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Stock speedo twitching

So apparently something is going bad in the car and I assume it's ground related. How exactly does the speedometer/cluster move? Apparently if I'm on a long drive (traffic), when stopped, the speedometer twitches a little. If I have my marker lights on, it twitches up to 10mph once every second or two. If I have the headlights on also, the speedo rests at about 10mph and twitches up to 20mph, while stopped. This does not happen all the time but it appears to be fairly consistent if I am sitting still for long periods of time. Once I start moving, the speedo behaves normally. Turning the lights off makes it drop back down. Alternator normally puts out 14.5v at idle but drops to 14v at this time of stop and go driving, with the lights off, and 13.7v with them on.

Where would I start to troubleshoot this behavior?
1988 Thunderbird Sport

Stock speedo twitching

Reply #1 –
Up ^
1988 Thunderbird Sport

Stock speedo twitching

Reply #2 –
good question.. the needle in the vert speedo does the same thing but not as severe.
Is yours a digi speedo?
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***** Project "EVOLUTION" 1987 Cougar LS  & 1985 Cougar Convertible *****
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5.0 HO 306 roller block, machined GT-40P heads, Wiseco dished forged pistons, Eagle forged floating I-beam connecting rods, Lunati pushrods, ARP bolts, Scorpion aluminum 1.6 rockers, Comp Cams Magnum 266HR, Explorer intake, 65mm TB, MAF Conversion, 19# injectors, Ford Racing stainless P-headers, 2-1/2" cat-less exhaust w/ Flowtech Afterburner lers , SC AOD with 2800 BDR torque converter, 3.73 T-Lok rear, CHE rear control arms, full 2-1/2" frame w/1" jacking rails & seat supports, Rear disk brakes, Turbine wheels, All original interior w/ floor shift upgrade .......
Pretty much every panel on my 87 is new, rebuilt, or re constructed. :D
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Stock speedo twitching

Reply #3 –
Stock buttstuffog from the 88 Sport. Most of the time it sits at 0mph and twitches a little - I've seen that more lately than the more severe issue. I don't drive the car often, especially at night, so I don't have any further information.
1988 Thunderbird Sport

Stock speedo twitching

Reply #4 –
Then it's the same thing. mine will also get to 5mph idling in park. the vert had a swap from digi cluster to buttstuffog. I figured maybe something was not connected good somewhere. I plan on ripping through that car after my 87, so I wasn't that concerned right now. But I would like to find out why. maybe the tension on the needle is weak and vibrates randomly. That was my original thought when I saw it happen.
[SIGPIC][/SIGPIC]
***** Project "EVOLUTION" 1987 Cougar LS  & 1985 Cougar Convertible *****
[/COLOR]
5.0 HO 306 roller block, machined GT-40P heads, Wiseco dished forged pistons, Eagle forged floating I-beam connecting rods, Lunati pushrods, ARP bolts, Scorpion aluminum 1.6 rockers, Comp Cams Magnum 266HR, Explorer intake, 65mm TB, MAF Conversion, 19# injectors, Ford Racing stainless P-headers, 2-1/2" cat-less exhaust w/ Flowtech Afterburner lers , SC AOD with 2800 BDR torque converter, 3.73 T-Lok rear, CHE rear control arms, full 2-1/2" frame w/1" jacking rails & seat supports, Rear disk brakes, Turbine wheels, All original interior w/ floor shift upgrade .......
Pretty much every panel on my 87 is new, rebuilt, or re constructed. :D
Join us on Facebook
http://www.facebook.com/home.php?sk=group_137541156293768&ap=1

Stock speedo twitching

Reply #5 –
After the dash swap in the Sport, mine did this as well.

Turned out to be a ground on the lower right of the center stack that wasn't cleaned/connected securely.
The sheet metal on the dash itself had some surface rust...a quick rip with a piece of sandpaper and put some tight on the screw and all was/is well again.

