How a Dual Clutch Transmission Works

Here is a look at what’s inside a dual clutch automatic transmission and how it works!

A dual clutch transmission is internally very similar to a manual transmission – with the exception that the computer (mechatronic unit) is responsible for physically shifting the gears. Instead of a single dry clutch like in a manual transmission, a DCT uses two wet clutches, one larger than the other one to drive two input shafts to the transmission. The two input shafts will power either the even gears or odd gears.

Other accessories to the transmission include a transmission cooler, oil filter and oil pump that serves to cool and lubricate gears and bearings. The transmission computer is located inside the transmission mechatronic unit, which control solenoids to redirect fluid flow through a valve body. The valve body will in turn feed transmission fluid through the housing and into the pistons which will control the position of the selector forks and thus select the gear.

One advantage of a DCT is that it can shift gears much faster by preselecting the next gear that the computer thinks it will shift to. It does this by engaging the fork of the opposing gear that is currently being used. The downside is that it can often get confused if the driver has erratic inputs and therefore cause hesitation or jerky output.

Finally, while the wet clutch and gear synchronizers are often wear points on these transmissions, the mechatronic unit is often the fault for many failures.

The transmission in this video is a DSG (direct shift gearbox) D250 unit from a 2006 Volkswagen Jetta TDI.

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[jessicaandtrains]

I often watch videos at 1.75x speed but yours I was able to watch at 1x. Great editing and no time wasting 👍

[prveteran]

I still continue to be highly impressed with your knowledge on cars. You're like a neurosurgeon working on cars. UNBELIEVABLE. Like a walking encyclopedia. Good for you!

[dehypnotizer]

Great vid, as usual. Those clutch pads are in mint condition given the fact that the vehicle drove over 300 kkm. Looks to me like a great piece of engineering.

[borntojoke]

As a junior (thermal/aero) enginner in the automotive, I consider these videos pure GOLD! You would not believe how much stuff we learn in school, and even on the job, but especially now with electric vehicles everyone specialises on just a tiny parts/systems of the car. Seeing this stuff is so interesting, and it allows through your eyes and experience to have the general view of all the systems! Plus now, a lot of these mechanical parts will be gone with EV, so I try to learn what I can before they disappear completely! Thank you!

[michaelbezoski]

Literally blown away. The machining to make it all work is only matched by your explanation. Thanks for all the effort to teach me why bicycles still have a place in this world (maybe horses too). Your #1. Still do not understand how you can sit cross legged based on the Mrs. cooking. You two are real stars of youtube!

[arctus]

Wanted a DCT video for a while now. Great video as always.

[Erik_Swiger]

That bit you said about the transmission becoming "confused." This is exactly the problem I have with modern car technology. The transmission itself is fascinating, and in theory, a great idea. But making it so complex that it cannot function, is a bad idea. I can't imagine a Turbo-Hydramatic becoming "confused." Great video, and as always, I love your choice of rags to clean up with.

[thatguy]

Wow I can’t lie I was expecting all the parts to be worn and in poor condition, glad to see VW manufactured a (mechanically) reliable unit.

[mscir]

GREAT video, I had no idea how these worked. The condition of the clutch disks is amazing. Great design. Thank you.

[keremardicli]

These are very valuable spare parts. Hope they get to work again some day.

[kylevarble]

Absolutely love your videos very educational and hilarious I appreciate all you do. Watching your videos is so easy because your not afraid to show your process of figuring it out when others cut that out and try to look like they know it all and don't make mistakes. Keep it up I look forward to all your videos

[martynjames]

Great video. Understood everything ...except ... how could anyone invent this!!! Pure genius. Nobel prize material!

[TimmieTennis]

Love the toothbrush… this some of the best content on YouTube!

[doctorrobert]

While looking very complex amazing it works as seamless as it does. Been driving manual transmission cars for long time but recently purchased a 2022 VW Arteon that has the wet clutch 7 speed DSG. Hope it is as dependable as standard manual transmission. Thanks for posting the interesting and elucidating video!

[milesredgate]

Transmission's always make my brain hurt, but I think this is the first time I feel like I've understood something about their mechanicals.

[tristanv]

I will most definitely be referencing this video when I argue with the dealer about how fucked my transmission really is. I got a warranty specifically for my transmission (I’ve had terrible luck with them in the past) and they’re replacing small relatively insignificant parts bit by bit as if shifting isn’t rough throughout all gears. I appreciate you sir

[dgurevich]

The complexity of this gearbox is mindboggling.
No wonder nobody wants to touch these.
I had the un-pleasure of driving a car with single clutch robotic, and if this one shifts as slow as the one I had (the actual movement of the forks, not the clutch engagement), no wonder the internals are that well preserved.

[nickchannel]

He has a dry sense of humor. Love it.

[Greebstreebling]

Ah, the dreaded oil pump drive. It broke on my wife's 2008 Passat, a common major failure which VW wouldn't acknowledge. I had bought VWs all my life until that event, but VW just threw us in the ditch, customer loyalty meant nothing, so I now have a nice Volvo. Nice to see the gearbox tear down, makes you realise how much things have moved on since the days of the Morris Minor with no synchro on 1st gear....Thanks for posting, love the high speed explanation of dual clutch transmission, the concentric clutches seems a nice idea.

[alexs.]

The guy I bought my car from said his family owned a VW with a DSG, and they sold it with close to 200k miles with the original DSG still working well. He said they maintained it with regular fluid and filter changes. MAINTENANCE IS KEY!