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HOW TO: Revive your fuel gauge sender for $1 FAQ
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Daverham
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PostPosted: Thu Oct 08, 2009 9:05 am    Post subject: Reply with quote

Update!

I finally put 'er all back together last night and promptly went out to get a tank of gas. The sender appears to work as it should.

2 gallons... it moved up a tiny little bit.

5 gallons... it was showing a little under half a tank.

7 gallons... it was about half a tank's worth on the gauge.

I stopped after that - just in case I spring a leak someplace (just re-installed the whole tank, hoses, etc) - I'd rather clean up 7 gallons of spilled gas than 14. I'll top 'er off tonight and report back.

Seems to work - now go fix yours, and spend your other $49+ shipping on something cool like mud flaps.
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onion456
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PostPosted: Thu Oct 08, 2009 10:43 am    Post subject: Reply with quote

the trick is in the vibrator- it sends pulses of voltage, spaced pretty far apart, rather than full on 12v. im sure that tiny wire cant handle much current.

here are some links to fuel gauge info (which i found in other posts)
http://www.nls.net/mp/volks/htm/fuel_ga.htm
http://www.type2.com/library/misc/vwggauge.htm

heres what happens when you are messing around and decide to bypass the vibrator:
Image may have been reduced in size. Click image to view fullscreen.

it was brand new and installed in the tank at the time. Shocked after installing the new sender, my gauge was still erratic, so i was playing around with stuff behind the dash trying to figure out what was going on, guess i applied 12v directly to the sender.

btw great writeup =)
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RatCamper
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PostPosted: Thu Oct 08, 2009 1:36 pm    Post subject: Reply with quote

^^^
Yeowch. Guess I have truly been blessed. The vibrator on my gauge went short circuit many, many years ago. Destroyed the gauge in the process. After my recent hack to add a gauge from a truck it was a pleasant surprise to find the sender is still fine.

What did I do about the vibrator? Well... umm...

You see there are two types of units. One is the bimetal vibrator. The other contains a zener and a small lightbulb. The zener for voltage stabilisation and the bulb for current limiting.
I discovered the gauge couldn't care less what voltage was going to it as the sender is working off the same circuit, and the level is determined by the level the gauge returns between the input voltage and the earth.
So currently it's patched in with a parking light bulb and holder I found in the glovebox. I'll replace it with something smaller when I find such a thing.

If anyone has the zener type, could they please find the zener breakdown voltage for me? I couldn't find mention of what it is anywhere.

Awesome project by the way.
Wire that won't solder can usually be soldered by putting a loop in it and 'casting' it into place using solder so the loop is encased on all sides.
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Daverham
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PostPosted: Thu Oct 08, 2009 8:59 pm    Post subject: Reply with quote

Quote:
the gauge couldn't care less what voltage was going to it as the sender is working off the same circuit, and the level is determined by the level the gauge returns between the input voltage and the earth.


Are you saying that it doesn't matter what the resistance is on the sender, for example a 100 or 180 Ohm coil would work just as well as the 70 ohm (per original) coil? This would make sense with a voltage divider network circuit, but the "other" end of the resistor coil isn't grounded, it's just floating, so that doesn't seem like it applies. But I'd love to hear otherwise if you know something that I'm not thinking of. I'm not an electrical engineer... just wanted to be one for a few years!

FYI, I filled up my tank tonight and the gauge is working famously, empty to full - perfect!
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barefootwestie
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PostPosted: Fri Oct 09, 2009 9:05 am    Post subject: Reply with quote

Not sure how I missed this on the first posting, but just found it. Will be bookmarking in case I need for the future. Thnks
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GusC2it
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PostPosted: Fri Oct 09, 2009 9:27 am    Post subject: Reply with quote

FYI, The vibrator has a long history in Automotive electronics.
Many younger guys grew up with solid state radios in their cars. before that, Car radios, like home radios, had tubes. Tubes require high voltage, so in all home tube radios you will find a large transformer that steps up the voltage from 110v. to many hundreds.
In a car radio, the problem was worse because they only had 6v, or 12v to work with. Further, transformers can't work with smooth direct current like from a battery.
The answer was, a vibrator, which pulsed the DC. Transformers can work on pulsed DC! In any old car radio, you will find a transformer and next to it, a large Aluminium can which is the vibrator.
BTW, an ing. coil is a transformer, and the only reason it works, is that the points pulse the smooth current, like a vibrator.
That's my vibrator story. Cool Laughing
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twinfalls
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PostPosted: Tue Oct 20, 2009 11:10 am    Post subject: Reply with quote

My original sender failed a year ago. I replaced it with an aftermarket made in Mexico.
With the new sender the gauge tells 3/4 on a full tank.

I kept the old parts, because I have in mind to replace the broken wire as shown here.
To st the winding, I was thinking using varnish rather than epoxy.

Great thread.
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Chazbot
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PostPosted: Tue Oct 20, 2009 7:02 pm    Post subject: Reply with quote

Very nice post on the sender repair. I have a 70 westy that may need a gauge but I'm torn about whether to cut the hole or dig for it. Any votes on the matter?

