1967 fuel gauge error and speedo error

[Donald O.]

Fuel gauge error
I have installed a new fuel gauge and a new sending unit. Before installation I verified that the resistance was 0-90 ohms through the sending unit. The issue is that when the tank is empty, verified by visually checking, the gauge reads empty, but when I added 5 gallons of fuel the needle on the gauge barely went above full. It also when filling the tank the needle does not display full, maybe just over 3/4 full. How do I calibrate the gauge to the sending unit? Bend the arm? Remove the gauge and then remove the needle to display the more correct fuel level?



Speedo error
327/350hp, M20 WR 4 speed, 3.36:1 posi, new blue gear at end of speedo cable (replacing the worn original), 205-75/R15 tires on original ralley wheels.
Tach is correct throughout its operating range verified by an electronic tach held in the cockpit.
My information says to me that at 2000 rpm in 4th gear my speed should be an indicated 46mph....BUT

I have a GPS AP on my phone and I checked its accuracy against my Buick and it was dead on (+/- 1mph). So when I checked in the Vette, at 2000 rpms the GPS was reading 53 mph.

How do I correct or calibrate the speedo? Just send it to Joe Ray and let him work his voodoo magic?

Snow season is approaching and Ill have several months disassembly-repair-reinstallation to get this corrected.


Don

[Dick W.]

Re: 1967 fuel gauge error and speedo error

NoSpaceO Joe Ray is your man on the speedo. I suspect you will have to play with your sending unit to get the gas guage correct. Just make sure your guage is reading correctly by ground it, it should read full when grounded

[Donald O.]

Re: 1967 fuel gauge error and speedo error

An the sending unit,

0 ohms = empty
90 ohms = full

Correct?

[Donald O.]

Re: 1967 fuel gauge error and speedo error

NoSpaceO Joe Ray is your man on the speedo. I suspect you will have to play with your sending unit to get the gas guage correct. Just make sure your guage is reading correctly by ground it, it should read full when grounded

Thanks Papa Smurf

[Edward J.]

Re: 1967 fuel gauge error and speedo error

Don, if you take a coat hanger and make a small hook you can open the tank and pull up on the arm it should read full, just remember bending the arm may effect the empty reading, the sender has a stop at the full and empty points.I really think the tanks are not really accurate to the gallon. generally I see a couple of gallons in tank when the gauge reads empty.

[Jeff B.]

Re: 1967 fuel gauge error and speedo error

<<Speedo error>>
<<327/350hp, M20 WR 4 speed, 3.36:1 posi, new blue gear at end of speedo cable (replacing the worn original), 205-75/R15 tires on original
<<ralley wheels.
<<Tach is correct throughout its operating range verified by an electronic tach held in the cockpit.
<<My information says to me that at 2000 rpm in 4th gear my speed should be an indicated 46mph....BUT

<<I have a GPS AP on my phone and I checked its accuracy against my Buick and it was dead on (+/- 1mph). So when I checked in the Vette,
<<at 2000 rpms the GPS was reading 53 mph.

Donald
You are correct in that if you do indeed have a 3.36 rear end ratio, at a true 2000rpm, the speedo should show about 46mph. What mph does your speedometer actually indicate when running 2000rpm? If your true speed at 2000rpm is actually 53mph, you might really have a 3.08. At 60mph, a 3.36 rear should tach about 2600, and a 3.08 should tach about 2300. Sounds like your driven gear (blue) is incorrect.

[Donald O.]

Re: 1967 fuel gauge error and speedo error

Don, if you take a coat hanger and make a small hook you can open the tank and pull up on the arm it should read full, just remember bending the arm may effect the empty reading, the sender has a stop at the full and empty points.I really think the tanks are not really accurate to the gallon. generally I see a couple of gallons in tank when the gauge reads empty.

