CVT Gearbox Faults: Why They Whine, Shudder or Slip

Continuously variable transmissions, or CVTs, feel different from any other gearbox. There are no gear steps, just a smooth rise in revs as the car accelerates. When one starts to misbehave, that smoothness is the first thing to go.

Here is how a CVT works, what typically fails and how to approach a problem sensibly.

How does a CVT actually work?

Two cone-shaped pulleys are linked by a steel belt or chain. One pulley is connected to the engine side and the other to the wheels. Hydraulic pressure squeezes each pulley's cones closer together or lets them move apart, which changes the effective diameter the belt runs on and therefore the ratio.

Because the ratio can change continuously, the engine can stay at an efficient speed. The system depends heavily on correct fluid, correct pressure and clean, undamaged pulley surfaces, so problems in any of those show up quickly.

What are the symptoms of a failing CVT?

Symptoms vary between makes, and some behaviour is normal for the design, such as engine revs staying high while the car gathers speed. What is not normal is a change from how your own car used to feel.

• Whining or droning that gets worse over time
• Shudder or judder when pulling away
• Slipping, with revs rising but speed lagging
• Delay or hesitation when selecting drive
• Limp mode or a gearbox warning light
• Burning smell or fluid leaks

What causes CVT problems?

Fluid is central. CVTs need a specific fluid, and the wrong type, low level or old, worn fluid can cause slip, noise and heat damage. Contamination from metal particles worn from the belt or pulleys then accelerates the damage.

Other causes include a failing valve body or solenoid, a weak pump, sensor faults, overheating from towing or heavy loads and a damaged start-up clutch or torque converter. Frequent hot, hilly or stop-start use makes everything work harder, so check the fluid service interval your maker recommends.

Heat deserves a special mention. A CVT belt relies on friction against the pulley faces, and hot fluid loses its ability to protect them. Towing, long climbs and summer traffic all raise gearbox temperature, so a car used that way needs its fluid condition taken seriously.

Should you keep driving with a CVT fault?

A slight whine may allow short trips, but slipping and judder usually mean wear is progressing and the damage may be spreading to the pulleys. If drive is lost, the car will not move, or it slips badly on a hill or in traffic, stop in a safe place and do not keep driving.

We do not provide recovery, so a recovery provider would need to move the vehicle. Message us once it is safe and we can talk through what you have noticed.

What can be done to repair a CVT?

The answer depends on the diagnosis. Some faults are electronic or hydraulic and can be put right with sensor, solenoid or valve body work, with a fluid service where the maker allows it. Others involve internal wear needing gearbox removal and either repair or a replacement unit.

We do not promise a repair is possible before inspection, and cost depends on the vehicle, the parts and the extent of damage. A scan and road test come first so that money is spent in the right place.