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HOW TO: Revive your fuel gauge sender for $1
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Daverham
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PostPosted: Tue Oct 06, 2009 10:35 am    Post subject: HOW TO: Revive your fuel gauge sender for $1 Reply with quote

I'm assuming that if you are reading this, you already have your fuel sender out or know how to get it out. There are plenty of threads about that. It's easy to do the cut-the-hole option with a sawzall (break the blade off short so you don't hammer the fuel tank below). Once you get the bugger out, you can get a new one at The Bus Depot for $50 (http://www.busdepot.com/details.jsp?partnumber=211919051A). Not a bad price. But it's more fun to fix your own... for $1!


1 - Here's the dead sender. Pry up these six tabs and the whole thing comes apart easily.
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2 - Like this.
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3 - There's yer trouble! Worn-out and broken resistive wires from 30 years of filling and emptying the tank.
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4 - It took me a couple tries to figure out the best way to do this. Position your pliers as such and bend up the 4 tabs to free the resistor board from the housing. Be gentle, they can easily go too far, and you'll need room on the other side to get a screwdriver in there and pry them back when you're done, so don't push them all the way to the housing.
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5 - Unwind the old wire.
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6 - Cut off the old wire at the terminal post.
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7- New 36 AWG Nickel Chromium (NiChrome) wire purchased from Jacobs Online (http://jacobs-online.biz/nichrome_wire.htm). I got 10 feet for $2 and used less than half of it (thus the $1 per-sender price tag). Easy payment with PayPal, and they shipped it very fast. This isn't just any 36 gauge wire. It is resistive. If you try this with copper wire you get a big FAIL for the day.
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8 - Measure off 70 Ohms worth of new wire with your meter, then add an extra inch-and-half or so, so you can wrap off the "dead" end of the wire securely. Mine came to about 3 feet - that's just a ball park. I didn't measure the length.
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9 - The terminal post is brass. Clean it off so your solder will stick, and then solder the end of your new wire right on there. At this point I also de-soldered the other end of the blue wire because it's easier to do the next step (wrapping) when it's not connected to the whole unit. Update: They say this wire doesn't stick to solder, so maybe loop it around that blue wire or the terminal post a couple times before soldering, so it can't pull out (not that there will be any pulling).
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10 - Wrap the new wire around the board. This is much easier using a bench vise. I Tried to stay in the grooves left by the old wire, but my 70 Ohm wire was a little shorter then theirs (maybe I'll try 32AWG next time). You can see how the windings get progressively tighter toward the "dead" end of the wire. This is probably to compensate for the change in movement as the float moves along it's arc, so try your best to duplicate that. Don't let the windings touch, or you're wasting your time. Give a little space in between them. It might be a good idea to paint your wire before you do this, then you could get them tighter without any short circuits... as long as you use fuel-proof paint. I opted for leaving a space in between. When you get to the end, use that extra inch of wire to wrap the end off around that little tab. One thought: You can see little kinks in the wire from where it was wrapped around that little plastic card. Next time, I'd rather get wire from a roll so there won't be any kinks.
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11 - Re-install the resistor board by bending the metal tabs back in place with a small screw driver. Don't forget to re-solder the other end of the wire.
Image may have been reduced in size. Click image to view fullscreen.


12 - Apply 2-part epoxy to the resistor wire. 2-part epoxy is fuel-resistant. Spread it as thinly as possibly. You want the wires to stay in place, but you don't want to cover the tops of them, or they will be insulated from the sliding contact point. I tried this without the epoxy and the wires moved around - no good. They need to be glued down.
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13 - Gently scrape the epoxy off the contact surface of the wires. I scraped it once when the epoxy was wet, and again after it had dried. Then hit it very gently with some 600 grit sandpaper or steel wool, just to ensure there is no epoxy on top and the windings are smooth.
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14 - Before putting it all back together, make sure this little brass pivot is clean. That's how the sliding contact point connects to ground. Mine was covered in crusty corrosion. At this stage you might want to give that spring a little stretch too, just to revive it. Mine was weak and compressed.
Image may have been reduced in size. Click image to view fullscreen.

