One mechanism, many badges
GM standardised its cable-driven, AC-Delco instrument design across divisions, so parts knowledge and service overlap heavily with Chevrolet. A Skylark, Cutlass, GTO, LeSabre or Cadillac speedometer uses the same magnet, speed cup, hairspring and odometer train — and shows the same age-related faults.
The usual faults
Low-speed bounce is a dry cable — clean and lubricate first. A stuck, lazy or dead needle with a good cable is hardened grease or worn pivots in the head, needing a bench rebuild and recalibration. A frozen odometer is gummed or stripped number-wheel gears, serviced in the same rebuild.
G-body squeak (1978–1988)
Later rear-drive GM G-bodies are known for a squeaky, bouncing cable at low speed — the same dry-cable story. Fit the shortest sensible cable, avoid kinks and sharp bends, and use graphite or a PTFE dry lube rather than grease.
Recalibration after driveline changes
Swapped the rear gears, added taller tyres, or changed transmissions? The reading will be off until the driven gear matches the new combination or the gauge is recalibrated to the correct turns-per-mile.