Hopefully this is what ails you'ns.
'98 Explorer 5.0
'20 Malibu (I know, Chevy, but, 35MPG. Let's go brandon, eh)

Stock speedo twitching

Reply #6 –
I'll look into that on mine
[SIGPIC][/SIGPIC]
***** Project "EVOLUTION" 1987 Cougar LS  & 1985 Cougar Convertible *****
[/COLOR]
5.0 HO 306 roller block, machined GT-40P heads, Wiseco dished forged pistons, Eagle forged floating I-beam connecting rods, Lunati pushrods, ARP bolts, Scorpion aluminum 1.6 rockers, Comp Cams Magnum 266HR, Explorer intake, 65mm TB, MAF Conversion, 19# injectors, Ford Racing stainless P-headers, 2-1/2" cat-less exhaust w/ Flowtech Afterburner lers , SC AOD with 2800 BDR torque converter, 3.73 T-Lok rear, CHE rear control arms, full 2-1/2" frame w/1" jacking rails & seat supports, Rear disk brakes, Turbine wheels, All original interior w/ floor shift upgrade .......
Pretty much every panel on my 87 is new, rebuilt, or re constructed. :D
Join us on Facebook
http://www.facebook.com/home.php?sk=group_137541156293768&ap=1

Stock speedo twitching

Reply #7 –
I would second the ground as a good starting point.

On a stock digital speedo, the unit updates 6 times a second. Obviously the buttstuffog is a little different than that. But both get their direct input from the VSS in the transmission housing. Sometimes the VSS starts to go bad and will feed the speedo input at idle (zero), or the speedo driven gear on the end of the VSS can lose teeth and do the same. I've seen both happen, and on the digital speedo the numbers flicker at zero speed (and likewise, the needle can bounce on an buttstuffog speedo).

Also, you cannot discount the IVR behind the cluster, nor can you discount the ignition switch or the voltage regulator (alternator).

Any of these can cause the problem, but your fix is likely somewhere in there, since you've already determined that your alternator and charging system are working properly.

However...gut feeling says that if you notice the problem with the headlights on, but it goes away with the headlights off, chances are it's the IVR. It's pretty sensitive to minute fluctuations in voltage sometimes.

Stock speedo twitching

Reply #8 –
I'll check mine with the lights on... I haven't had to turn them on yet.
[SIGPIC][/SIGPIC]
***** Project "EVOLUTION" 1987 Cougar LS  & 1985 Cougar Convertible *****
[/COLOR]
5.0 HO 306 roller block, machined GT-40P heads, Wiseco dished forged pistons, Eagle forged floating I-beam connecting rods, Lunati pushrods, ARP bolts, Scorpion aluminum 1.6 rockers, Comp Cams Magnum 266HR, Explorer intake, 65mm TB, MAF Conversion, 19# injectors, Ford Racing stainless P-headers, 2-1/2" cat-less exhaust w/ Flowtech Afterburner lers , SC AOD with 2800 BDR torque converter, 3.73 T-Lok rear, CHE rear control arms, full 2-1/2" frame w/1" jacking rails & seat supports, Rear disk brakes, Turbine wheels, All original interior w/ floor shift upgrade .......
Pretty much every panel on my 87 is new, rebuilt, or re constructed. :D
Join us on Facebook
http://www.facebook.com/home.php?sk=group_137541156293768&ap=1

Stock speedo twitching

Reply #9 –
Quote from: EricCoolCats;328471

However...gut feeling says that if you notice the problem with the headlights on, but it goes away with the headlights off, chances are it's the IVR. It's pretty sensitive to minute fluctuations in voltage sometimes.


This is what causes the three gauges to shoot up also, right? I guess it's about time I fix that thing then as that's also a slight annoyance.
1988 Thunderbird Sport

Stock speedo twitching

Reply #10 –
I  haven't touched this yet but figured I'd upload a video of the behavior. CLICK HERE to see what happens in a warm day with A/C on, blower on high, at idle, headlights and everything off. It can get quite bad and is apparently getting worse. I'm not worried as much as the sing noises I've got coming from the front drivers side - hopefully I can get the source pinpointed in the next few days.

Also like my useless oil pressure gauge? It did this with the stock motor too. Mechanical gauge shows no problem.
1988 Thunderbird Sport
 

Stock speedo twitching

Reply #11 –
ill be watching the results on this one.

my 90 bronco use to have an E40D but now has a 5 speed from a 92 f150. 

the speedo gear or something makes the needle twitch and bounce.  eventually the gear is worn out.