What Causes the Speedometer Needle to Shake?
2 Answers
The reason for the up-and-down shaking of the speedometer needle is due to a malfunction in the vehicle's oxygen sensor. It is necessary to promptly visit the car's 4S store or a repair shop to inspect or replace the oxygen sensor to resolve the issue of the tachometer needle shaking. How the Speedometer Works: When the car is in motion, the drive shaft rotates the permanent magnet. The magnetic field lines of the permanent magnet generate eddy currents on the aluminum cup. The interaction between these eddy currents and the magnetic field of the permanent magnet creates torque that overcomes the spring force of the spiral spring, causing the aluminum cup to rotate the pointer by a certain angle. Types of Speedometers: Common vehicle speedometers are generally divided into three types: purely mechanical, mechanical-electronic, and purely electronic. Among these, purely mechanical speedometers have largely exited the market, mechanical-electronic speedometers are the most widely used, and purely electronic speedometers are typically employed in the bus industry. Function of the Car Speedometer: The car speedometer displays the vehicle's speed changes, including the instantaneous speed, engine RPM, and accumulated mileage. The driving speed is usually indicated by a pointer that continuously changes while driving. Other information is typically displayed using rolling numbers similar to those on an electric meter.
I've been driving for over 30 years and have seen many cases of speedometer needle fluctuations in older cars. Most often, it's caused by wheel imbalance—either uneven tire wear over time or improper wheel balancing. At high speeds, the wheel wobbles severely, causing unstable speed signals that make the needle jump. It could also be due to dust buildup or jamming in the speed sensor, leading to intermittent data transmission. Another possibility is aging or loose wiring, where corroded connectors interfere with the signal. Sometimes, transmission issues can also affect speed readings. This isn't a minor problem—misjudging speed due to fluctuations can easily lead to speeding-related accidents. I recommend getting your tire pressure and sensors checked at a repair shop first; it's an affordable fix (usually just a few dozen bucks) and shouldn't be delayed. Safety comes first—drive with peace of mind.
