashlight and mirror while moving it with a stick and watching the
fuel gauge/ohm meter?

take the unit out , call air parts & they will fix the sending unit
800-443-3117
hopes this helps

I seem to recall reading a suggestion somewhere that if you have your
tanks removed and opened for any reason, you might as well replace the
senders because it's a relatively cheap part that's hard to get at
normally.

Not to hijack the thread, but does anyone else have an opposing
viewpoint or more data on this?

Thanks!

Ben Hallert
PP-ASEL

On 11 Jul 2005 19:48:47 -0700, "Ben Hallert"
wrote:


Not to hijack the thread, but does anyone else have an opposing
viewpoint or more data on this?

The Cherokee 235 BB is at:

http://www.cabo-rental.net/cherokee2...n ch&number=2

Search the site for fuel sender.

Don

No. This puppy will read up and down several gallons and/or around
several "ranges" when the plane is motionless. That seems to suggest a
ground problem.

The common failure modes folks report a float detached, bad ground at
the gauge, bad ground at the sending unit, broken resistive element.

A detached float or bad element would suggest zero readings all the
time. A bad ground at the gauge would make the error follow the gauge,
not the sender (as I have isolated). That leaves a bad ground at the
sending unit. This may be the problem. The statoseal washers did tend to
isolate the mounting screws from the sending unit. The sending unit is
further isolated from the tank via the gasket. Whatever ground I may
have had initially may have corroded/eroded away. I may be able to snake
my arm up the inspection cover for the landing gear to get a grounded
wire on the back of the sending unit.

A new sending unit is listed at $237, however, the usual places don't
have any. Some suggest there are no new ones available. I don't want to
send the thing out for overhaul if it turns out to be defective and I
don't trust boneyard parts for this type of thing (they are ALL worn out
and 35 years old). I would prefer to have a new one, or, if that is not
possible, an overhauled unit standing by for a quick swap.

Thanks,
Mike

john smith wrote:

Have you run the tank dry/drained it and looked at the float/sender with
a flashlight and mirror while moving it with a stick and watching the
fuel gauge/ohm meter?

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Yep, a little information.

Last Feb, the right fuel guage in my Cherokee 180 dropped to zero. We
pulled the tank and found the float had "disappeared" from the sending
unit arm. Closer look into the tank turned up the two pieces. CHEAP
piece of plastic that had broken in two.

I know this cheap piece of phenolic plastic (or whatever it is)
couldn't cost more than 25 cents to manufacture. But since its "an
instrument", you can't just get the part to stick on yourself. You
have to ship the sending unit to an authorized repair station to stick
a 25 cent part on it, test it, yellow tag it, and bill you $75+ for
the job.

But in my case, they screwed up -- didn't read the instructions with
the sending unit, didn't remember our phone call, and rebuilt it. The
cost if I remember right was right at $150. A phone call straightened
that out and got the overcharge back on my credit card. But that's
what the rebuild cost was.

Air Parts of Lockhaven, Ct. Look them up on the web, they're there.
Phone number is 800-443-3117..

Oh, and good luck finding a competitor to compare prices. They were
the only place I found doing floats/sending units.

See attached picture of rebuilt sending unit. I can't tell what
rivet(s) you are talking about. Hope you can see them on that
picture, its the only good pic of the unit before I installed it.

Oh, and don't forget to get a new gasket. They'll throw away the old
one when you ship it to them for rebuild. You'll want a new one on
hand when the unit comes back.



Chuck




On Mon, 11 Jul 2005 23:10:08 GMT, Mike Spera
wrote:

When I had my tanks out in 1999 for the paint job and hose replacement,
I also noticed stains from the sending units downward. I decided to
replace the gaskets and reseal the things "while I was at it". The local
wrenches said that getting the screws around the sending unit to seal
completely was a crap shoot and the recommended method was to coat them
with fuelube. They also said they were trying out using statoseal
washers on the screws in an attempt to keep the screws from leaking.

When I had the sending units out, I noticed that the resistive element
had holes for rivets at both ends, however, only one end was riveted on
both sending units. I thought it was odd but was not about to
"experiment" by replacing the other rivet. My mechanic agreed. What was
also odd was that the resistive element could wiggle back and forth
pivoting on the single rivet. It struck me that eventually that would
break from fatigue. But, I found no remnants of rivets in either tank
and was hesitant to do any modification to this important system.

Put everything back together and all worked fine for about 3 years or
so. Then, the right gauge began reading about 2-3 gallons lower than the
left gauge with a level plane and the same amount of fuel. It continued
to read low by anywhere from 2-5 gallons low for about the next 2 years.
Then, one day, the right gauge read 0. Really less than zero and on the
peg. Getting out the repair manual, I saw that zero resistance should
send the gauge to the "full" peg. I briefly grounded it and it did jump
to "Full". For the next year, it worked as it had (around 4 gallons
low). LAst couple of flights, it began reading all over the place, from
less than zero to a few gallons low. Again, I briefly grounded the gauge
and it flew up to zero. But this time, if remained flaky and is reading
all over the place.

By switching the sending units to the opposite gauges, the problem
appears to indeed be with the right sending unit (or the wire from the
terminal block to the sending unit). Checking the blade connector at the
wing did not have any effect.

I cannot remember if there was enough of a hole to get at the wire on
the sending unit when you removed the inspection panel at the right
landing gear. My hope is that the wire has worked loose at the sending
unit terminal. I seem to recall JUST being able to touch the terminal if
I put my arm in it up to the elbow (and it was NOT easy).

Anyone else have any experience with these critters? Are they supposed
to have 2 rivets holding the resistive element(one at either end)? Can
you get at the terminal without pulling the tank? Are new sending units
available for a reasonable price (maybe $200 or so)?

Thanks for any suggestions. Please restrict any feedback to actual
experience.

Mike