Home » Public Forums » GMCnet » Sending unit test
| Sending unit test [message #311707] |
Fri, 30 December 2016 20:57  |
Atom Ant
Messages: 170
Registered: October 2016
Location: Austin, TX
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Finally got the time to drop the tanks on the coach! I got the sending units out and tested them. I get a proper 3-93 ohms reading on one. On the other, I cannot get a reading when I put the probe to the positive terminal, but do get a reading if I probe under the plate, where the wire attaches to the terminal on the bottom. The reading isn't 3-93, but 90-ish to 180 ish, so still 90 ohms. Is this a problem? If one were to want to replace the terminal, what would be the best way to do so? I know I there's only the need for one working unit, but if it's not too much trouble, I'd rather have two working senders.
I'll have more questions coming, as I get these tanks cleaned up and re installed.
Thanks everyone.
1976 Palm Beach
Austin, TX
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| Re: Sending unit test [message #311718 is a reply to message #311707] |
Sat, 31 December 2016 08:17  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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It sounds like the rivet which connects the wire and terminal is loose or corroded. Carefully drill it out and replace it with a suitably sized brass bolt, nut, and star washer and it should make constact properly.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Sending unit test [message #311806 is a reply to message #311707] |
Tue, 03 January 2017 23:36 |
Atom Ant
Messages: 170
Registered: October 2016
Location: Austin, TX
Karma: 0
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I decided that if I was going to send them
In for repair, I might as well try to fix them. If I screwed them up, well I'd be sending them
In anyway...
I was getting really inconsistent readings on both senders. They would range correctly, then jump all over the place.
I drilled out the positive post like Johnny mentioned. The grommets were in varied conditions. One split right away, and one cracked but not to the middle. The two on the underside survived.
I removed the pin, and contact strap from the baseplate. Cleaned the strap with a rotary tool brush, used rubber washers and a brass screw and nut and re assembled. Tested again, and more consistent range than before, but would still bounce around on one and was all over the place on the other. Jumping from 10 to 7000 with everything in between.
I decided I was gonna dive in and sink or swim. I bent the tab on the flat side of the housing, then slid the housing off. I figured it would be better to break one tab instead of three. This proved to be a good decision.
Inside I found the potentiometer windings and the contact point both on pretty dirty shape.
I cleaned both with contact cleaner, let dry, then used a trick I found while searching for info on this topic.
Apparently a pencil eraser is a great cleaner to remove the buildup on the contact point. Sure enough, it gets it shiny as a new penny. I cut the eraser off the pencil so I could get it into the inside of the case, and gently cleaned the windings.
on the unit that was acting up, I noticed that the windings were not centered on the board inside that keeps it seperate from the casing. In fact, it was so far off the board, it was actually grounding. I adjusted the board, cleaned and re-assembled the unit.
I did break the tab on one pressing it back down. The other seems okay. I imagine a touch of JB weld will do just fine.
I tested each unit, and am getting a consistent range of 10-100 on both senders with no jumping around.
I took pics, and will edit this post with pics tomorrow when I have access to a computer.
1976 Palm Beach
Austin, TX
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| Re: [GMCnet] Sending unit test [message #311807 is a reply to message #311806] |
Tue, 03 January 2017 23:53 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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Senior Member |
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I remember using pencil erasers to clean up contacts on my afx slot cars as
a kid. Those things were cool.
Sully
77 eleganza 2
Seattle
On Tue, Jan 3, 2017 at 9:36 PM Adam Metzger wrote:
> I decided that if I was going to send them
>
> In for repair, I might as well try to fix them. If I screwed them up, well
> I'd be sending them
>
> In anyway...
>
>
>
> I was getting really inconsistent readings on both senders. They would
> range correctly, then jump all over the place.
>
>
>
> I drilled out the positive post like Johnny mentioned. The grommets were
> in varied conditions. One split right away, and one cracked but not to the
>
> middle. The two on the underside survived.
>
>
>
> I removed the pin, and contact strap from the baseplate. Cleaned the
> strap with a rotary tool brush, used rubber washers and a brass screw and
> nut
>
> and re assembled. Tested again, and more consistent range than before,
> but would still bounce around on one and was all over the place on the
> other.
>
> Jumping from 10 to 7000 with everything in between.
>
>
>
> I decided I was gonna dive in and sink or swim. I bent the tab on the flat
> side of the housing, then slid the housing off. I figured it would be
>
> better to break one tab instead of three. This proved to be a good
> decision.
>
>
>
> Inside I found the potentiometer windings and the contact point both on
> pretty dirty shape.
>
>
>
> I cleaned both with contact cleaner, let dry, then used a trick I found
> while searching for info on this topic.
