Pros and cons of buying a car with a CVT transmission
Why do car makers use continuously variable transmissions or CVTs? A vehicle with a conventional automatic transmission loses some of the momentum while the transmission is shifting between gears. The CVT technology is clever and simple. It has fewer moving parts and changes the gear ratio seamlessly with no interruptions. This improves fuel economy, although the effect is more noticeable in city driving.
What are the drawbacks? Is it good for towing or racing? What to watch out for when buying a used car with a CVT? Before we answer these questions, take a minute to read how the CVT works.
How does a CVT work?
Audi Variable Automatic Gearbox (CVT) See larger photo
We are only talking about the mechanical CVT with a variator; the eCVT used in the Prius and other hybrid vehicles is completely different.
The key component in this Audi CVT is the variator that consists of the chain running between two pulleys (some CVTs have a steel belt instead of a chain). Each pulley set is made of two cones facing each other. The working surface of the cones is smooth. The size of each pulley set can be changed by pushing the cones towards or away from each other using hydraulic pressure.
The engine runs the pulley set 1; the pulley set 2 is connected via the differential to the drive wheels. Right now the cones of the pulley set 1 are pulled away from each other, while the pulley set 2 is squeezed together. This equals to the low (1-st) gear in a regular transmission.
High and Low gear of the CVT transmission
As the vehicle accelerates, the transmission "upshifts" by gradually increasing the size of the pulley set 1 and reducing the size of the pulley set 2.
Can you guess the main drawback of the CVT looking at both diagrams? You are right, it's the limited torque. If the engine had too much torque, the steel belt or chain would slip on one of the pulleys. In a CVT transmission, slipping of the steel belt or chain causes the cone surfaces and the chain/belt edges to deteriorate. As a result, products of wear contaminate the transmission fluid.
Manufacturers are working on ways to increase the torque capacity of CVTs, but for now it's limited. For example, the major CVT producer Jatco lists in its product profile the torque capacity of the JF016E CVT at 250 Nm (184 ft-lb). This Jatco CVT unit has a steel belt and is used in some Nissan vehicles. The torque capacity of CVTs that use a chain is higher, but still limited. For example, the Audi CVT in the diagram above is rated at 280 Nm (207 lb-ft). That's the reason you don't see CVTs in pickup trucks or muscle cars, where the engine torque is much higher.
Another drawback is that CVT problems are expensive to repair, in part because the repair often involves replacing the valve body or the whole unit. The CVT unit replacement costs upwards of $4,000 in some cars.
Can a CVT transmission be used in high-performance cars? Nissan uses the CVTs in most of its lineup, but the 370Z offers a conventional 7-speed automatic and the GT-R has a 6-speed double clutch automatic. Subaru, though, was able to fit the CVT in the WRX. Is it better than a manual? Read this article by Car and Driver.
The CVT works well in small and medium cars and SUVs. Manufacturers program CVTs to keep the engine revving higher on acceleration to reduce the load on the CVT variator. That's why many reviewers often mention a louder engine noise and slower acceleration of the CVTs.
Because of its design, CVTs are better suited for fuel-efficient city driving and moderate load. If you need a car for long daily highway commutes, towing or sporty driving, a conventional automatic or a manual transmission will do better in our opinion. CVTs and other automatic transmissions are also sensitive to overheating.
What to watch out for when buying a used car with a CVT
The first question should be about the warranty, because as we mentioned, the CVT transmission repair is expensive.
What are the early signs of CVT problems:
1. Delayed engagement: when you shift from Park into Drive or Reverse and it takes more than a second or two for the transmission to engage.
2. Abnormal noises (usually humming or whining): in some cars, they are more noticeable on acceleration, in others on deceleration or coasting.
3. Loss of power on acceleration, slipping.
4. Shudder, jerks or jolts when shifting into Drive or Reverse or when driving.
5. Fluctuating engine rpms when driving at a steady speed.
6. Dirty transmission fluid.
Many owners who experienced CVT problems mention that they appear after the vehicle has been driven for a while and the transmission is fully warmed up. Read more: How to inspect a used car, guide with photos.
Check these Youtube videos for more tips on how to recognize CVT problems.
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