CVT — Belt and Pulleys
CVT — Continuously Variable Transmission
A CVT does not shift between fixed gear ratios like a conventional automatic. Instead, it varies the ratio continuously and seamlessly. There are no gears, no shift points, no steps. The engine RPM rises to an efficient point and holds there while the vehicle accelerates smoothly. This makes a CVT extremely fuel efficient but gives it a different feel that some drivers describe as the engine droning or the transmission slipping. It is not slipping — that is how a CVT is supposed to feel.
How it works — the pulley system
A CVT uses two pulleys connected by a steel belt or chain. Each pulley has two cone-shaped halves that can move closer together or farther apart. When the halves are close together, the belt rides high on the pulley — large effective diameter. When the halves spread apart, the belt drops to a smaller diameter. The drive pulley connects to the engine. The driven pulley connects to the output. By changing the effective diameter of both pulleys simultaneously, the CVT changes the ratio. Small drive pulley plus large driven pulley equals a low ratio for starting out — like first gear. Large drive pulley plus small driven pulley equals a high ratio for highway cruising — like top gear. And everything in between, continuously, with no steps.
Belt vs chain
Some CVTs use a steel push belt — hundreds of thin steel segments strung on steel bands that push against the pulley faces. Others use a chain with pins that contact the pulley faces. Chain CVTs can typically handle more torque and are used in larger vehicles. Both types rely on friction between the belt or chain and the polished pulley faces to transmit power. This is why CVT fluid is absolutely critical — it must provide exactly the right friction coefficient. Too slippery and the belt slips on the pulleys. Too grabby and the pulleys cannot adjust smoothly.
CVT FLUID IS NOT ATF. It is a completely different formulation. Using standard automatic transmission fluid in a CVT causes immediate damage to the belt and pulley surfaces that may not be obvious at first. The belt and pulleys are being destroyed with every mile while the vehicle seems to drive normally. By the time symptoms appear, the damage is catastrophic and the CVT needs replacement. Always verify the exact CVT fluid specification from manufacturer data before any service. There is no universal substitute.
Common CVT problems
Shudder or hesitation during acceleration from a stop — often a fluid condition issue that resolves with a drain and fill using the correct fluid. A droning or vibration at steady speed — belt or chain wear. A sudden loss of drive or a feeling of slipping under hard acceleration — the belt is slipping on the pulleys due to worn pulley surfaces, incorrect fluid, or low fluid level. CVTs are not rebuildable in most general repair shops — they require specialized tools and components. Most failed CVTs are replaced as a complete unit.