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Tim Donahoe
Samba Member
Joined: December 08, 2012
Posts: 11740
Location: Redding, CA
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 Posted: Tue Dec 18, 2018 7:57 pm Post subject: Re: Fuel gauge calibration |
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Dwayne, the new-type vibrator I installed about four years ago was purchased at Wolfgang International (it might have been Wolfsburg West). It was more expensive than some of the cheaper models of the new-type vibrators that some vendors sell, and these latter, cheaper models may or may not contain a zenor diode.
Mine definitely has the single hump on the back for the zenor diode.
When I first installed this vibrator, I also installed a new VDO sender that I purchased from Wolfsburg West (these senders are now seemingly unobtainable). The gauge, I reused, and was an OEM one.
I got a nice 1/1 full reading for awhile until, as I have said before, I filled my tank with Shell gas. Now—and since I used that Shell gas about three years ago—my gauge reads 7/8ths full when full. So, except for the 1/8th I lost that day at the Shell station, I just consider my tank full when reading the almost full gauge reading of 7/8ths full. This, I consider to be no big deal
When my gauge just touches the Reserve mark, I have about 2 gallons of fuel left. I always fill up at this mark, by the way, and it’s always consistent. So, I never fear running out of gas. Especially since I am more concerned with consistent accuracy toward the Reserve mark, as compared to the full reading.
I did have a recent problem where the gauge only showed a little past full when I had just filled the tank, but that erroneous reading ended up being due to poor contact at the sender power wire connection. This has been fixed, so I’m back to 7/8ths full after a fill up.
So, I guess parts compatibility has a lot to do with which new-type vibrator you buy. Get the more expensive one with the zenor diode.
I’ll check my receipt folder to see if I can find where I bought it.
Tim
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Tim Donahoe
Samba Member
Joined: December 08, 2012
Posts: 11740
Location: Redding, CA
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| Posted: Tue Dec 18, 2018 10:05 pm Post subject: Re: Fuel gauge calibration |
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Okay, I checked my vast folder of receipts, and I definitely bought the black plastic vibrator with zenor diode in August of 2013 from Wolfgang International.
Tim
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Buggeee
Samba Member
Joined: December 22, 2016
Posts: 4416
Location: Stuck in Ohio
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| Posted: Wed Dec 19, 2018 6:29 am Post subject: Re: Fuel gauge calibration |
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As to question 7B
The vibrator needs to be grounded. So if the gauge and vibrator are out of the speedometer the vibrator won't be grounded. You'll have to make a deliberate ground for the vibrator. It would have been grounded where that little screw holds it to the body of the speedometer. If the vibrator is not grounded, it's being bypassed. I found at one point in my process that when I had the gauge and vibrator out of the speedometer it would read much fuller, in fact it would slam to the full mark but then when I ground the vibrator to the car it wood act the same way that it would in the speedometer. I don't know if that advances the process at all for you but that was my experience.
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1966 Sportsmobile Camper https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0
72 Super Duper http://www.thesamba.com/vw/forum/viewtopic.php?t=672387
(adopted out) 61 Turkis Pile https://www.thesamba.com/vw/forum/viewtopic.php?t=728764
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Blue69Baja
Samba Member
Joined: September 04, 2008
Posts: 1065
Location: Fair Oaks
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| Posted: Wed Dec 19, 2018 10:42 am Post subject: Re: Fuel gauge calibration |
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| Buggeee wrote: |
As to question 7B
The vibrator needs to be grounded. So if the gauge and vibrator are out of the speedometer the vibrator won't be grounded. You'll have to make a deliberate ground for the vibrator. It would have been grounded where that little screw holds it to the body of the speedometer. If the vibrator is not grounded, it's being bypassed. I found at one point in my process that when I had the gauge and vibrator out of the speedometer it would read much fuller, in fact it would slam to the full mark but then when I ground the vibrator to the car it wood act the same way that it would in the speedometer. I don't know if that advances the process at all for you but that was my experience. |
Your findings are correct, thanks for the post.
Both the OEM vibrator and the diode regulator types need that ground tab secured.
The OEM vibrator will fry the gauge heating element wires due to the flow of the current not being interrupted..thus not being regulated.
The Zener will not regulate if that ground tab is not secure and will at some point fry the gauge. The light bulb will glow bright and the case will get quite warm.
My recent purchases of the zener types all have a 5.1 zener inside. 3 of them.
I ordered them from different sources. They are all the same.
Amazon, Ebay and JBUGS.
The 3 gauges I bought are all the same from the 3 different sources too.
33 ohms...
Putting 12vdc direct on the meter is a killer! I would not do it for more than about 2 seconds.
When the ignition switch is turned on the OEM vibrator will put 12vdc to the gauge. Thus the current will flow through the sending unit and gauge.