15 - After you put it all back together... test it with a meter. 0-5 Ohms when the tank is full. Perfect (meter reads higher because the float arm moved just as I took the photo). This whole project would have been easier with a meter that has alligator clip leads, by the way. Especially when taking photos.
Image may have been reduced in size. Click image to view fullscreen.

16 - Half-full... Meter reading about 30 Ohms. Looks good.
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17 - Empty tank. Meter reads about 70 Ohms. Rock and roll. Now you can adjust where the float stops by bending the metal tabs that are hanging off the bottom.
Image may have been reduced in size. Click image to view fullscreen.

Results: You can see by the meter test, it works! The movement is smooth and there are no dead spots. I get progressive readings all the way across the movement in increments of about 2-3 Ohms. This whole process took about 40 minutes, including making it up as I go and stopping to take a lot of photos. I bet you could do it in 20.

I'll update you again once I get it in the bus and do a "real world" test, but I'm pretty sure this covers it.

Here's a link to my FIX YOUR FUEL TANK thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=378770

All these edits you see are just because I keep finding typos or feel the need to clarify something.
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Last edited by Daverham on Tue Oct 06, 2009 3:37 pm; edited 12 times in total
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RocketRod
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PostPosted: Tue Oct 06, 2009 10:40 am    Post subject: Reply with quote

Slick! What good timing for me as mine needs this and I was regretting spending the money. Thanks for sharing and the pics!
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73kombi
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PostPosted: Tue Oct 06, 2009 10:50 am    Post subject: Reply with quote

Very nice tutorial...my gauge is still working, but takes a minute or two to go from empty to full. (bumpy roads help) Wink But next time the engine is out, I'm going into the firewall and fixing it.

peace
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Newton
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PostPosted: Tue Oct 06, 2009 11:05 am    Post subject: Reply with quote

Thanks for putting this together, Daverham. All those pics are really great and I can't wait to try this myself. I hate driving around without a working fuel gauge.
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PostPosted: Tue Oct 06, 2009 11:51 am    Post subject: Reply with quote

wow, freakin nifty! i have an old one i never tossed, glad i saved it now!
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patayres
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PostPosted: Tue Oct 06, 2009 12:08 pm    Post subject: Reply with quote

Excellent tutorial. My gauge shows 3/4 with a full tank & I've been contemplating a replacement sender. Now I'll just fix what I've already got.
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Daverham
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PostPosted: Tue Oct 06, 2009 12:13 pm    Post subject: Reply with quote

I'm stoked that people are into this! Please post some pics or just state your results when you get into it. I'd love hear how it goes for other people.
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PostPosted: Tue Oct 06, 2009 1:16 pm    Post subject: Reply with quote

Nice post ! Applause

I actually tried to rewind mine a few years ago and it didn't work. I used a single strand from some speaker wire, but I see now what to use next time.

Thanks!
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PostPosted: Tue Oct 06, 2009 1:20 pm    Post subject: Reply with quote

Sweetness! However it'll be awhile before that far into the belly o' the beast.
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peaceful warrior
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PostPosted: Tue Oct 06, 2009 1:24 pm    Post subject: Reply with quote

Great post Daverham!
BTW, if you ever do this using a roll of wire, make sure you put the spool on a spool holder otherwise the wire will still kink.
Nevertheless, great job and thank you for sharing it with us! Very Happy Wink
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PostPosted: Tue Oct 06, 2009 2:32 pm    Post subject: Reply with quote

Eureka! Too bad i just spent 50 on a new one. Didn't know where to buy the wire! But, I saved the old one! Cool
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PostPosted: Tue Oct 06, 2009 2:36 pm    Post subject: Re: HOW TO: Revive your fuel gauge sender for $1 Reply with quote

Great write up. We use the same type of wire but with higher resistance for rebuilding smoke units on old toy trains.

