I figured I would post my experience on getting my "bouncing" fuel gauge repaired, as maybe what I learned will help others.　

When I bought my 1987 Camaro five years ago, I noticed that the fuel gauge bounced around when the car moved. When the car was stationary, the gauge read accurately, but it was hard to read it when the car was moving, as the needle on the gauge was constantly moving up and down. (After a sudden stop, the needle could literally bounce back and forth from almost E to F.)　

I read a lot of thirdgen articles on bouncing fuel gauges. Usually I get a lot of good tips by reading thirdgen.org, but in this case there was a lot of confusing information (and even some wrong information). Some said that all third gen fuel gauges bounce around like that, so it should be accepted as "normal". In the 1980s, I learned to drive on my father's 1982 Berlinetta, so I knew that was not true. I do recall that the gas gauge reading would go up a bit (slowly) when the car was accelerating (or going uphill) and would go down a bit when the car was braking (or going downhill). But it was not normal for the gauge to jump up and down in an underdamped manner ("bouncing").　

Apparently a fuel gauge jumping around can be caused by multiple things (a sender in the tank going bad, wiring problems, etc.). However, if the gauge always is accurate except for tracking the sloshing of fuel in the tank, I believe the problem is lack of fuel gauge dampening. There also seems to be confusion about how the fuel gauge is dampened. Some said the sender provides dampening, while some mentioned a capacitor in the instrument panel. The correct answer for most third gens is that the fuel gauge is mechanically dampened. Almost all GM fuel gauges (from after 1965 up to at least the early 1990s) included some high viscosity silicone fluid to slow down ("dampen") the gauge movement. Over time, that fluid can disappear (perhaps due to a leak or evaporation), and then the fuel gauge movement is too fast and underdamped.　

One sure giveaway that the gauge has this problem is that the needle moves much too fast. For instance, if the needle is on E, and the tank is full, it should take at least a few seconds to rise to F when the ignition is turned on. In my case, it was very fast (probably 0.1- 0.2 seconds). The gauge has to be slowed down so that it filters out the sloshing of the fuel.　

After calling a few instrument repair places, I found that Nichols Speedometer and Instruments (Greensboro, NC) had the tool required to inject the silicone fluid back into the fuel gauge. I sent the whole instrument cluster to them to have it checked out and possibly calibrated, though they later said the only thing it needed was the silicone fluid in the fuel gauge. In any case, I reinstalled all the gauges back in the car, and sure enough, the fuel gauge no longer bounces around. It only rises and falls a bit during acceleration and braking (just as I remember our 1982 did), but the motion is pretty limited and very slow and damped.　

The C2 Corvette guys are well aware of this problem, so they talk a lot about getting the fuel gauge redampened by a professional gauge restorer. But our fuel gauges work exactly the same way, so the solution is the same.

 

Bookmarked this thread. Thanks!

 

Gee , and all this time I thought the only thing silicone was good for was pumping up girl's chests , Thank You for the tip !

 

I put an aftermarket fuel gauge from autometer in and it bounces like crazy when driving. I wonder if there is a way they could add it to a gauge or if I'm stuck with it as is. You would think aftermarket would be able to have some dampening especially for what you pay.

 

Apparently the original GM gauges were designed to hold the silicone fluid in a plastic cup. You can't see the cup without taking the gauge apart, but someone on a Corvette forum did take one apart.　
For instance, take a look at post #44 at this link:　
https://www.corvetteforum.com/forums...bounces-3.html
You can see the yellow plastic cup. 　

One possible issue with an aftermarket gauge is that it may not have a cavity to hold the fluid in place.　
Do you know if your aftermarket gauge has any fluid?

 

I have a new cluster in my car with speedhut gauges and the fuel needle moves all over the place.

 

It looks like the mystery might finally be solved. Thanks.

 

Interesting. My fuel gauge has the opposite problem: Takes 15 minutes to reach "F" when I fill the tank (before and after new sending unit installed). Perhaps the silicone fluid in my gauge is too thick?

 

If I were you, I would do the following test. After the needle finally reaches "F", I would shut the car off and gently push the needle (I used a Q-tip) down to E.
(Of course, you have to take off the clear plastic cover to reach the needle.)
Then I would turn the ignition on and see how fast the needle returns to F. If it again takes more than a minute, your problem is indeed probably in the gauge.
If it rises to F in less than 10 seconds, the gauge is probably okay, and your problem lies elsewhere.

If the gauge really is that slow, I suppose overly thick silicone could do that, though I don't know if that typically happens to silicone. (Apparently my problem is much more common.) But I suppose dirt or corrosion might hinder the gauge's movement as well.

 

I tested the original gauge as well as one I bought off EBay and they both took forever to do a full sweep. Just used a 12v battery and some fixed resistors. I may take the extra gauge apart to see if there is anything there to address. The gauge also only goes to 3/4 on a full tank. I finally gave up and added a 6 ohm resistor in line with the sender wire. The gauge is now accurate, but still painfully slow.

 

Well, it sounds like you did isolate the problem being in the gauge since you directly connected it to a 12V source and some resistors. It seems
unusual (very bad luck!) that even the second gauge is so slow, as it seems that loss of dampening (my problem) is much more common, based on reading many online threads and talking to instrument repair places. I guess you may need to take apart the extra gauge. (Either that, or try buying another one -- someone on thirdgen.org is selling gauges under the classifieds.)

 

You can send the gauge to speedhut and they will add a resistor to lessen the movement. They did this for mine and all it cost me was shipping.