If the vibrator is not working then this happens:
OEM gauge is about 15 ohms and if the tank is full 10 ohms...
25 ohms and 12vdc is about 1/2 an amp flowing through that 30 ga nichrome wire wound around that bimetal arm in the gauge. It is going to fry!
Jim
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69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original.. |
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Buggeee
Samba Member
Joined: December 22, 2016
Posts: 4416
Location: Stuck in Ohio
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| Posted: Thu Dec 20, 2018 8:00 pm Post subject: Re: Fuel gauge calibration |
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As to question 7D
I would not be messing with the calibration of an OEM gauge. Especially to try to match it to a suspect aftermarket sender. The OEM gauge is the only OG reference point you have at this point. I would instead be attempting a recalibration experiment on a twenty dollar aftermarket gauge that is already goofy anyway. My suspicion is that trying to recalibrate these gauges will be an exercise in frustration but now I'm thinking about trying it on one of the two aftermarket wastes I have sitting on my tool bench.
In looking in the little holes I think the calibration is only going to affect the resting location of the pointer. The length of the arc is not going to be affected by what is available in this gauge. The length of the arc, however, is the problem. It's not arching far enough with the given current (I am electrically illiterate so current may not be the correct word).
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1966 Sportsmobile Camper https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0
72 Super Duper http://www.thesamba.com/vw/forum/viewtopic.php?t=672387
(adopted out) 61 Turkis Pile https://www.thesamba.com/vw/forum/viewtopic.php?t=728764
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Blue69Baja
Samba Member
Joined: September 04, 2008
Posts: 1065
Location: Fair Oaks
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| Posted: Thu Dec 20, 2018 10:34 pm Post subject: Re: Fuel gauge calibration |
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Agree, this exercise is only for the non OEM gauge and regulation to make the gauge work with either the OEM or NON OEM sending units.. BTW, both sending units resistances are very close. 10 and 72 or so ohms.
When the day comes that your OEM Vibrator gives up and your gauge, after market or OEM is still good perhaps we will have a solution for regulation... Again...
OEM gauge is <>15 ohms
Non OEM gauge is <> 33ohms.
The differences reduce the current almost 1/2 when you have a full tank using the NON OEM gauge. The reduced current caused by the increased resistance of the NON OEM gauge will cause it to read really low!
After market Zener regulator is set to <>5.1 vdc.. OK for OEM gauge, but not accurate. But is a POS for aftermarket gauges which needs more current to heat up the Bimetal lever! The current voltage I am working with is 7.2vdc.
Either one lives with the inaccuracies like everyone is talking about or we have an easy solution. A fairly accurate system.
Jim
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69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original.. |
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runamoc 
Samba Member
Joined: June 19, 2006
Posts: 5601
Location: 37.5N 77.1W
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| Posted: Fri Dec 21, 2018 7:55 am Post subject: Re: Fuel gauge calibration |
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| Quote: |
| A fairly accurate system. |
Not sure how you drive your VW but the fuel in my tank is in a constant state of 'sloshing'. When I'm driving my fuel level is more of an 'average' than an actual level.
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Daily driver: '69 Baja owned 44 yrs - Plan B: '81 Rabbit Diesel LS Deluxe - Plan C: '72 Ghia
Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs-
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Blue69Baja
Samba Member
Joined: September 04, 2008
Posts: 1065
Location: Fair Oaks
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| Posted: Fri Dec 21, 2018 10:24 am Post subject: Re: Fuel gauge calibration |
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| runamoc wrote: |
| Quote: |
| A fairly accurate system. |
Not sure how you drive your VW but the fuel in my tank is in a constant state of 'sloshing'. When I'm driving my fuel level is more of an 'average' than an actual level. |
My 69 Baja has a 12 gallon tank... with OEM fuel gauge, vibrator and sending unit. Pretty stable...
My 72 Super before it fried its OEM gauge was stable and with all non OEM gauge stuff it is stable. The stock tank has vertical baffles to reduce the slosh..
A stock OEM gauge is pretty quick to react to sloshing but not to the extent you are describing..hahahaaa.... Interesting though.
Jim
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69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original.. |
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Buggeee
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Joined: December 22, 2016
Posts: 4416
Location: Stuck in Ohio
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Blue69Baja
Samba Member
Joined: September 04, 2008
Posts: 1065
Location: Fair Oaks
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| Posted: Fri Dec 21, 2018 4:41 pm Post subject: Re: Fuel gauge calibration |
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| Buggeee wrote: |
| runamoc wrote: |
| Quote: |
| A fairly accurate system. |
Not sure how you drive your VW but the fuel in my tank is in a constant state of 'sloshing'. When I'm driving my fuel level is more of an 'average' than an actual level. |
I think I read somewhere that the OG vibrator was included to result in an average of the flow through the wires, in order to to slow down potential changes in readings due to sloshing. |
Correct Buggeee. One other thing that I spelled out is the OG vibrator is adjustable. The adjustment increases or decreases the pulsing thus adjusting the DC voltage level. This adjustment compensated for the differences from one gauge to another. If you can imagine the bimetal strip being mfg in bulk.. and along with that the resistance of the nichrome insulated wire that is wound around it. Impossible to be consistent. So the vibrator was adjustable.
