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Wed Dec 23, 2009 5:56 pm

Ok...a little confusion here for me. I placed my VR in the same location as the old vibrator but yours is in a different spot. My current set up:
-> +12V -> gauge -> 10V-VR -> tank sender -> ground

With my rheostat:
-> +12V -> gauge -> 10V-VR -> rheostat -> tank sender -> ground

Anyway...why did you put it in it's location where you did? I figure that since the VR replaces the stock vibrator it would simple be a swap of components (basically speaking) since it's doing the same thing (right?).

I'm not an electronics person so I need expert guidance here.

<edit>
I set mine up, VR and additional resistance, to mimic the stock system. I added the rheostat after the VR and before the tank sender because the tank sender is a rheostat (variable resistance) so I simply made the sender 'more resistant', sort of speak.

I just measured my rheostat and it's at 19.3 ohms. I need to fill up to see where the needle lands. I removed the rheostat and the needle moved almost a full 1/4-tank distance towards the full mark so it's definitely needed.

Wed Dec 23, 2009 8:55 pm

Unless the gauge has an internal connection to ground that I don't know about, the order of components in series after the VR makes no difference, electrically. In practice, you're stuck with one end of the tank sender being grounded, but the resistor and gauge can be wired in either order.
Between varying the output voltage of the VR and the value of the series resistor, you should be able to calibrate the gauge accurately at two locations (generally, empty and full).
I would think that the series resistor would mostly affect the span (how far the gauge moves between 'full' and 'empty'), and the voltage from the VR would mostly affect zero (where the gauge points when the tank is empty.) These adjustments will interact with each other, so experimentation is required.

Thu Dec 24, 2009 6:34 pm

Filled the tank and the needle went about 1mm past the FULL mark so I tweaked the rheostat a smidgen to drop the needle. Got home and read it w/the my ohm meter and 20-ohms on the nose 8) So my slightly educated guess is that when truly empty the needle will be on or just below the left white border of the Reserve (red) zone.

I'm calling it good. So next shopping trip is to get a 20-ohm resistor, solder it in place and call her DONE (after removing the rheostat, of course).

Merry Christmas y'all! :vw:

Sat Dec 26, 2009 12:15 am

So how can you tell if its the thingees under the dash that are bad -- sorry -- clueless to anything you all just said --- or the sending unit in the tank?

In Awe, TH

Sat Dec 26, 2009 11:27 am

Once you've confirmed that the gauge works (needle goes to full) and the sender works (normally requires replacing with a new unit) the last item left, aside from a power check and wiring, is the device that meters the electricity about the gauge. That would be the rectangular can with two wires connected to it that's screwed to the back of the fuel gauge. That's the item we're discussing.

Sat Dec 26, 2009 3:44 pm

What type of setup are in the earlier vehicles?

My 68 does something similar with the gauge never reading full.

Sat Dec 26, 2009 4:26 pm

david_594 wrote: What type of setup are in the earlier vehicles?

My 68 does something similar with the gauge never reading full.

Who cares as long as empty is accurate? :P

The 68-mid 73 system uses an internal regulator in the instrument, try grounding the wire that goes to the sender, if you show a full tank the sender has issues (likely sticking float), if it's still not full it's the gauge in the dash.

Sat Dec 26, 2009 4:59 pm

Air_Cooled_Nut wrote: Once you've confirmed that the gauge works (needle goes to full) and the sender works (normally requires replacing with a new unit) the last item left, aside from a power check and wiring, is the device that meters the electricity about the gauge. That would be the rectangular can with two wires connected to it that's screwed to the back of the fuel gauge. That's the item we're discussing.

Thanks, I'll check that out.

TH

Mon Dec 28, 2009 12:11 pm

Air_Cooled_Nut wrote: Ok...a little confusion here for me. I placed my VR in the same location as the old vibrator but yours is in a different spot. My current set up:
-> +12V -> gauge -> 10V-VR -> tank sender -> ground

Someone [expert] chime in and tell me if this is wrong [for 76-79] :), but I believe the Vibrator/Stabilizer receives 12v then feeds that to the gauge, and averages/limits the power sent to the gauge. Therefore the 10VR should sit between 12v-power and gauge. I believe you are sending 12v to your gauge and then regulating it to 10V after the gauge. :?:

My understanding of the stock setup is:
->12v power ->Voltage-Stabilizer/Vibrator ->Gauge -> tank sender ->Ground.
therefore [my setup using the VR and POT]
-> +12V -> 10V-VR -> gauge ->POT/rheostat -> tank sender -> ground

The POT/rheostat could sit anywhere after the VR and induce additional resistance. I put mine between the gauge and tank sender because it was easy to get to.

