Got a gremlin. Noticed that my voltmeter needle jumps a bit when the car is in motion. The faster it goes the faster the needle jumps. Does not seem to have anything to do with engine speed, just the actual driving speed. Any ideas?

 

Jenyap: MY? Description with accessories that may be in use during these swings?

I find that my voltage reading varies between 12.5 V and a little over 14V, and that is with new brushes/regulator/capacitor. The peak reading with all accessories enabled is about 13.7 V.

 

All other things equal the needle jumps slower at slower speed, faster with faster speed. Does not jump at all when the car is not in motion. BTW the car is a 86.5 auto with a delco alternator.

 

Mine does the exact same thing on a 85/ 5-speed. It shakes like it has parkinsons. Not making fun, just a good description. It always reads low even though it is charging fine. Its been this way since I owned the car, 1.5 yrs now.

 

what was the last thing that you fixed?
From your description it sounds like it may be getting a pulse from the speedo.

 

Our 86 does it, also. Figured it was either wire short in harness around engine or in pod. Interesting idea, Stan, that it could be an interference signal. My son and I changed alternators with an absolutely known good one, had the SAME issue. No Change. Its likely not your alternator.


Whoa. Wait a minute. How did you match a Delco alternator to the 5.0 liter block on and 85 or later car. We need some detailed pictures on this one. Stat.

 

Shark Attack,

Did you ever solve this problem? My 86 is the same - guage reads low and bounces.

I thought I remember a thread that said there is a spring in the guage that fails. I am looking for the thread but I can't find it. Anyone????

 

I've got the same problem, and I've noticed numerous threads on this issue. I've replaced the alt., resistor, printed circuit board, and cleaned everything . . . still the same. Next time I have the pod off, i may try the gauge!

 

Could be a bad ground(check them all per the WSM) or the power leads at the top of the CE panel or jump post are loose. Could be a loose terminal on the battery or alternator. If it still does the same after checking those items, connect a multimeter to one of the + posts on the top of the CE panel and see if it misbehaves too(really cheap meters might not show the variation). If not, the problem is between that point and the gauge. If so, the problem is one of the other things I mentioned, or maybe the voltage regulator on the alternator. Can you post a vid, even a cellphone vid, to show the gauge behavior? Descriptions are very subjective, but observing the actual behavior might help narrow it down.

 

My needle has done the same thing for a long time. I've gotten used to it - sort of a friendly little wave from the dash. And never any under/overcharging problems, so I've just ignored it, although I've followed every relevant thread wondering if someone would find a fix. Now I have! Last week I hit a large clump of ice on the road (no time to stop or room to maneuver) left of center (i.e. alternator vicinity) and now the needle is rock steady, shows charging/discharging as it should, and the alternator is still performing correctly.

OK, now it's time for theories - anyone?

 

Well, you know mine was fixed when we found the excitor wire hanging by a thread where it was soldered into the 14 pin connector.

 

Martin, did you have the belly pan on when you hit the ice?If not, maybe it torqued a wire around so it was making better contact?

The needle will normally move around some as various things switch on and off.

Chris H, it's probably not the gauge. The gauge is simply responding to the voltage that it sees.

 

I searched for info on a voltmeter spring and could not find anything. I think my memory must be wrong about a spring failure problem.

I just watched my needle careful and determined that it is effected by vehicle speed. And in fact it not merely bouncing, but it actually pulses. At ~ 10mph, it pulses ~ once per second. Therefore, it must be electrical and not due to a spring problem. Next I will remove the pod and clean connections.

 

Belly pan!? I don' need no steenkin' belly pan...

 

any updates to this thread?
I have an 85 with a bouncy alt gauge,
still charges fine, I had the alternator rebuilt as well no change all the grounds cleaned