The gauge as you know is also adjustable.
I have attempted to dig up some factory documents that would tell us what the process was but I have found no trace.
When the ignition switch is first turned on the current through the vibrator to the gauge is constant. We see an OEM gauge and Vibrator will cause the needle to rise rapidly... That is because the Vibrators bimetal takes a bit to react to the temperature developed by the nichrome wire which is resistive.
Nichrome wire is used in toasters and other things like electric stoves, electric heaters etc.
How bimetal strips work, for those that do not know. As a note the light would be the nichrome wire wrapped around the bimetal strip.
Advance to 7 min to see how it works... Remember I was telling in the video I made that the cycle on and off was about .8 seconds!
Link
Jim
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72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original.. |
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Dwayne1m
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Joined: December 31, 2011
Posts: 3538
Location: Pennsylvania
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| Posted: Fri Dec 21, 2018 6:30 pm Post subject: Re: Fuel gauge calibration |
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| That is a cool video. |
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Dermodad
Samba Member
Joined: January 14, 2010
Posts: 28
Location: Texarkana, TX
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| Posted: Mon Dec 24, 2018 4:17 pm Post subject: Re: Fuel gauge calibration |
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| I am wondering if it is really possible to accurately reproduce the stock gauge function after substituting a solid-state fixed voltage regulator for the stock vibrator? Seems like the bimetallic gauge would really be responsive to current (amps) more than voltage. And although I realized current is proportional to voltage in this simple current, the vibrator/interrupter throws a wrench into the equation. It might be more accurate to match an appropriate fixed current regulator, if such exists. Or maybe that makes no sense at all, since a fixed current might result in a fixed gauge reading. I dunno. Going mad. |
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Blue69Baja
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Joined: September 04, 2008
Posts: 1065
Location: Fair Oaks
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| Posted: Tue Dec 25, 2018 6:01 pm Post subject: Re: Fuel gauge calibration |
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| Dermodad wrote: |
| I am wondering if it is really possible to accurately reproduce the stock gauge function after substituting a solid-state fixed voltage regulator for the stock vibrator? Seems like the bimetallic gauge would really be responsive to current (amps) more than voltage. And although I realized current is proportional to voltage in this simple current, the vibrator/interrupter throws a wrench into the equation. It might be more accurate to match an appropriate fixed current regulator, if such exists. Or maybe that makes no sense at all, since a fixed current might result in a fixed gauge reading. I dunno. Going mad. |
The OEM vibrator voltage is a fixed output. It might vary just a bit. .2vdc at the most when working properly. One can not measure the true DC because the vibrator is pulsing. The OEM vibrator will not work properly on the non OEM gauge which is 33 Ohms.
I currently have 2 non OEM gauges 33 ohms working very well with a Zener/bulb regulator with a 7.5vdc Zener! A little adjustment to the gauge is needed if one wants accuracy. The adjustment is not the accessible one, it the one that is hidden behind the plastic. Full swing is obtained. Been burning in for a couple of days at full tank.. Which is max current for the bimetal wire coil.
I also had them running an adjustable step down buck regulator.. Works beautiful with that too.
My current thoughts are that the Zener regulation is a preference... Simple.
More to come.
Jim
_________________
69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original.. |
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Dermodad
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Joined: January 14, 2010
Posts: 28
Location: Texarkana, TX
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| Posted: Fri Dec 28, 2018 9:14 pm Post subject: Re: Fuel gauge calibration |
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I started this thread, and may be more confused than ever. My stock gauge and vibrator "worked" fine with a full tank, but never fell below 1/4 even when bone dry (out of gas!).
Stock sending unit did fail to register high ohms at empty position.
New JBugs cheap sending unit showed 1/1 when full; but gauge dropped precipitously after 1 gallon consumed (gauge showed 1/2 or less). No difference with new or original vibrator.
Latest bizarre finding is that when the new sending unit is out of the tank, it produces proper Ohms readings AND when wired up (but out of tank) it produces full range appropriately on the gauge! Almost like there is some sort of mechanical interference with the travel of the floats when installed.
I do have an adjustable Buck regulator to play with; but I cannot fathom why the thing works out of the tank, but not in the tank.
