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#4660844 - 02/09/18 10:54 AM School me on the DCT
andyd Offline


Registered: 09/25/04
Posts: 7139
Loc: Marshfield , MA
Ever since I first encountered the term dual clutch transmission I've wondered what was good about having 2 clutches? What makes a DCT work? . TIA
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#4660861 - 02/09/18 11:08 AM Re: School me on the DCT [Re: andyd]
Olas Offline


Registered: 12/11/13
Posts: 3933
Loc: Manchester, England
You know about input shaft/lay shaft/output shaft and the sliding mesh gears?
Well imagine two concentric input shafts, one has gears 1,3,5 other shaft has gears 2,4,6. Each shaft has its own clutch and can 'preselected' the next gear so it only has to change from one concentric input shaft to the next.

There's some cool animations on YouTube
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#4660866 - 02/09/18 11:10 AM Re: School me on the DCT [Re: andyd]
Olas Offline


Registered: 12/11/13
Posts: 3933
Loc: Manchester, England
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#4660903 - 02/09/18 11:46 AM Re: School me on the DCT [Re: andyd]
WyrTwister Offline


Registered: 01/13/13
Posts: 1506
Loc: Texas
I have read up on the problems with the Dual Clutch Transmissions on the Ford Escape and Focus .

Those transmissions give the appearance of an automatic , but are more a semi-automatic transmission under electronic control . Do not think they have the torque converter , like the traditional automatic . Maybe no planateraries or " wet clutches " .

This last summer when we were shopping for a used car , I ruled out the Focus because of the history of problems with the transmissions .

I think the Dual Clutch transmission is suspose to be more fuel efficent than the traditional automatic ?
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#4660912 - 02/09/18 11:58 AM Re: School me on the DCT [Re: WyrTwister]
supton Online   content


Registered: 11/09/08
Posts: 11925
Loc: NH
Originally Posted By: WyrTwister
I think the Dual Clutch transmission is suspose to be more fuel efficent than the traditional automatic ?


Yep. Never in a slippage region like an unlocked torque convertor. I think all the controls are electromechanical? conventional automatics use a fluid pump to generate pressure; but in order to have sufficient pressure at low engine rpm means it's bleeding lots of pressure off at high rpm. [Pump is driven off the engine, so that the transmission will work at idle.]

IIRC first & reverse are usually pretty low, so as to get around having to slip the clutch a lot.

It's a pretty cool idea. Just one that seems to have had a few teething issues--good idea, and some bad implementations it seems.
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#4660919 - 02/09/18 12:08 PM Re: School me on the DCT [Re: andyd]
Reddy45 Offline


Registered: 08/15/08
Posts: 2967
Loc: USA
I think the biggest problem with DCTs is that people get them and drive them like traditional automatics (with the same expectations).

A lot of the complaints probably have to do with how the DCT prepares the next gear. If you drive in a manner that is not consistent with how a DCT is programmed then you're going to think it's clunky and inefficient.

Burnt clutches would be another issue. The mfrs should only use wet clutch DCTs for consumer vehicles. This might give it a fighting chance to survive when the car is held up on a hill with just the gas pedal.

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#4660925 - 02/09/18 12:14 PM Re: School me on the DCT [Re: andyd]
andyd Offline


Registered: 09/25/04
Posts: 7139
Loc: Marshfield , MA
Thank you, Olas. I kept waiting for the the guy's beard to get caught in the gears. And DCT are "good" because they shift faster? Further wikipedia informs me that they are used in everything on wheels.
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1994 Ranger ,the Rat, 5w30 dino, STP filter

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#4660938 - 02/09/18 12:27 PM Re: School me on the DCT [Re: andyd]
JTK Offline


Registered: 08/14/03
Posts: 10559
Loc: Buffalo, NY
I think they've got some good things going for them, such as needing gear oil for a lube as opposed to expensive, unit-specific ATF/CVT fluid. Not a lot of heat generated, nor the need for fluid coolers/heaters either.

Like said, I think with the right driver and driving conditions, DCTs could be a great thing.


