I would suspect a faulty VSS. Try replacing the vehicle speed sensor in the transmission.
If it's an electronic (analog) speedometer needle, you probably have a problem with the dasboard grounding.
Possibly your speed sensor. My speedometer would bounce around & then soon after it felt like my transmission was slipping. Turns out the speed sensor controls the upshift in your transmission.
Lowering the springs of a car will cause the tires to bounce.
So the speed gauge in the dash and the speedometer cable have been replaced. Well, the only thing left to my knowledge would be the geared speed sensor in the transaxle. I have the same problem. Replaced the speedometer cable but to no avail. I then took the speedometer out and used an electric motor to drive it on my bench and noticed that the part that is driving the needle (driven by a magnet) starts vibrating at certain speeds. On further investigation I found that the bush on the panel that the spindle goes through ( just behind the needle) is worn and hence the spindle/shaft does not run tight and starts vibrating/rattling and then it sometimes swing up and down. When I lightly touch the needle it stabilizes for a while and then starts vibrating again. The needle is not driven directly, but through a magnetic coupling so the slightest interference can cause problems. It seems the only solution is to replace the speedometer. Unfortunately you have to replace the whole cluster. I thought I could do something about the bush, but it is too delicate and you will have to remove the little coil spring which means the speedometer will have to be re-calibrated.
There are several things that can cause your 2003 Mitsubishi Gallant speedometer not to work. The most common cause is a malfunctioning speedometer cable.
You may need to replace the speedometer fuse. The speedometer cable can cause your speedometer to stop working. The speed sensor can also cause the speedometer to stop working.
The speed sensor is malfunctioning If the speedometer is still run by a cable from the transmission, the cable could be getting bound up inside the case that covers it. With heat and time the lubricant inside the plastic tube and that covers the metal cable gets dry and hard and sticky. As the cable begins to twist it will spin and then catch and then release causing the needle to bounce. This is only if you have what I consider to be a mechanicaly fed speedometer. If it is electronically fed with a speed sensor and all, answer ! may be correct. I owned a 95 and thought for sure I had mechanically activated speedometer. And on a side note if it is not the cable itself, then it may be the speedometer gear in the tranny going bad. As the tranmission speedometer gear rotates it spins the cable inside the plastic tube. Possibly a tooth or two broke off. If you find your speedo is run by a cable, there are ways to lubricate them if you can get it disassembled from the rear of the speedo or from the tranny. You may want to look at purchasing a new cable and just replacing it that is if you have a cable fed speedometer.
There are several things that can cause your speedometer to stop working. The most common cause is a blown fuse. The second most common cause is a malfunctioning speedometer cable.
Either the cable dry or something is wrong in the head. Take the cable out first and lube it and see if that fixes it.
sounds like a broken speedometer cable.
the speed sensor, trans. sensor , or the speedometer cable
The rear axle speed sensor is the usual cause of an inoperative speedometer.