Mine is a 72 Super Beetle. The sender has 2 arms and 2 floats. The short arm directly controls the rheostat. The long arm indirectly controls the rheostat by contacting the short arm.
I see where RockAuto offers a VDO "adjustable" sending unit. Anybody know what is adjustable about it????? |
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Dwayne1m
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Joined: December 31, 2011
Posts: 3538
Location: Pennsylvania
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| Posted: Fri Dec 28, 2018 9:25 pm Post subject: Re: Fuel gauge calibration |
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| Dermodad wrote: |
I see where RockAuto offers a VDO "adjustable" sending unit. Anybody know what is adjustable about it????? |
I just bought one of those VDO adjustable senders from RockAuto. They claim it will work for a 78 Super. IT WILL NOT!!! I had to send it back. What a PITA to send something back to RockAuto. The entire unit is adjustable, the "stem" or whatever the main part is called, and the arm for the float is adjustable. Why it won't work for my 78SB is that it BOLTS to the tank. It's not the twist in style, and there is only 1 arm with a float. It might work for older cars with that style of sender but I can't say if the bolt pattern will match. |
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Dermodad
Samba Member
Joined: January 14, 2010
Posts: 28
Location: Texarkana, TX
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| Posted: Sat Dec 29, 2018 9:24 am Post subject: Re: Fuel gauge calibration |
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I am wondering now if my problem is the design of the JBugs sending unit. The rheostat on the short arm seems to be accurate throughout its range. However, I put the sender in a tub of water to see how the 2 float arms interact. In this test, to my eye, as it comes "out of the box without custom bending",the longer arm seems to have very little interaction with the short "active" arm. If this is so, then the gauge would drop precipitously from full to 8 gallons. And this is what is happening to me.
Of course the odd shape of the tank makes this whole idea hard to prove. |
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Blue69Baja
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Joined: September 04, 2008
Posts: 1065
Location: Fair Oaks
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| Posted: Sat Dec 29, 2018 9:12 pm Post subject: Re: Fuel gauge calibration |
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Dermodad, If you have a good DVM with ohms reading you should be able to identify what is going on with your sending unit while in the tank.
You should disconnect the output wire of the sending unit when you check the ohms. You can leave the ground lug connected.
Here is a chart for resistance for a type 2.. Resistances are close to or the same for type 1... 10 to 72ohms for ours.
I too Have a 72 Super I had to replace my OEM sending unit this year. with the double floats. 59,000 miles and 46 years finally took it out.
I replaced the sending unit, got it from Jbugs, and about 3 mos later the OEM vibrator stuck, took out my OEM fuel gauge... I was so pissed...
So here I am in the process of making the fuel gauge system work properly with parts that we get from various places... Zener regulator and after market gauges.
My car is pristine and all original stuff except the Fuel Gauge system.. Pisses me off that the parts we get do NOT WORK together properly....
I am close to start testing in car with modified Zener regulators and Non OEM Gauges...
I have two gauges working very similar and 2 very different regulators from different vendors working properly to make the gauges move full scale and quite accurately.
I do not have a sending unit I can use on the bench. I am using a variable resistor /pot.
When I installed the sending unit I verified the operation.... Empty to full.... But I did not check the angles for full 1/2 empty etc... I hope I do not get into the same issue you and some others are having...
Pic credit to SGkent, I think.
_________________
69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original..
Last edited by Blue69Baja on Sat Dec 29, 2018 9:47 pm; edited 1 time in total |
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Blue69Baja
Samba Member
Joined: September 04, 2008
Posts: 1065
Location: Fair Oaks
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| Posted: Sat Dec 29, 2018 9:19 pm Post subject: Re: Fuel gauge calibration |
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If you can pull the sending unit out that would really help in measuring the angle and resistance.
My car is all original with AC. To get the sending unit out you have to remove the tank or remove all the duct work. OMG!
Keeping everything original, hoses etc was an absolute bear...
I will check my OEM sending unit for what you are taking about with the angles of the two arms. I can not imagine the factory bending the arms to work.
Measuring OHMS is very easy with a bit of tutoring.. Youtube it or ask for help.
Jim
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69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original.. |
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72VWSB
Samba Member
Joined: August 06, 2018
Posts: 707
Location: New Mexico
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| Posted: Sun Dec 30, 2018 10:42 am Post subject: Re: Fuel gauge calibration |
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| How does one know if the fuel gauge is fried? Is there a way you can test the wires that go to the fuel sender? |
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glutamodo
The Android
Joined: July 13, 2004
Posts: 26320
Location: Douglas, WY
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| Posted: Sun Dec 30, 2018 10:52 am Post subject: Re: Fuel gauge calibration |
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Well, if you ground the wire going to the tank unit, the gauge should go to full.
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