Elements of irrelevant tech are much like animals in a zoo, interesting to look at but, for the most part, not very good pets if you have to live with them. Every once in a while one of the animals escapes into the general population. A case in point is the dual clutch transmission. These started appearing in production cars about 15 years ago although they have a longer history in various prototypes, specialty sports cars, and Porsche Le Mans cars. Prior to that, the two standard choices for consumer car transmissions were manual (stick shift) or conventional automatic. Manual transmissions are simple, rugged, and efficient but not for everyone. Modern conventional automatic transmissions are the result of 90 years of refinement. They routinely provide reliable, quiet performance far in excess of 100,000 miles.
The dual clutch “automatic” transmission is very complex with a large number of moving parts, many more than a conventional transmission. It is effectively two manual transmissions, one (as an example) for 1st, 3rd, 5th, and 7th gear and the other for reverse, 2nd, 4th, and 6th gear. It has two clutches to switch the engine torque between the two gear trains, two counter shafts, and two sets of synchronizers. It contains multiple electric motors, reduction gears, and actuators to activate the two clutches and the shift forks for the various gears on each side and a computer to run the whole thing. This tends to make them fairly expensive.
The two sides take turns as the transmission is shifted between gears. As an illustration of normal operation assume the transmission has just up shifted to 3rd with the odd side now driving. The disengaged even side is in 2nd and will be moved to 4th to get ready for the next shift. To make that shift, the odd side clutch is disengaged and the even side clutch is carefully engaged to supply power in 4th gear. Note that there is no fluid coupling or torque converter as in a conventional automatic transmission so the clutch engagement must be handled as carefully and smoothly as with the clutch on a manual transmission to avoid jerks. One problem here is that the transmission has to guess which gear you will need next. For a straight acceleration up through the gears, or for a normal downshift pattern coming to a stop, this is not a problem. However, if you slowed down for a turn and want to speed up again, the off side transmission will find itself in the wrong gear and will have to shift back internally before it can transfer between the two clutches to apply power in the proper gear. On paddle shift versions this means that sometimes the dual clutch transmission shifts when you hit the paddle and sometimes it shifts later.
When a new tuned and adjusted dual clutch transmission leaves the factory it shifts as smoothly and as quietly as a conventional automatic. As it is driven, all the electric motors, reduction gears, actuators, bearings, and clutches start to wear. After a few thousand miles the transmission develops a slight whir with sliding noises when it shifts, especially during turns in traffic. When you take it to the dealer they will tell you there is nothing wrong with it as they are all like that. The reason the dealer tells you that is that they are all like that. After a few more thousand miles the whir turns into a whine of electric motor gears and the sliding noise turns into the shift forks clanking. Once again the dealer assures you that they are all like that. They offer to upgrade the software in the transmission, which doesn’t appear to do anything. After a few more thousand miles the actuators are worn enough, and there is so much slop in the linkages, that the clutches can no longer be operated smoothly, so the car jerks and shudders when pulling away from a stop. This was not a problem for the Porsche 956 Le Mans car, but it only had to run for 24 hours.
The dual clutch transmission is irrelevant tech.