Speedometer needle bouncing at idle?

[adamj]

Why would my speedometer needle be bouncing or even moving at all when the vehicle is stationary? The speedometer cable should not be rotating at this point, correct? Is there something else that affects the speedometer? I recently removed and installed my gauge cluster, so maybe I did something wrong. There's this connector that screws in near the speedo that has red and green wires I think.

 

[bucket]

I think your burb is magical

Honestly I have no idea, I don't see how it would be possible. The thing that screws in the back of the speedo is the VSS though. The TBI uses it and maybe the cruise too if you have it.

 

[adamj]

Ok, I will be taking cluster out and checking the connection.
For the VSS, how important is that screw? I lost the little single black screw that holds it to the cluster and used something close, but it's not perfect, I think that could be it. I don't have cruise, but does TBI use that speed input for fuel trims?

Also, is it normal for the speedometer to go "negative" when reversing?

I will be looking for a new speedo soon, I think mine is going bad - even with new cable, it is still bouncy.

 

[smoothandlow84]

Your transmission spins at idle, just not engaged. I think you have a bad speedo drive gear. Its possible that the plastic gear/cog is broken and jammed enought to engage the speedo cable enough to cause it to bounce. As far as it moving in reverse...once again take apart the mechanism that the speedo cable threads into at the transmission housing under the truck. Its easier with two people to verify that the cable, when spinning activates the speedo correctly. If the cable bounces when turned, the cable itself is binding and in need of replacement. The speedo cable housing can be saved. New cables are under $20 at the local auto parts stores. The connection at the transmission is probably the culprit to the problem at idle.

 

[Georgeb]

Your transmission spins at idle, just not engaged. I think you have a bad speedo drive gear. Its possible that the plastic gear/cog is broken and jammed enought to engage the speedo cable enough to cause it to bounce. As far as it moving in reverse...once again take apart the mechanism that the speedo cable threads into at the transmission housing under the truck. Its easier with two people to verify that the cable, when spinning activates the speedo correctly. If the cable bounces when turned, the cable itself is binding and in need of replacement. The speedo cable housing can be saved. New cables are under $20 at the local auto parts stores. The connection at the transmission is probably the culprit to the problem at idle.

Except the if your parked at idle the tailshaft of the trans isn't turning so the speedo shouldn't be moving at all.

 

[adamj]

The bouncing while parked has gone away, so has the bouncing needle at speed.
I guess it worked itself out!

 

[smoothandlow84]

Hmmm....the gremlins have left the burb

 

[bucket]

Like I said before... Magical!

 

[adamj]

When stopped, where should the needle be? At the 5mph tick? Or below that?

 

[bucket]

Can't say I've ever paid much attention to that. I want to say they've all kinda flopped to the bottom. I know they've all had their own personalities.

 

[adamj]

I know some speedo's from other vehicles have a little peg that stops the needle from going so low, do our speedos have something like this? Mine's kind of old and I can't tell if the peg just snapped off or something.

 

[bucket]

No peg.

 

[TheGolem]

I hate to hijack this thread, but does anyone else feel like their speedometer reads slow? For example; when I think Im driving the speedlimit, everyone else seems to be driving too slow. or maybe the rough ride just makes the truck feel like its moving faster? its an 87 V10

 

[GTME94]

My speedo is off. Pretty common with these old trucks with changes to tire sizes, axle ratios, etc. I used a GPS speedometer app on my phone to figure out true speed. Mine reads about 5 mph slower than actual speed at around 60-65 mph so I just drive about 5 over all the time.