A few notes - Soldier will NOT stick to the resistance wire. You should make two turns through the soldier eyelet so it won't pull out.

Daverham wrote:
One thought: You can see little kinks in the wire from where it was wrapped around that little plastic card. Next time, I'd rather get wire from a roll so there won't be any kinks.


Here's what I do when working with wire off a card or a roll. Clamp one end in a vise, then pull on the wire gently. The kinks or twists will be pulled out. Do this before you cut the required resistance as pulling the wire will make it slightly longer. This works on any type of bare wire.
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PostPosted: Tue Oct 06, 2009 3:24 pm    Post subject: Reply with quote

Good tip about the solder not sticking. The wire has about 4mm to go from the solder to where it is wrapped/epoxied to the board, with no tension on it of any kind, so I'm not really worried about any pulling. But I would certainly take that good tip into consideration when working with the stuff. I just edited the OP to reflect this tip. Thanks.

I guess I should also clarify that I don't guarantee that this will really work in the gas tank, or that it will be accurate (don't blame me if you run out of gas!) or stand the test of time. I don't really know yet! I'm just sort of experimenting here, and sharing how I did it. I imagine this is a good launching point for somebody who maybe didn't know where to start. There will probably be better ideas and refinements as we all go forward. I hope so.

The next phase it to watch the gauge as I'm filling the tank for the first time and try to assess how well-calibrated this thing is.
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PostPosted: Tue Oct 06, 2009 6:35 pm    Post subject: Reply with quote

AAHHH!!!

I threw away about 25 bad senders not too long ago!!!!!

Thanks for your effort and pics. Now we know.
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PostPosted: Tue Oct 06, 2009 7:35 pm    Post subject: Reply with quote

well done! too bad I just bought one brand new one on ebay for 35. I definitely would go your route next time, just for fun.
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PostPosted: Wed Oct 07, 2009 5:24 am    Post subject: Reply with quote

This could be the solution to my problem of the wandering needle on my fuel guage. One minute she is half full, next minute she is empty, then she is 3/4 full.

I love the idea of renovating the old one rather than sticking a new one in.

Good job mate.
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PostPosted: Wed Oct 07, 2009 7:55 am    Post subject: Reply with quote

Quote:
One minute she is half full, next minute she is empty, then she is 3/4 full.


That's exactly what mine was doing.
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PostPosted: Wed Oct 07, 2009 8:07 am    Post subject: Reply with quote

I'm going to ask because I don't know and hopefully someone does. If the sending unit has voltage going to it and there appears to be some type of arcing going on at the board and wires, then why doesn't it lite the tank off? I could understand when it is submerged but that is the rare case I think.
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PostPosted: Wed Oct 07, 2009 8:16 am    Post subject: Reply with quote

That's a great question. I thought about it myself, and my GUESS is that the system is at such low voltage that there is no chance of a spark. 0-70 Ohms is a VERY low range of resistance. Most resistors you commonly see used in electrical circuits range from 500 - 5,000 Ohms and beyond. So I'm guessing that because the resistive range is so low, that's a good sign that the gauge itself operates at a super low voltage range, which could never spark. It takes quite a bit of voltage to send an arc across open air, or in the case of motor brushes, a lot of current. In the fuel sender you have low values for both voltage and current... that's my theory, anyone know the REAL answer?
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PostPosted: Wed Oct 07, 2009 8:49 am    Post subject: Reply with quote

german magick, duh.

anyways super cool write up. I don't know exactly what the wiper arm looksl ike, but odds are if youcan convince the wire to sit fairly flat on the board on the wiper side i would be best, to avoid the wiper pulling the strands and fatiguing them should the epoxy fail to do its job. A quick spray with a can of varnis would avoid any shorts later, should the wires still move, and 2 seconds w/ emery cloth should reove the varnish where the wiper will ride.

cool stuff!
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