fuel gauge dampening

[61bugsey]

The fuel gauge on my '61 Bugeye is very erratic. New sending unit, new gauge, new wiring, and good ground. On level ground it is accurate and stable but when in motion the needle is all over the place. Anyone know how to dampen the fluctuations in the needle?

Thanks,

Dave

 

[dklawson]

I don't know if it is possible. The later gauges are inherently slow and dampened because they work by resistance heating of internal bits. The early gauges basically work using electromagnets to pull the needle around.

You could try installing various sizes of electrolytic capacitors between the "T" terminal on the fuel gauge to chassis ground (pay attention to the capacitor's polarity). That may slow the response time of the gauge due to rapid movements of the float. Maybe. However, the needle itself is still positioned by weak electromagnetic forces so bumps may still cause the needle to bounce just because of its own mass.

If he doesn't post to this thread, send a message to Steve Maas (Sarastro) as he might have some ideas on how else you might electronically dampen the needle.

 

[Jim_Gruber]

Kim from SC who goes by regularman is the Spridget semi expert on fuel gauges. Let's see if he can chime in. I'd consider finding an old gauge to stick in there. I replaced my sender with one of the new plastic MOSS Units. It works fine with the old gauge. There are different gauges and senders and they need to be a matched pair to work properly. Different senders put out dramatically different +/- ohms readings when full or empty and if not matched they just won't work correctly.

 

[smaceng]

Just remember one can not use an old gauge (i.e. Bugeye and a little later) with the newer sending unit or a newer gauge and an older sending unit. They will read backwards....reads full when empty and visa versa. I bought one of the sending units recently manufactured and sold by the big two, and it lasted a couple of years. I'm going to have an original Smith unit rebuilt when I get the courage and strength to remove the tank again.
Scott in CA

 

[61bugsey]

OK thanks.
I'll dig around in my old ham radio junk boxes and pull out a few electrolytic caps and play around.

Dave

 

[61bugsey]

After I try the caps, I'll see if I can scrounge an older gauge from a buddy and give that a try.

Thanks for the info!

Dave

 

[dklawson]

Kim from SC who goes by regularman is the Spridget semi expert on fuel gauges.

I haven't seen Kim post in a while. Of course, you can always send him a PM so he will see the message in his inbox when he does check in on the board.

Oh... he's from NC, not SC.

If Kim doesn't check in for a while, Google for "MGA Guru" and visit Barney Gaylord's web site. His web site has quite a lengthy explanation of the early fuel gauge and how to repair and calibrate it.

 

[Billm]

Dave
Since you were talking about it I decided to notice mine-
I have a '65 Midget which probably has the same gauge that you have.
I noticed that mine waves all over the place (about 1/2 tank now) but I have also noticed that it doesn't wave much at "empty" which is all that I care about.
BillM

 

[regularman]

One reason it jumps around is not the float moving but the fluxuation in voltage. Its why they went to the 10v gauge and the voltage stabilizer in the later models. When you say everything is new. Is the sending unit an aftermarket one or the original one. Sadly, new is not necessarily better. I cannot say for all aftermarket ones but I have seen some of poor quality. Both old an new have a wiper that moves along a wire wound resistor. The old ones had a wiper with two contact points, one on each side. The newer one had only one wiper touching on one side of the resistor and if there is any lateral movement in the mechanical part of the wiper, it loses contact and makes the needle jump around during car movement.

 

[61bugsey]

Kim,
The new one I put in, along with the new fuel tank, was indeed aftermarket. And, it does have the wire wound resistor. It has fluctuated erratically from day 1 ( which was about 2 years ago). That could very well be the problem if the contact is "making and breaking" along the resistor. Next time I am bored and feel like dropping the tank, I'll look at that. Odd thing is, I've been retired for 5 years and haven't been bored yet. Sounds like a good winter day project.

Thanks for you help!

Dave

 

[Sarastro]

I don't know if it is possible. The later gauges are inherently slow and dampened because they work by resistance heating of internal bits. The early gauges basically work using electromagnets to pull the needle around.

You could try installing various sizes of electrolytic capacitors between the "T" terminal on the fuel gauge to chassis ground (pay attention to the capacitor's polarity). That may slow the response time of the gauge due to rapid movements of the float. Maybe. However, the needle itself is still positioned by weak electromagnetic forces so bumps may still cause the needle to bounce just because of its own mass.

If he doesn't post to this thread, send a message to Steve Maas (Sarastro) as he might have some ideas on how else you might electronically dampen the needle.

I think Doug has given precisely the answer I would have given. I'd find a 10,000 microfarad capacitor (the value is not critical; anything close to this is OK) with at least 15V breakdown, and connect it between the terminals of the meter. Be sure to observe polarity. Won't cost much and it's worth a try.

The indicator needle of the fuel gauge on my bugeye bounced around quite a bit, too, but the fluctuations weren't unreasonable. Maybe plus or minus a quarter tank, and when the car stopped it quickly got steady. And, of course, it wasn't very accurate to begin with. To some degree, this is just the nature of the beast--these cars are imperfect in a lot of ways, and this is just one.

 

[61frogeye]

My BE, with original sender and gauge,bounces a bit, but not too bad. It bounces more erratically in the last 1/4 of the tank. The nice thing is I can run it all the way to an indicated "empty" and I still have a little less than a gallon still left in the tank.

 

[regularman]

Kim,
The new one I put in, along with the new fuel tank, was indeed aftermarket. And, it does have the wire wound resistor. It has fluctuated erratically from day 1 ( which was about 2 years ago). That could very well be the problem if the contact is "making and breaking" along the resistor. Next time I am bored and feel like dropping the tank, I'll look at that. Odd thing is, I've been retired for 5 years and haven't been bored yet. Sounds like a good winter day project.

Thanks for you help!

Dave

Then it will be too cold to do it. I thought of cutting out a square hole in the trunk just to get to the sender and make a gasketed patch plate to go over it. That way you don't have to pull the tank. That would be a good thing to throw in when doing a resto when you got all that off already.

 

[61bugsey]

Hey, that's a good idea. Although I spent 3 years on a total restoration of mine, that certainly would have been a good time to do that. Heck, I had so many holes in the boot I wouldn't have had to cut another hole. I just would have had less to weld back in.

 

[nomad]

Dave
Since you were talking about it I decided to notice mine-
I have a '65 Midget which probably has the same gauge that you have.
I noticed that mine waves all over the place (about 1/2 tank now) but I have also noticed that it doesn't wave much at "empty" which is all that I care about.
BillM

Agree with you, Bill. My first Brit car was a MG TC and the fuel guage consisted of a light that came on when you had about 50 miles worth of gas left. Worked great and I never ran out of gas.
Its only the last bit that counts!

Kurt.