Edited by JTK (02/09/18 12:27 PM)
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#4661008 - 02/09/18 01:30 PM Re: School me on the DCT [Re: andyd]
rooflessVW Offline


Registered: 12/24/11
Posts: 4039
Loc: North Carolina
Which DCT doesn't need a special oil?
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#4661027 - 02/09/18 01:42 PM Re: School me on the DCT [Re: rooflessVW]
KrisZ Offline


Registered: 12/23/06
Posts: 7460
Loc: Toronto, Canada
Originally Posted By: rooflessVW
Which DCT doesn't need a special oil?


Dry clutch units should not need anything special.
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#4661048 - 02/09/18 02:07 PM Re: School me on the DCT [Re: KrisZ]
rooflessVW Offline


Registered: 12/24/11
Posts: 4039
Loc: North Carolina
Originally Posted By: KrisZ
Originally Posted By: rooflessVW
Which DCT doesn't need a special oil?

Dry clutch units should not need anything special.

And yet...

Porsche, BMW, VW, Audi, Ford, etc. all use special oils in their dual clutch gearboxes.
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#4661063 - 02/09/18 02:41 PM Re: School me on the DCT [Re: rooflessVW]
KrisZ Offline


Registered: 12/23/06
Posts: 7460
Loc: Toronto, Canada
Originally Posted By: rooflessVW
Originally Posted By: KrisZ
Originally Posted By: rooflessVW
Which DCT doesn't need a special oil?

Dry clutch units should not need anything special.

And yet...

Porsche, BMW, VW, Audi, Ford, etc. all use special oils in their dual clutch gearboxes.


I'm talking from a technical point of view, not marketing and revenue generation. If the clutches are dry, the only reason I can think of is some special and exotic materials used in synchros to cope with the computer controlled actuators. But I think it's a stretch.


Edited by KrisZ (02/09/18 02:41 PM)
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#4661064 - 02/09/18 02:42 PM Re: School me on the DCT [Re: andyd]
MolaKule Offline


Registered: 06/05/02
Posts: 19042
Loc: Iowegia - USA
Most DCT fluids are MTF-type formulations with an [email protected] viscosity.

https://www.youtube.com/watch?v=lFAtc-zOKZs


Edited by MolaKule (02/09/18 02:57 PM)

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#4661161 - 02/09/18 04:16 PM Re: School me on the DCT [Re: WyrTwister]
Danh Offline


Registered: 10/16/10
Posts: 1749
Loc: .
Originally Posted By: WyrTwister
I have read up on the problems with the Dual Clutch Transmissions on the Ford Escape and Focus .

Those transmissions give the appearance of an automatic , but are more a semi-automatic transmission under electronic control . Do not think they have the torque converter , like the traditional automatic . Maybe no planateraries or " wet clutches " .

This last summer when we were shopping for a used car , I ruled out the Focus because of the history of problems with the transmissions .

I think the Dual Clutch transmission is suspose to be more fuel efficent than the traditional automatic ?


The Escape has a conventional 6 speed automatic. DCTs are on the Focus and Fiesta.

There are DCTs and there are DCTs. The Focus/Fiesta version sold in the US is a dry-clutch unit designed for lower torque applications. This version is sold elsewhere too, but more common is a wet-clutch, high torque DCT mated to Diesel engines.

Fordís was and is a mess. First, itís a dry clutch that is inherently more challenging. Second, itís uncomfortably close to its torque capacity in the Focus. Third, Ford did an abysmal job of testing, Fourth, quality control over the gearbox and clutches was lousy. Having owned one and gone through 3 clutch packs and countless program updates over 45k, I can confidently advise people to stay away.

I now have an Acura with both wet clutches and a torque converter and itís great.

DCTs are more engaging to drive than a conventional automatic and can be more efficient. Properly designed, they can also be trouble free. But stay away from dry-clutch variants.

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#4661210 - 02/09/18 05:37 PM Re: School me on the DCT [Re: supton]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
Originally Posted By: supton
conventional automatics use a fluid pump to generate pressure; but in order to have sufficient pressure at low engine rpm means it's bleeding lots of pressure off at high rpm. [Pump is driven off the engine, so that the transmission will work at idle.


This is no longer true.

All modern auto transmissions vary pressure to the clutches depending on RPM & Load.

Under light cruise, very little hyd pressure is to the clutches.
Under heavy load and acceleration, the pressure increases to keep the clutches tight.
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