Here’s the latest reader question, along with my reply!
Bobby asks: I’ve been looking at new cars, casually – and have noticed that probably half of them come with a CVT automatic. I’ve read and heard that these transmissions have problems, or are more prone to problems, than regular automatics. What are your thoughts?
My reply: Continuously variable (CVT) automatics have, indeed, become very popular – chiefly because they enable a given car to achieve slightly higher gas mileage vs. the same car with a conventional automatic. This 2-3 MPG difference (on average) isn’t much and probably not something most buyers would care about, either way – but it matters very much to the car companies, who have to comply with constantly upticking federal fuel economy fatwas.
CVTs are more efficient because they have, effectively, infinite gearing – as opposed to the fixed 5-6 (or 8-9-10) ratios in a typical automatic. They are able to get the engine RPM at exactly the right spot (or closer to the right spot) in its powerband for a given load/road speed.
The downside is that under full-throttle acceleration, they will let the engine rev to its power peak, which is usually high RPM – and hold the engine at that RPM until the driver lets off the pressure on the accelerator pedal. A conventional geared automatic will reduce engine RPM as the transmission shifts up through its gears. So, the CVT will often increase drivetrain noise and give the impression that the engine is working harder.
The other issue is that the bands which transmit the power (in between a pair of pulleys; this is how the ratio is continuously and infinitely varied) tend to be a weak spot and when they go, the transmission is often gone with it.
Regular (geared) automatics seem to be able to handle more power – and are more long-term durable.
Which is why I personally would avoid a CVT, if I were car shopping.
. . .
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Why are the bands so hard to replace on a car’s CVT? I have CVTs on my scooters, and replacing them is an easy, quick job.
Hi Mark,
I’ve heard (Brent will hopefully chime in) that what happens is the bands come apart and lots of small metal fragments then circulate throughout the tranny, effectively destroying it. My understanding is that most are not serviceable; you remove and replace with a new one.
Then it’s totally different than a CVT in a scooter. There’s a big, rubber belt between the variable pulleys, and all you do is swap out the belt. You undo the nut on the variator (the front pulley, so you can take the belt out. Then, you can pops off the back pulley, which is connected to the final drive. You then put the new one on over the back pulley, stuff it down, then put it on the variator. You tighten up the variator, and you’re done. I thought that the CVTs on cars worked in a similar manner, only with a bigger belt.
They are metal bands in an automotive CVT and when they come part it looks like some sort of clockwork decided to come unwound and unglued inside its case.
I think I found the videos I watched some time ago:
https://www.youtube.com/watch?v=T7Hhxrk9D3I
https://www.youtube.com/watch?v=_64zEsMdQ9A