>
>
>
> Apparently a pencil eraser is a great cleaner to remove the buildup on the
> contact point. Sure enough, it gets it shiny as a new penny. I cut the
>
> eraser off the pencil so I could get it into the inside of the case, and
> gently cleaned the windings.
>
>
>
> on the unit that was acting up, I noticed that the windings were not
> centered on the board inside that keeps it seperate from the casing. In
> fact, it
>
> was so far off the board, it was actually grounding. I adjusted the board,
> cleaned and re-assembled the unit.
>
>
>
> I did break the tab on one pressing it back down. The other seems okay.
> I imagine a touch of JB weld will do just fine.
>
>
>
> I tested each unit, and am getting a consistent range of 10-100 on both
> senders with no jumping around.
>
>
>
> I took pics, and will edit this post with pics tomorrow when I have access
> to a computer.
>
>
>
>
>
>
>
>
>
>
>
> --
>
> 1976 Palm Beach
>
> Austin, TX
>
>
>
> _______________________________________________
>
> GMCnet mailing list
>
> Unsubscribe or Change List Options:
>
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>
>
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] Sending unit test [message #311808 is a reply to message #311806] |
Wed, 04 January 2017 00:02 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Adam,
You've done as I did a couple of times 'way back. The technique works well
but I have one caution: The "rubber washers" you used to insulate the
terminals will most likely not survive the ethanol--laced gasoline for very
long. Then you'll have fuel leaking around the contacts. I encourage you
to find some nylon or other ethanol-resistant washers to replace the rubber
(if they're faucet washers, they almost certainly will not hold up). No
use having to drop the tanks again just for that little problem -- been
there, done that.
Ken H.
On Wed, Jan 4, 2017 at 12:36 AM, Adam Metzger wrote:
> I decided that if I was going to send them
> In for repair, I might as well try to fix them. If I screwed them up, well
> I'd be sending them
> In anyway...
>
...
> Cleaned the strap with a rotary tool brush, used rubber washers and a
> brass screw and nut
> and re assembled....
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Sending unit test [message #311810 is a reply to message #311707] |
Wed, 04 January 2017 00:42 |
Atom Ant
Messages: 170
Registered: October 2016
Location: Austin, TX
Karma: 0
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Hi Ken- the bottom that are on the senders survived. Do you think the washers/insulators on the top of the senders need to be fuel proof too? I can't think of a reason this seal needs to be perfectly air/fuel tight. Thoughts? I got nylon washers and spacers too. I actually just grabbed a bunch of different stuff to see what would work. Thanks for the heads up.
1976 Palm Beach
Austin, TX
[Updated on: Wed, 04 January 2017 00:43] Report message to a moderator |
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| Re: [GMCnet] Sending unit test [message #311817 is a reply to message #311810] |
Wed, 04 January 2017 07:45 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Adam,
I don't think the bottom washers alone will seal the connection. If they
would, why wouldn't steel washers do on top? I DO think the senders need
to be fuel tight -- otherwise they'll leak when the tank's full. I just
don't see any reason to not do the very best possible while at it to avoid
difficult work later.
Ken H.
On Wed, Jan 4, 2017 at 1:42 AM, Adam Metzger wrote:
> Hi Ken- the bottom washers that are on the senders survived. Do you
> think the washers/insulators on the top of the senders need to be fuel proof
> too? I can't think of a reason this deal needs to be perfectly air/fuel
> tight. Thoughts? I got nylon washers and spacers too. I actually just
> grabbed a bunch of different stuff to see what would work. Thanks for the
> heads up.
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Sending unit test [message #311831 is a reply to message #311829] |
Wed, 04 January 2017 12:47 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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Atom Ant wrote on Wed, 04 January 2017 13:10Hi Ken-
I realized that my statement may come across as me seeming lazy instead of actually curious.
I agree, and will find a way to seal it. both of my top rubber isolators are hard, and the bottom washers are soft. I was thinking that maybe it was different material, not necessarily for sealing the hole super tight as much as isolating the contacts. I'll concede to much more experienced minds.
I've been toying with the idea of using a fuel resistant gasket maker, and making gaskets. how hard could it be, right? 
Adam,
If it goes wrong, your have two issues:
Shorting the signal will read full or over.
The possibility of an ark in the fuel environment.....
Do you have a friend that owns a lathe??
Buy him a piece of nylon rod stock. He can make washers/spacers with the step to hold the center.
Or, get a pair of nylon washers and a tiny O-ring to crush between them.
