Needle bounces or jumps around

Most common of all, and usually the cheapest to fix. If the needle flutters or leaps — especially below about 30–40 mph, smoothing out at higher speed — the cause is almost always a dry or binding cable. The inner cable snags inside its housing, winds up like a torsion bar, then releases: bind, snap forward, bind again. That stutter is what you see at the needle.

If a freshly lubricated, undamaged cable still bounces, the fault has moved into the gauge head.

Whirring, squealing, ticking or grinding noise

A dry cable is a noisy cable. The same friction that causes bounce causes sound. Long cables, tight bends and kinks all make "whip" worse — keep the run as short as sensibly possible and free of sharp angles. Clean and lubricate as above. If the noise is a rhythmic tick tied to road speed, also check for a frayed strand catching or a worn drive gear at the transmission end.

Needle sticks, reads zero, sits low, or only works when you tap it

When the cable clearly spins but the needle is lazy, stuck, wanders, or springs to life after a tap on the glass, the problem is inside the gauge head. After decades the factory grease on the magnet spindle turns to a waxy varnish, pivots wear, and the hairspring weakens. Symptoms include a needle that hangs, reads consistently low, swings wildly, or vibrates.

This is not a driveway job. It calls for a bench rebuild: full disassembly, cleaning off the old grease, servicing the magnet, speed cup and pivots, replacing the hairspring if needed, and — critically — recalibrating on a machine. See what a professional rebuild involves or go straight to the shop directory.

Odometer is stuck, skipping, or the trip won't reset

The odometer runs off the same shaft through a fragile gear train. Gummed grease, a slipped worm gear, or a cracked plastic number-wheel gear will freeze the count or make it jump. Because the numbers are geared, one bad tooth can stop the whole train. This is gauge-head work, done during the same rebuild that services the speedometer — and a reputable shop returns the unit with your original recorded mileage preserved.

Speed reads consistently too high or too low

If the needle is steady but simply wrong — reading, say, 70 when you're doing 60 — the mechanism is probably fine and the calibration is off. The usual trigger is a driveline change: new tyre diameter, a different rear-axle ratio, or a transmission swap. The fix is the correct driven gear at the transmission for your combination, and/or bench recalibration to the right turns-per-mile. Many gauge shops will recalibrate a unit to a spec you provide.

Speedometer completely dead, cable spins

If nothing moves at all, work from cheap to expensive: a snapped inner cable (a common failure — the squared tip shears off), a stripped plastic drive/driven gear at the transmission, or a seized gauge head. Corvette and many classics have inexpensive cable repair kits for a broken tip; a seized head goes to a shop.