Gas gauge bouncing

[beetle1960]

I appologize if this has been discussed here before, I did a search but did not get a clear answer.

My fuel gauge on my 70 c10 bounces like crazy when moving, like half the gauge swing crazy, thought it was ground issue so I ran a ground wire from sending unit to the body, no change. I then purchased a new sending unit from LMC, no change. I have had many older vehicles (got my license in 1976) and I don't ever remember this being "just the way it is" with older vehicles. thoughts?

[tommys72]

Thats how mine does too....I chalked it up to old technology and sloshing fuel
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[68gmsee]

One question, does it only bounce when driving around and remains steady when parked?

Neither one of my trucks had/have a bouncing fuel gauge and I drive through quite a few dirt/gravel roads. The first thing I'd do is make sure there's a good ground from the cab to the engine back to the negative battery. Also, on the back of the gauge cluster there should be a ground wire going to the cab. After that, look for loose connections behind the cluster.

[wesmigletz]

I was having problems with my gas gauge. The connector that plugs into the fuse box was bad/loose. I put a new female spade connector on and it fixed my intermittent gauge issue.

[beetle1960]

steady when still..only bounces while driving. New ground straps from block to cab and to frame. I did put a ground wire from sending unit to cab. Didn't know about ground on cluster, I know I did not ground cluster because I put the cluster in. I will do that.

[68gmsee]

Originally Posted by beetle1960

...... Didn't know about ground on cluster, I know I did not ground cluster because I put the cluster in. I will do that.

Not all trucks have them. My 69 did but my 68 didn't. I guess it's a "just in case" type thing.

One other possibility, if you don't find any loose wires or connections, may be a problem with the fuel gauge itself, gauge printed board or wiring behind it.

[wgr2112]

On the back of the cluster, there should be a resistor between the 2 connectors on the back of the gauge. This is designed to even out the current sent from the sending unit.

If your new cluster doesn't have this, that is most likely they problem.

[68gmsee]

One more final test if all the above fail to resolve.

Remove the gauge cluster and check all the lands and connections to insure they're not broken or loose.

Remove the front cover being careful not to lose the cardboard light covers.

Check the needle on the fuel gauge. It should have a slight resistance when you try to lightly move it. Tap or shake it to see if it bounces. If it moves freely, the needle itself may be lose or the gauge asm will need to be replaced. They're about $30 at LMC not sure about other vendors.

I checked two fuel gauge ceramic resistors between the mounting posts. After I removed them one measured app 77.8 ohms the other one measured 85 ohms.

[cool68]

where do you put ground from gas tank sender to cab ?. I do not see any tabs or screws to attach wire to near sender.