The second is what I did for a repair when I was away from my lathe. Not in my coach fuel tank, and I am going to make the right parts some day.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Sending unit test [message #311832 is a reply to message #311831] |
Wed, 04 January 2017 12:51 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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When I did my in-tank fuel pump installation I was able to find nylon stepped waters and and nylon regular washers in the parts boxes at my local ACE hardware store.
I had to drill out the regular washers to fit over the stepped washers on the outside of the sender.
Much easier than having to have some machined.
Emery Stora
77 Kingsley
Frederick, CO
> On Jan 4, 2017, at 11:47 AM, Matt Colie wrote:
>
> Atom Ant wrote on Wed, 04 January 2017 13:10
>> Hi Ken-
>>
>> I realized that my statement may come across as me seeming lazy instead of actually curious.
>>
>> I agree, and will find a way to seal it. both of my top rubber isolators are hard, and the bottom washers are soft. I was thinking that maybe it
>> was different material, not necessarily for sealing the hole super tight as much as isolating the contacts. I'll concede to much more experienced
>> minds.
>>
>> I've been toying with the idea of using a fuel resistant gasket maker, and making gaskets. how hard could it be, right? :p
>
> Adam,
>
> If it goes wrong, your have two issues:
> Shorting the signal will read full or over.
> The possibility of an ark in the fuel environment.....
>
> Do you have a friend that owns a lathe??
> Buy him a piece of nylon rod stock. He can make washers/spacers with the step to hold the center.
> Or, get a pair of nylon washers and a tiny O-ring to crush between them.
>
> The second is what I did for a repair when I was away from my lathe. Not in my coach fuel tank, and I am going to make the right parts some day.
>
> Matt
>
>
> --
> Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
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| Re: Sending unit test [message #311858 is a reply to message #311707] |
Fri, 06 January 2017 11:22 |
Atom Ant
Messages: 170
Registered: October 2016
Location: Austin, TX
Karma: 0
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Senior Member |
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Ken, can you tell me what you used to seal and isolate the contacts? I'm considering buying a sheet of Viton or Karropak gasket material. A punch to make the washer and a needle through the middle should seal it fine.
The top washer is 1/8 thick. About the same thickness as fuel line. Cutting a piece in a small square would more than cover it, and the concave side down would add some tension, adding to the seal. Why would that not work?
1976 Palm Beach
Austin, TX
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| Re: [GMCnet] Sending unit test [message #311865 is a reply to message #311858] |
Fri, 06 January 2017 14:35 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Adam,
After the failure of my earlier repair, I replaced the entire pickup
assembles with new SS ones fromeBay:
http://www.gmcmhphotos.com/photos/g6842-fuel-tank-sender-replacement.html
So, in view of my failure, I'm reluctant to recommend any particular
repair. :-)
Good luck!
Ken H.
On Fri, Jan 6, 2017 at 12:22 PM, Adam Metzger wrote:
> Ken, can you tell me what you used to seal and isolate the contacts? I'm
> considering buying a sheet of Viton or Karropak gasket material. A punch to
> make the washer and a needle through the middle should seal it fine.
>
> The top washer is 1/8 thick. About the same thickness as fuel line.
> Cutting a piece in a small square would more than cover it, and the concave
> side
> down would add some tension, adding to the seal. Why would that not work?
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Sending unit test [message #311866 is a reply to message #311865] |
Fri, 06 January 2017 14:46 |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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Senior Member |
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Ken:
The best “repair” is a “replace”.
Stainless, too!
Thanks for the tip.
Dolph
DE AD0LF
Wheeling, West Virginia
1977 26’ ex-PalmBeach
1-Ton, Sullybilt Bags, Reaction Arms, 3.70 LSD, Manny Transmission, EV-6010
“The Aluminum and Fiberglass Mistress"
> On Jan 6, 2017, at 3:35 PM, Ken Henderson wrote:
>
> Adam,
>
> After the failure of my earlier repair, I replaced the entire pickup
> assembles with new SS ones fromeBay:
> http://www.gmcmhphotos.com/photos/g6842-fuel-tank-sender-replacement.html
>
> So, in view of my failure, I'm reluctant to recommend any particular
> repair. :-)
>
> Good luck!
>
> Ken H.
>
>
> On Fri, Jan 6, 2017 at 12:22 PM, Adam Metzger wrote:
>
>> Ken, can you tell me what you used to seal and isolate the contacts? I'm
>> considering buying a sheet of Viton or Karropak gasket material. A punch to
>> make the washer and a needle through the middle should seal it fine.
>>
>> The top washer is 1/8 thick. About the same thickness as fuel line.
>> Cutting a piece in a small square would more than cover it, and the concave
>> side
>> down would add some tension, adding to the seal. Why would that not work?
>> --
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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