It sounds like your gauge is getting a full 12v fed to it[therefore the VR is doing nada]. Which may explain why the needle was reading excessively high. Mine too was high, but the POT helped trim it back.
Whatever works though, I know I'm happy with a realistic FULL reading 8)

Mon Dec 28, 2009 3:34 pm

$h!t #-o I looked at my Bentley and you're right. I got mine to work, though. So back under the dash I go to rewire and retest. ](*,)

Mon Dec 28, 2009 5:15 pm

Hooked up correctly now. Rheostat set at 20-ohms and the needle is about a millimeter lower so it looks like it may take less resistance to tune it. Anyway, it's getting cold and dark out so hopefully I'll finish tomorrow -- gonna pull the sender and make adjustments.

As for a resistor, what wattage should I get? I've seen 1/8W, 1/4W, 1/2W, and 1W at Radio Shack and I know where I got my VR there are even more types. I did have two, 20-ohm by 1W resistors in series and they got warm...not hot but definitely warm.

Mon Dec 28, 2009 6:01 pm

^^I looked for an inline resistor too, but didn't know the resistance to add early on, and couldn't find any that were rated over 1watt either.
Is your rheostat a linear type? [a slider] I used a Potentiometer [rotary dial type] as a rheostat by using two of it's three connections. The POT is working for me, but I agree a single non-adjustable inline resistance would be optimal.

Mon Dec 28, 2009 6:46 pm

Mine is a rotary/dial type -- the packaging read "rheostat". 25-ohms, 3W @ 20% tolerance.

Huh...20% tolerance would explain why the 20-ohms of resistors I added dropped the needle further than expected! That's pretty crappy. The resistors were 5% (gold band). Sigh.

Mon Dec 28, 2009 6:54 pm

20% tolerance is the range of travel. X ohms on the center of a pot is still X ohms.

examples of tolerance of a 20 - 100 ohm pot.

measured between outside pins 20 - 100 ohms (0%)
measured between outside pins 18 - 120 ohms (20%)

But the wiper will measure exactly in resistance to whatever you have it dialed to between these two limits.

It is like saying we promise there will be between 90 and 110 apples in this apple box of 100 apples when you open it (which is 20% tolerance). But when you actually count them and give a measurement you say "this box has exactly 97 apples." When you measure the resistance on the center wiper it will be the actual ohms it is set to.

Sat Jan 02, 2010 2:19 pm

Had a break in the weather today (no snow, rain, or freezing weather) so I pulled the sender and tweaked my rheostat. To have my needle lay on the first white line (the left-most area) of the red Reserve area it needs 15-ohms. When I move the sending float to the full stop on the sender the gauge needle goes just a millimeter past the 1/1 mark (Full). I find this acceptable because I don't need to know exactly where Full is (I know the tank has fuel in it), just exactly where Empty is (will I make it to the next gas station?) :!:

Next stop this week will be 1-watt or greater resistor(s) to get me 15-ohms of resistance to replace the rheostat.

Sat Jan 02, 2010 6:40 pm

I know it's not solid state, but were you guys aware of this?

http://www2.cip1.com/ProductDetails.asp?ProductCode=VWC%2D113%2D957%2D099

Sat Jan 02, 2010 7:32 pm

saw this on RATWELL so it may be solid state??

Notes:
There are three styles of fuel gauge vibrator. I'm only interested in the last one:

VDO 50/5/1, Bi-metallic adjustable style can that needs to be kept away from hot wires.
VW 113 957 099, Zener style with large base. Zener breaks if you try to service the bulb.
VW 113 957 099A, Zener style but better design so you can service the 5W bulb.

Sat Jan 02, 2010 8:54 pm

magnus0328 wrote: I know it's not solid state, but were you guys aware of this?

http://www2.cip1.com/ProductDetails.asp?ProductCode=VWC%2D113%2D957%2D099
I got what I believe is the same unit from my VW FLAPS. Worthless. My Bus came with the bi-metalic vibrator -- I took mine apart after I determined it didn't work. The thin wire inside burned apart, breaking the circuit.

Also, that cost plus shipping charges would get you 3 complete "shadetree" fixes ;)

Sat Jan 02, 2010 9:10 pm

our 77 bus had one of the late style in it when we bought the bus but the fuel gauge did not work. The gauge wires were burned out which implies that the zener style had cooked it. I think that if this home-made zener can be made to work, it will be more robust and reliable than the factory zener one. I also think that one is better off to have it read just a tad low at full because that means less current is going through the gauge so it will last longer.

Sun Jan 03, 2010 9:19 am

SGKent wrote: ...I think that if this home-made zener can be made to work, it will be more robust and reliable than the factory zener one. I also think that one is better off to have it read just a tad low at full because that means less current is going through the gauge so it will last longer.
If this is what one would prefer then make the resistance 17-ohms.