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busdaddy Wed Jun 28, 2017 12:13 pm

telford dorr wrote: Looks to me that they ran the wire through the rivet - must have drilled a hole through it. See the wire behind the sender?.
Ahh yes, now that the pic has grown I can see that, wow, odd way to do it.

I've had a couple develop a loose rivet after soldering the terminal onto each end, the plastic melts a bit. I've fixed it by resetting the rivet, but that gets real exciting working in close proximity to that fine wire. It might be safer to run another wire from the rivet end of the fine wire out through another hole in the cap and connecting the sender wire externally.

Dogo Thu Jun 29, 2017 1:13 pm

telford dorr wrote: Dogo wrote: My sender was reading about 3/4 full when in fact it was full.
Yup - that's the typical sender failure mode symptom.

Quote: Took it apart all seems alright, but I now am trying to measure resistance and I get no reading. Wondering if I'm doing it wrong.
Red lead on rivet, black lead on top cast plate.
That's correct.

Quote: Am I setting my meter wrong? Bad meter? Bad sender?
Meter is correct (200 ohm range). Touch the meter leads together. It should read (near) zero.

The sender is likely corroded. The corrosion happens between the brass spring plate and the aluminum case. You can't see it, but you can measure it. Measure from the top plate to the solder joint where the resistance wire connects to the spring plate. It should be zero. If not, you need to add a ground wire.

The other place corrosion will get you is in the rivet which connects the external wire terminal with the resistance wire. Measure from the terminal to the (other) solder joint where the wire connects to the tab under the rivet head. Again, it should read zero. If not, buff and solder both ends of the rivet.

I've never seen the resistance wire itself fail (except when physically broken).


On both those locations I get "zero" as in the display does not even move and reads "1 . "
I also measured against the external wire terminal and the top case, and also get no readings, which, from my understanding should read up to 80, depending on the position of the float; correct?


Dogo Thu Jun 29, 2017 2:49 pm

Getting empty and float half way readings when testing at these locations




telford dorr Thu Jun 29, 2017 2:54 pm

Dogo wrote: On both those locations I get "zero" as in the display does not even move and reads "1 . "
On a digital meter, the display in the pic (above), the reading with a "1" in the leftmost column, means "infinity", or an open circuit. If you short the probes together, the meter should read zero. If it doesn't then one of the probes is bad.

Quote: I also measured against the external wire terminal and the top case, and also get no readings, which, from my understanding should read up to 80, depending on the position of the float; correct?
The sender should read around 80 ohms with the float in the "empty" position.

There are four connections in a fuel sender which you can measure between with your meter:

1) From the lid to the brass spring strip where the resistance wire connects. This should read zero ohms.

2) From the spring strip where the resistance wire connects to the other end of the resistance wire where it connects to the solder lug at the rivet. This should read around 80 ohms with the float in the "empty" position to around 8 ohms with the float in the "full" position.

3) From the solder joint at the rivet to the terminal on the sender lid. This should read zero ohms.

As all of these resistances are in series, if you add up all of these readings, then you should get around 80 ohms from the lid to the terminal on the lid with the float in the "empty" position.

Tcash Thu Jun 29, 2017 3:48 pm

To link to this post
Code: [url=https://www.thesamba.com/vw/forum/viewtopic.php?p=8486645#8486645]Fuel sender testing T2a[/url]

This reading means there is no connection, infinity, null, open circuit, no bueno.
Further testing will be required.



After you put the two test leads together and zero your meter.
This is what you want to see.



A good fuel sender should have these readings.




Let the testing begin. If you do not see 00.0 in between any of these probe points. You have an open or bad connection. Clean, solder, re-set the rivet as previously posted.








telford dorr Thu Jun 29, 2017 7:35 pm

Info note, on meters in general: most meters are pretty inaccurate at reading resistance below about 10 ohms, as there are too many connections between the meter internals and the resistance being measured. These include where the probes plug into the meter and the probe tips themselves, which get dirty and oxidized. You can compensate for this a little by taking a reading with the probes touching. This represents extra series resistance in the meter, and should be subtracted from a reading taken across an unknown resistance. Even so, measuring really low resistances, like across the trannie ground strap, is pretty much hopeless, and other measurement techniques must be used.

Tcash Fri Jun 30, 2017 9:06 am

telford dorr wrote: Tcash wrote: Telford please review and add and edit as you see necessary.
Thank you
Tcash
I don't have direct edit authority, so I'll just pass along changes.

