There are three types of automatic transmissions available in todays cars.
Conventional one with a torque converter that everyone is familiar with.
CVT, Continuously variable transmission that has been slowly being used in more and more cars especially Japanese makes.
Dual clutch automatic, which is similar to a manual transmission except with two gear sets and clutches that shift automatically. Was available only on exotic cars with paddle shifter, but one has been made for small economy cars, that is in Fords Focus, and Fiesta, and is also available in the Dodge Dart.
In addition to the well-publicized problems that Ford is having with their dual-clutch units, many other makes of cars with similar transmissions suffer from very abrupt/rough gear changes, particularly at low speeds. In the Smart car (designed by Mercedes!), the gear changes are so pronounced that the driver and passenger frequently feel as if they are being pitched forward and back in their seats when the trans changes gears. And, there are other makes with similar dual-clutch-related problems…
The currently un-repairable nature of CVTs would keep me away from them.
Plus, it is not unusual to have a higher noise level in the passenger cabin with a CVT, due to both higher engine revs and whining noises from the trans.
jury is still out on the CVT. @Docnick
I made a similar statement some time ago, that the CVT would be ready for prime time when Ford, Honda and Toyota started to use them in their important models. I was not ready either then until that happened. Well, the Accord has one and the Corolla has one. In low load applications, they are ready.
As far as “un-repairable” is concerned, have you seem many dealers repair any transmissions of ANY type under warranty. The entire auto industry is moving to replace, not repair most of their components. The potential is for greater reliability, the life of the car according to Subaru, because of fewer moving parts. Don’t be any more afraid of a CVT then a complicated 7 speed auto on the market today. Do you think “joe blow independent” will dive into one of those ? Not likely.
NOPE ! You are pretty much in the same boat with most all autos.
Buy from a reliable brand with a history of reliable drive train components…and worry no more then you would about how anything was made. We had this same fear about hybrids…but Toyota hybrids are bullet proof ! I would not be ready to buy one from Audi, Volvo or Chrysler or etc…yet. But i wouldn’t even buy a gear auto transmission from them…yet, either.
@dagosa makes some great points, if you have a problem with your modern dual/clutch transmission or most conventional Automatics, the dealer will replace the whole unit since they aren’t allowed to tear the transmission apart. A ZF 8Spd transmission is just as likely to be replaced as a unit than any CVT or dual clutch.
Honda has offered a CVT on the civic since the late 90’s, Nissan hasn’t had such good luck. Some brands have more reliable mechanical parts than others. Dual Clutch gearboxes are another fairly recent idea for mass market, some are much easier to live with than others.
I’d say there are as many as six kinds of automatics.
In addition to the three named above, the there is the ‘CVT’ as used in the Prius and other hybrids using the same technology. It in no way resembles a CVT as used in other cars, but instead has multiple motors connected to planetary gearsets. The motors can acts as motors or generators, and in some modes one is doing one and the other the opposite. It has the advantage of great mechanical simplicity and reliability, but needs those two motor/generators and some complex control software/hardware. A very neat design that is surprisingly old in concept.
There are still a handful of high end sports cars using automated manuals with a single clutch. Some of the these can shift incredibly quickly, but it’s a brutally abrupt shift compared to what’s possible with a dual-clutch design. Some drivers of exotic sports cars want to feel like Formula 1 drivers, and those transmissions let them do it. That’s about their only advantage.
And finally, ‘conventional’ CVTs have been made with two different basic designs. The more common uses a V-shaped chain/belt (really more of a chain, but it seems more like a belt) running between two wheels of variable diameter (split halves that are moved relative to each other.) I don’t know if the other kind is being used in any current models but it has in the past. It has a disk (or disks) that rides under pressure between two complexly shaped wheels. The disk can be tilted so its edge turns against each wheel closer to its edge or nearer the center, changing the gear ratio. Both designs use some power to force the belt/wheel against the pulleys/wheels, but they are comparatively simple and compact and can have a wide spread of gear ratios. As the belt/pulley design seems to be winning out I’m guessing it has some advantage.
I suspect the CVT will continue to improve in durability and/or serviceability. There aren’t a whole lot of moving parts in them compared to a dual-clutch design and designing a . The ‘motor boating’ effect people dislike where engine speed is sometimes acting opposite vehicle speed can be avoided with a bit of programming or people will just get used to it. The current stair-step rising and falling as you accelerate is no more natural, just familiar. Engines have gotten so quiet I’ve had to point out to my partner when we’re driving a rental with a CVT.
Any transmission is only a part of the entire drivetrain. Which is “best” is totally dependent upon the vehicle in which they’re installed. The manufacturers focus enormous resources in powertrain development, and I’d trust them to pick use best design for the application.
In my limited experience with a couple of family members and friends who own CVTs, the high revving, noisy sound usually emanates from motors that are high revving to get much power and noisy doing it. The complaint on Subbie CVTs, can be lodged against Subbie manuals when they are revved. The Accord CVT seems pretty quite due to good engineering and a great motor to start with.
It’s extremely common, and even expected, for modern conventional automatics to last the life of the car. CVT trannys haven’t been around in volume long enough for me to have developed a sense of confidence in their long term reliability. But I’ll also admit that I’m not an “early adopter” of new technologies. I’ll steer away from CVTs for a while. It’s too early yet.
Traditional automatics are smooth because there is a fluid coupling to hide much of the shift shock. It is proven technology. However, it is the most inefficient of all because the torque converter slips all the time in low gears. The engine has to speed up before the transmission catches up. They also require hydraulic pressure to stay in gear.
CVT is the smoothest because there’s no gaps between ratio. They are theoretically the most efficient as they can keep the engine in the most efficient speed. In reality, they are equal to manuals in terms of efficiency as they have to use some of the engine’s power to keep a tight grip on the belt or chain. Also, since the belt or chain is not an infinitesimal element, it has to slip as it dive into or out of the cones. This slip is a source of wear and is a deal breaker for me.
Dual clutch manuals is nearly the most efficient type of automatics, second only to single clutch automated manuals. AMT can potentially be lighter than a traditional manual since it is electronically controlled and doesn’t need to have oversized components that can survive driver abuse. With a clutch transmitting engine power rather than a slipping torque converter, there is no waiting for the transmission to catch up the engine. The throttle response is immediate as it would be in a traditional manual. The downside is any rough throttle input is felt, whereas a traditional automatic would hide them. I personally would choose a single clutch AMT over a dual clutch because a dual clutch still use some engine power to keep one clutch engaged, unnecessarily wasting a small fraction of power.
A note on repairs: if you wear out the internal clutches in a traditional automatic or CVT, the transmission is sent to a specialist to be torn apart. Wear out the clutch on a manual, traditional or automated, the clutch job is significantly less invasive