my gas guage in my 72 442 is constantly moving while i am driving making it hard to tell how much gas is left. this is a rally pac i dont know if this means anything any help would be great thanks

 

Welcome!

Do any of your other gauges do this? Do they work right?
If they are okay, then check the ground connection to the tank sender. Remove clean and reinstall. Check wiring at the back of the gauge cluster - remove the big plug. Sometimes pins can loosen.
If all is okay and problem persists, then the tank sender may be bad.

 

My gauge does the same thing. The owner before me put a new fuel tank in the car, I'm assuming a new sender and so forth, I think the aftermarket tanks and the aftermarket senders are prone to do this, especially when below 1/2 tank. Just my .02 cents.

 

Could be caused by sloshing of the fuel in the tank. Were the factory tanks baffeled?

 

Factory tanks I think were baffled. I never had any bouncing of my gauges, whether rally pac or granny pac...

 

I have a similar issue with my Camaro. The tank is original but I replaced the sender. Once the needle moves away from Full, it bounces. I don't think it is ground with my issue, and I suspect a faulty sender. I am kind of stuck since I can't return it, and my old one, the steel line was rotted.

I would suggest checking the ground, and maybe testing with another working sending unit.

 

One other possible issue - there is a mechanical voltage regulator on the back of a factory rally pac to help steady the needles. This may have gone bad...

 

I think this is the reason. Gas tanks have baffles in them to minimize the sloshing of fuel to keep the gauge from doing just this. It's possible one (or more - I don't know how many there are) baffles in your tank has come loose. A new sending unit can also do this as replacement models I've seen aren't dampened as well as original units were, so as you go around corners, up and down hills, and accelerate and decelerate, the fuel sloshes and the float goes up and down.

 

The CSM shows a typical tank and there's a slosh baffle across the middle.

They've always done that moving around thing a little, it should read okay when you're stopped or driving on a smooth straight road ?
What's the problem?

 

I have the same problem with my 69 ninety eight after around half a tank. Would I be looking at the same things to fix this problem? Only my gas gauge does this, all others seem to be working fine.

 

My 71 does the same thing. I had a leak so I dropped the tank. (Old fuel lines were the problem.) I wanted to check the tank out anyway. Pulled the sender it was fine and looked in the tank to see if any problems or loose baffles that would cause the needle to jump. No problems with the tank. I think it is the design and tech. of the day. I just live with it.

Larry

 

My 1970 is also the same way, sometime jumping by 1/4 tank. I have cleaned and flushed the tank and replaced the sending unit with no change.

 

I've read in one of the owner's manuals that some swinging is normal. However, my understanding is that the issue is in the gauge itself, not the sender. Whatever dampens the needle wears out over time. There are services that can rebuild/repair gauges, if you are up to yanking out the dash.