Edited two pix. Take a look.
Thank you
Tcash

dasdachshund Fri Jun 30, 2017 9:56 am

This is a great thread, Telford.
Thanks. =D>

-dasdachshund

telford dorr Fri Jun 30, 2017 11:13 am

Tcash wrote: Edited two pix. Take a look.
Yup - that'll work.

Ry-dog Sat Jul 08, 2017 6:30 pm

Thanks for the write up. I just finished the procedure and all tested well with the Ohm meter. Though I am not getting 0.00, I do get 0.4 and that's the best reading I get when I put the probes together. Resistance readings were between 77-83 ohms when empty and 3.1 ohms when full. Mine was from a 70 Westy and had the typical 3/4 reading when full. Soldered the tin wire and the rivet, but not the spade on top.

Question regarding the penetration using this method. I did use the Loctite 242 at the bolt threads and nut, but do I still need to use a fuel resistant sealer to prevent leakage if I overfill the tank some?

busdaddy Sat Jul 08, 2017 6:37 pm

Yes, the hole the wire passes through has to be sealed, JB weld works well for that.
The .04 OHM is an error in your meter (poor leads, internal issues, etc...) , add that figure to whatever you read to find true OHM's, you should do that every time you fire up the meter anyways.

telford dorr Sat Jul 08, 2017 8:35 pm

Ry-dog wrote: Question regarding the penetration using this method. I did use the Loctite 242 at the bolt threads and nut, but do I still need to use a fuel resistant sealer to prevent leakage if I overfill the tank some?
If you used the screw method to ground the brass spring, and the ground wire does not penetrate the lid (as others have done), then Loctite should do the job. That's all I used on mine, and I have no fuel seepage.

On the other hand, a blob of fuel-proof sealer on the nut certainly won't hurt...

Ry-dog Sun Jul 09, 2017 10:09 am

Ok. Sounds good. I used the screw method to ground the spring and no penetration with wires, just the machine screw. I may go ahead and blob a fuel resistant sealer for good measure.

Thanks for the responses.

CerveloMikey Wed Nov 15, 2017 10:01 pm

Anyone want to take a stab at this early Ghia sender? It is not working and should read from 8-80 ohms. I took the bottom cover off and exposed the float and fine wires. The tube will not separate from the cover. I think I need to remove the rivets to get it apart. I would like to keep it because of the date stamp and I havenít had good luck with the repops.






busdaddy Wed Nov 15, 2017 10:33 pm

Interesting, it does seem the tube is somehow attached with those rivets, I guess my next step would be to drill them out and see what's beneath.

wcfvw69 Thu Nov 16, 2017 8:21 am

Just a stab in the dark here on that sender. Does the tube need to be twisted to unlock it to slide down? It would seem odd that the constructed it in a way that the rivets would have to be removed to get the tube off.

TDCTDI Thu Nov 16, 2017 8:26 am

wcfvw69 wrote: Just a stab in the dark here on that sender. Does the tube need to be twisted to unlock it to slide down? It would seem odd that the constructed it in a way that the rivets would have to be removed to get the tube off.
The tube is held on by the 7 or 8mm nut at the bottom only, once it's removed, the tube slides right off.

CerveloMikey Thu Nov 16, 2017 8:40 am

After reading this thread and seeing how easy the bus senders came apart I thought the same thing. I twisted and wiggled it and nothing. As you can see, the bottom plate is removed and there is nothing holding the tube at the bottom. My guess is the tube has a flange and the flange is trapped between the top cover and the ring held by the rivets. This sender is 60 years old! VDO probably changed the design to speed up production.

busdaddy Thu Nov 16, 2017 8:44 am

TDCTDI wrote: wcfvw69 wrote: Just a stab in the dark here on that sender. Does the tube need to be twisted to unlock it to slide down? It would seem odd that the constructed it in a way that the rivets would have to be removed to get the tube off.
The tube is held on by the 7 or 8mm nut at the bottom only, once it's removed, the tube slides right off.
Well the aluminum tubes do, but that tube looks like bakelite, maybe it's flanged at the top?
From fear of cracking something I'd drill the rivets and dissect it carefully, copper rivets are available at equine supply stores and likely marine stores too, it looks corroded enough that it could likely use a cleaning between that seam anyways.

TDCTDI Thu Nov 16, 2017 8:56 am

Gotcha, I just responded to the last post & didn't back up to see the different version. :oops:



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