We had a gorgeous summer day yesterday, so I got my old Austin gasser out of it's winter nap and took it for a drive. I barely got down the road when I heard a loud screeching noise! I slowed down and the noise lowered, sped up and the noise got louder. I happened to look at my speedometer and at maybe 30 mph it was reading 45 mph! I sped up to 35 mph and the noise increased, and speedo read 60 mph! I figured it was the speedo cable as I didn't hear noise from the dash or speedometer. Turned onto the freeway ramp to see what it did at freeway speed and at around 55 mph it read 110 mph! Driving down to the next exit it suddenly got quiet, and the speed read 55 mph and seemed to be fine. Local street speeds on the way home all went fine, and not more noise or speedo erratic readings. I guess the cable was dry and finally smoothed out. I stopped by the chain store and ordered in a new cable. I know zip about how speedometers, or drive cables work, but why would a sticky or maybe rusty cable make the speedometer read almost double your car's speed?
You can remove the center core of the cable, from the top, and clean and grease it. Then see if it's fixed. But it's pretty common for speedometers to give you a hint that they're about to fail, and what you saw was that hint. If the cable lubrication does not fix the issue, send the speedometer off to Rusty for an overhaul.... I've had this very same experience with speedometers in at least 3 LeMons Rally cars. It sucks when it happens on a road trip, and the only solution is to disconnect the speedometer.
My self I use the steel outer cable , When New I coil up & use a drill to spin inner to wear fit to each other Then remover inner , clean both I & O, After cleaning , Lube & install
Noise and/or reading faster is usually a sign the inner cable is sticking somewhere in the casing. The inner cable winds up and releases, spinning faster, sometimes slapping against the outer casing and making weird noises when it overcomes the friction. It will eventually break if not cleaned and lubed.
X2 on the speedometer head is about to go out. If you keep driving it you will ruin the speedometer and it will cost more to fix it. Just had the same exact thing happen to the tach on my 56 T-Bird. Rusty fixed me up.
Picking up the whole new cable in a little while, but also going to pull the inner cable first just to see what it looks like, and whether I see any strange signs of wear on it. The catching and winding up makes sense why it read so much higher.
The other thing that happens (I think) is that the jewel bearing in the speedometer itself gets worn, and the cup and magnet make contact with each other. Lubricating the cable might fix it, but it might not. Good luck
My 57 was doing that, it wasn't the cable but the speedo itself. The 57 speedo has a little sponge bit that holds oil, accessible by pulling out a tiny plug. That was dry on mine. Have to pull the speedo and partially disassemble it to get to it. If your car has the same, definitely needs to be reoiled.
These little plugs are on most old speedo's. Pick/pry them out using something with a sharp point or a new stanley blade. Don,t stab yourself . Then pick out the little sponge with a needle . Few drops of sewing machine oil to speed up the lubrication or WD40 if speedo is stuck solid. Once everything spins clean up excess oil with a cotton bud. Cotton bud can also wipe the numbers clean. spong in with a extra drop and then little plug in.
My speedo was new back in 2011 when I bought it, so I hope that's not the issue. Can't imagine it went bad in 14 years with a little over 20,000 miles on it.
Well no lubricating the old speedo cable! The inner cable was stuck good, and once I pulled it out it looked perfect. But checking the outer sheath I found one area where it was 2" above the exhaust and melted! So I cut it off and took the rest of it off. I routed the new speedo cable below the exhaust so heat rising wont affect it.
I had a couple of stock speedometers that sounded and read like the OP. I ended up lubing the speedo head like this with 3 in 1 oil to fix it.......after I checked the cable first.
I knew the sheath was damaged somewhere when it took pliers to pull the cable out of the sheath. After that it was just checking the length to see where. The sheath was a good 2" away from the exhaust, but above it, and only 6" past the collector on my fenderwell headers. So probably too much heat being above the exhaust. It's 2" below now, so hoping below isn't as hot as above. Everything is tight on the little car, so not much room for clearance. But I do have some 2" wide black exhaust wrap leftover from my '39 Chev build, and I think I'll wrap the speedometer cable with that to make sure it's shielded.
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