73-87 Chevy _ GMC Trucks > Instrumentation
Another gas gauge/ speedo question.
Jimartina:
1977 c10 Scottsdale 350, 4brl, th350 automatic.
Gauge pegs at over full
Ok with that said. I have replaced the sending unit. Tested the gauge and the wiring. Everything seems ok. I get 12.7 volts on the left side connector behind the fuel gauge. Like 6is volts on the right side connector and 0 volts on the bottom. From my research it seems that the sending unit is giving me reading but the gauge pegs over full every time I turn the key on. I've tested the fuse link on the back of the fauge and it tested good.
Most of my other gauges work, dash lights and all signals work, as well as dimmer switch.
Speedo was working at highway speed and suddenly stopped. Used drill to turn speedo and it moves like it should. Bullet and gear appear to be ok. I can see the gear inside the output tail on trans and it appears ok, (can't really tell for sure) before I take the tail piece and drive shafts off do I need to do something else?
Thanks in advance everyone.
Big Dee:
:)
Is the gas tank full ? that would make the gauge read full.
Have you serviced the cable. a drop of oil can cure a gallon of problems.
:D
bd:
The fuel gauge probably has an open somewhere in the sender circuit. With the ignition switched on, jump the fuel gauge sender pin directly to ground. The gauge should rapidly drop to Empty. Check the PCB-to-gauge connections and the I/P cluster harness-to-PCB connections. Burnish the copper foil and terminals at the points of electrical contact using a soft rubber eraser, if necessary. But be careful not to peel the foil away from the plastic substrate; it's an easy mistake to make.
Now is a great time to lube the speedometer cable! Make sure the cable is fully seated onto the back of the speedometer head. When you stated that you "used a drill to turn the speedo and it moves like it should," was that with the drill motor attached at the transmission end of the cable? It is very rare for the speedometer drive gear to fail without causing visible wear of the driven gear. However, the drive gear may have shifted axially on the output shaft of the transmission if its retaining clip failed or was not properly installed during prior assembly. Peruse the article, "Common causes of 'bouncy' speedometer needles" for additional insight.
Jimartina:
--- Quote from: Big Dee on April 15, 2022, 10:56:38 AM --- :)
Is the gas tank full ? that would make the gauge read full.
Have you serviced the cable. a drop of oil can cure a gallon of problems.
:D
--- End quote ---
3/4 full, but good question. Cable seems to move freely.
Jimartina:
--- Quote from: bd on April 15, 2022, 11:16:06 AM ---The fuel gauge probably has an open somewhere in the sender circuit. With the ignition switched on, jump the fuel gauge sender pin directly to ground. The gauge should rapidly drop to Empty. Check the PCB-to-gauge connections and the I/P cluster harness-to-PCB connections. Burnish the copper foil and terminals at the points of electrical contact using a soft rubber eraser, if necessary. But be careful not to peel the foil away from the plastic substrate; it's an easy mistake to make.
Now is a great time to lube the speedometer cable! Make sure the cable is fully seated onto the back of the speedometer head. When you stated that you "used a drill to turn the speedo and it moves like it should," was that with the drill motor attached at the transmission end of the cable? It is very rare for the speedometer drive gear to fail without causing visible wear of the driven gear. However, the drive gear may have shifted axially on the output shaft of the transmission if its retaining clip failed or was not properly installed during prior assembly. Peruse the article, "Common causes of 'bouncy' speedometer needles" for additional insight.
--- End quote ---
Great thx. I'll try that and see what happens.
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