Ed, I have done the coat hanger lift up test and only get just over 3/4 tank level displayed, plus when I added 5 gallons to an empty tank it only displayed just over empty. I don'y need it accurate to the gallon, but 5 gallons should indicate 1/4 tank and 10 gal should indicate 1/2 tank.

[Dick W.]

Re: 1967 fuel gauge error and speedo error

Ed, I have done the coat hanger lift up test and only get just over 3/4 tank level displayed, plus when I added 5 gallons to an empty tank it only displayed just over empty. I don'y need it accurate to the gallon, but 5 gallons should indicate 1/4 tank and 10 gal should indicate 1/2 tank.

You can add a resistor to correct the error. It is trial and error. It also works when you have a tanker with a bad sending unit and you need to have a PV, just saying Of course I know nothing.

[Donald O.]

Re: 1967 fuel gauge error and speedo error

So now I believe I need Joe Ray's phone number and his email addy and of course his ship to addy

Joe, if you see this thread, email or me.

DonO

[Dick W.]

Re: 1967 fuel gauge error and speedo error

Joe Ray <vettenut0071946@att.net>

[Joe R.]

Re: 1967 fuel gauge error and speedo error

Don,

e-mail vettenut0071946@att.net

cell 1 501 680-4740

Address:

Joe Ray Parts Co.
2025 Cedar Creek Road
N. Little Rock, AR. 72116

Thanks,

Joe

[Duke W.]

Re: 1967 fuel gauge error and speedo error

<<Speedo error>>
<<327/350hp, M20 WR 4 speed, 3.36:1 posi, new blue gear at end of speedo cable (replacing the worn original), 205-75/R15 tires on original
<<ralley wheels.
<<Tach is correct throughout its operating range verified by an electronic tach held in the cockpit.
<<My information says to me that at 2000 rpm in 4th gear my speed should be an indicated 46mph....BUT

<<I have a GPS AP on my phone and I checked its accuracy against my Buick and it was dead on (+/- 1mph). So when I checked in the Vette,
<<at 2000 rpms the GPS was reading 53 mph.

Donald
You are correct in that if you do indeed have a 3.36 rear end ratio, at a true 2000rpm, the speedo should show about 46mph. What mph does your speedometer actually indicate when running 2000rpm? If your true speed at 2000rpm is actually 53mph, you might really have a 3.08. At 60mph, a 3.36 rear should tach about 2600, and a 3.08 should tach about 2300. Sounds like your driven gear (blue) is incorrect.

To the OP: You should take speedo/GPS readings at several speeds from about 15-25 MPH to, say, 80 MPH in 5 to 10 MPH increments. Then compute the percent speedo error. If it is constant you have what's called a "gain error", which can usually be eliminated by a different speedo driven gear, which is easy to change. If the error is a constant speed then you have offset error that can be corrected by reclocking the needle on the pin.

You could also have a combination of both gain and offset error, but one needs an accurate test data set as described above to analyze the problem and determine a course of corrective action.

Duke

[David H.]

Re: 1967 fuel gauge error and speedo error

Don,

Link below may have some useful information, esp 66-67 gauge testing.

http://repairs.willcoxcorvette.com/category/fuel-gauge-info/

Dave

[Tim G.]

Re: 1967 fuel gauge error and speedo error

Sales brochures for Corvettes have the speed at RPM for each ratio. That helped folks order the ratio they wanted.

[Frank D.]

Re: 1967 fuel gauge error and speedo error

I had to move the face and needle of my 63 fuel gauge onto a 64 NOS movement and the repro tank sending unit was a bit off but not much. Someday I'll take the filler neck off and see if I can reach down into the tank to adjust the float for a perfect (or close) reading. Until then I'll just use some Kentucky windage to assess fuel level.... C2s are unique in using a 'powered' sending unit with a voltage divider circuit to pick off a voltage from the sending unit 'slider' to determine fuel level.....why the extra complication ? I've never heard an explanation.

C1s and C3s are simple voltage readings...