Speedometer spiking while driving

[josh817]

Before we go any further, yes my speedometer is off because the tire selection I made. It's 10MPH fast so 30MPH in real life reads 40 on the gauge. I don't really care about that.

Now it's starting to jump. I don't mean bouncing needle syndrome. I will be cruising at 40MPH on the gauge, hit a bump, take a turn, sometimes don't do anything at all, and it spikes to 50MPH or 60MPH, no speed change, no RPM change, just cruising...

It won't return until I come to a complete stop. When I get moving again it will be fine until right around 40MPH and then spike again. It isn't predictable, sometimes I can drive without it happening, sometimes it happens at 40MPH on the gauge, sometimes at 50MPH, I haven't seen it happen before 40MPH on the gauge though.

Yesterday I took the cable out of the sheath, inspected it, cleaned and greased it and installed. Checked to make sure there weren't any sharp angles, but it happened again today. I will post a quick video of it when I get home in a few hours.


Ideas?

[datzenmike]

It stays at 50 and doesn't come down until you stop? Can you go above 50?

 

Needle is sticking I would think. Not the cable or drive.

[josh817]

No the needle will increase, it just creates a new offset.

So if my standard is 30MPH real life, reading 40MPH on the gauge, and then it spikes to 50MPH. If I don't stop, and I speed up to 60MPH real life, the gauge will now read 80, rather than 70. Until I come to a complete stop.

 

I thought make the cable was sticking and getting wound up and unwinding itself but I figured that would be a temporary unwinding where it reads fast until its back to normal or gets binded again (from a bump or a turn). But it will stay reading extremely fast for an hour of highway driving showing no signs of returning to normal until I come to a complete stop. And you can see when you get into the 40MPH range on the gauge, it starts getting twitchy like it wants to spike but its waiting for the right jossle...

Are there any other springs/coils/something that could be getting wound up? I figured it was a cable with gears on both ends so the only room to have this behavoir is in the cable since with gears, if they're stripped, won't read at all or intermittently.

[MikeRL411]

Many years ago I had a similar symptom. In my case I took it to a speedometer repair shop. It turned out that the braze or solder connection [don't remeber which type of connection] between the input shaft and the copper drag cup of the speedometer unit had developed a crack and the cup would wobble at certain speeds thus messing up the eddy current and causing the fluctuation needle. At rest, the cup went back to its normal position and all was well until the uneven stresses on the shaft joint started wobbling again. The fix was a simple silver solder repair to the cup to shaft junction. Hope your problem is as simple to fix.

[josh817]

[mrbigtanker]

Did you take the speedo apart.is it binding,take the cable apart and spin it freely also spray lube down the cable,last resort would be the cluster.

[josh817]

Yep I removed the cable. took it out of the sheath thing. No damage to the cable, cleaned it, greased it, reinstalled. Zip tied it in place so it can't bounce and create temporary sharp angles.

Looks like I may be taking about a speedo. Read fine on the way home last night. Will see this weekend when I have to drive an hour. Very sporadic occurrence but the days it feels like acting up you can be assured it will do it the entire trip.

[wayno]

Have you had the instrument cluster apart, were you drilling near it, you see it has a magnet that will attract metal dust/shavings, once that gets on the magnet/magnets, it don't work right no more. 

[josh817]

Nope I haven't had it apart or drilled near it since like... 3 years ago when I was putting the dash together. If it's something I can take apart and get back together after cleaning, then maybe I try that.

 

Stupid question, what are the magnets for? Is it electronic inside?

[wayno]

Nope I haven't had it apart or drilled near it since like... 3 years ago when I was putting the dash together. If it's something I can take apart and get back together after cleaning, then maybe I try that.

 

Stupid question, what are the magnets for? Is it electronic inside?

As far as I know, most speedos work with magnets, that is why you can move the needle with your finger and not break it.

I put two diode lights in a speedo housing once, while drilling the holes the metal dust from the drilling went straight to the magnet, I had to make another speedo up, as I could not get the dust off the magnets, it showed 100mph at some ridiculously slow speed.

When the cable starts binding it makes the speedo jump up and down(fast/slow pulsing), that is what I thought you were talking about at first till I viewed the video. 

[josh817]

Well I guess that is good and bad. Sounds like the problem but if you were unable to fix yours even after cleaning then ruhroh...

Thank you for the information

[datzenmike]

The cable spins a magnet inside a metal drum with a return spring. The magnetism induces currents in the metal drum. They in turn, react with the magnetic field and are dragged around in the same direction. The faster the spinning, the farther it drags the drum around.

 

Internet beer or kudos to who can name the famous inventor of the speedometer.

[420n620]

Inventor Nikola Tesla received the first patent for a type of speedometer that was based on a rotating shaft-speed indicator in 1916. But Arthur P. Warner, the original founder of the many incarnations of Warner Electric, claims the rights to the first invention of a speedometer for the automobile. Warner Electric still services the automotive industry by providing industrial clutches and brakes, along with sensors, switches and tensioner systems.           

 

 

interesting fact/s

The first speedometers date back to man's early travels. Since man began adventuring and traveling, he's looked for and found ingenious ways to record his travel data. Wheel markings on chariots helped early Romans estimate travel distances and average speeds by counting the wheel revolutions. Chinese texts from the third century tell of a drumbeat that helped the Chinese determine traveling distances. Every time the gear train of the Chinese mechanism, driven by the wheel of the mechanical carriage, hit a specific mark after traveling a set distance, an arm would hit the drum face. Christopher Columbus had sailors use a knotted line with knots spaced evenly at specific intervals to help Columbus determine nautical speed -- thus the term "knots" when talking about boat speed. Sailors would drag the weighted, knotted line in water. Sailors counted the available knots let out in a set period to determine the ship's speed.

 

 

no need for net beer or kudos, just knowing is a good reward.

[josh817]

So I mean.......... How do I fix it. haha
 

I am acquiring a 620, if that's of any use as far as nabbing parts. Also considering selling the 521 for a 510 Wagon. Still very unsure!


I guess one way I could test your magnet theory is by measuring the odometer distance against real distance. If the gauge is readying 100 but the odometer still reads like I am doing 60, then according to this diagram that would mean the cable is fine and the magnet is funkafied since it reads the input, not the magnet.

 

If it reads just as fast as the gauge shows, then I guess that means a bad cable. I'm a little worried if the only solution is to buy another cluster. Can try to clean it but I bet I would mess up my odometer, and you said you didn't have any luck doing it. :poop: Poop. Wish I knew what made it mess up in the first place. I haven't touched anything around it, I can only imagine a bump shifted something.