I would like to know exactly what brand and type of epoxy he used. Maybe it was in there but I did not recall it. Anyway, the reason that you can run electricity in a tank unit or even a pump is that there is not enough air to ignite the fuel with all the vapors. Just too rich of a mixture and fuel burns rather than exploding like the hydrogen gas emitted by a lead acid battery.

Funny story, I once saw a german service manual translated to England English where they wanted you to remove the fuel sending unit and inspect the inside of the tank using a "Torch"! Yeah kinda scary but in England it means flashlight. Just gotta be careful bringing those instructions to the states eh?
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Daverham
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PostPosted: Wed Oct 21, 2009 7:56 am    Post subject: Reply with quote

Quote:
I'm torn about whether to cut the hole or dig for it. Any votes on the matter?


Oh boy, here it comes!! Shocked

Here's all the votes you could ever want and then some:

http://www.thesamba.com/vw/forum/viewtopic.php?t=382002

Please don't flood this how-to thread with more of the same. I'm also considering fixing these senders for people, for like $25 or something. If anyone is interested, PM me. I'll put up an ad in the proper place. Obviously I have already shared ho to do it, but if you aren't brave, or just don't want to bother, I'll take a stab at it.

The epoxy was some kind of 2-part epoxy in the red and black tubes. Probably JB Weld - the clear stuff, not the gray, putty kind. Maybe a different brand with similar tubes.
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made_in_nz
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PostPosted: Tue Mar 23, 2010 11:47 am    Post subject: Reply with quote

Hi Daverham - great tutorial. I just took my sender apart and it looks as fried as yours did. I'd like to fix it myself if i can find the right NiChrome wire.
Just wondering how your sender is holding up - have you had any problems with it since?
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SGKent Premium Member
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PostPosted: Tue Mar 23, 2010 12:48 pm    Post subject: Reply with quote

if it hasn't been said - early bays have a different kind of sender.
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ts39136
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PostPosted: Thu Apr 22, 2010 6:28 pm    Post subject: Reply with quote

Thanks for that post. I'm converting to subaru using subaru guages and was wondering what to do. I should be able to build the stock sender to subaru specs.

THANKS AGAIN!!
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made_in_nz
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PostPosted: Thu Apr 22, 2010 11:37 pm    Post subject: Reply with quote

I've fixed my sending unit - when I tested it with a multimeter the resistance did jump around a bit but in general it was correct. To be sure I attached it to the bus and watched the fuel guage as my wife moved the float slowly up and down and it looked good.
Yesterday I filled up for the first time since i put the tank and engine back in and the guage is showing full like it should.
I do suspect i may have a bit too much resistance at the lower range (too many coils) but at worst this will just mean that i have more gas in the tank than i think i have.
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mla4est
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PostPosted: Mon Jun 14, 2010 9:11 pm    Post subject: Great Post Helped me tons Reply with quote

After ordering several fuel tank senders that were supposed to be for my bus I had 3 senders that would not work for my 1977. Using your post as a guideline I took the wire board out of one of the senders and replaced it into the original part and refurbed it. Now I know how much gas I have
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PostPosted: Tue Jun 15, 2010 9:13 am    Post subject: Reply with quote

fusername wrote:
german magick, duh.

cool stuff!

thats regenbogen hexenmeister to you buddy
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78'bus
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PostPosted: Mon Sep 20, 2010 7:52 am    Post subject: Reply with quote

Great Post Daverham!

I just took my tank off to repair both the tank and the sender of a 78 transporter, to find that the panel that holds the wire in place in my sender is PLASTIC! It's brittle, so I am planning to make an aluminum panel to replace it, I know that there is an inherent solder problem but I can put a steel screw in it and solder the cables... any other ideas?
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mikewire
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PostPosted: Mon Sep 20, 2010 9:12 am    Post subject: Reply with quote

Thanks Daverham! I just ordered 30ft. to fix mine, and I will use this DIY for sure. Great Job.
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78'bus
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PostPosted: Wed Sep 22, 2010 4:32 pm    Post subject: Reply with quote

Looks like nobody has encounter the same plastic issue, so here was my solution... I used a piece of a fiberglass circuit board; after about 36 hrs of field testing looks like the material withstand gas just fine.

here's my design
Image may have been reduced in size. Click image to view fullscreen.


here's mine with VDO original part
Image may have been reduced in size. Click image to view fullscreen.


Will epoxy tomorrow, I will post the outcomes.
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Last edited by 78'bus on Thu Sep 23, 2010 8:07 am; edited 1 time in total
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PicklePickle
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PostPosted: Wed Sep 22, 2010 5:57 pm    Post subject: Reply with quote

You didn't vary the distance between windings toward the "empty" end of the board like the originals seem to have. I wonder if your readings will end up being a bit more bouncy as a result? Please post with what kind of readings you get as you fill and as you drive and the gas is sloshing around in the tank.
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PostPosted: Mon Sep 27, 2010 6:13 pm    Post subject: Reply with quote

I'd just like to say what a brilliant 'How - 2'. great idea to fix an original part.quality repair as well, no bodging at all and also the layout,good photos & explanation is excellent - Thank you!!
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