6 ms·

Dual-Clutch Transmission: Wet or Dry?

35 points by luu 3y ago

datavirtue 3y ago
Wet. Dry have issues due to heat management and failing seals that end up slathering the clutch in lubricants. It boggles my mind that an engineer would choose dry. I think the idea was to reduce costs. In Ford's case it resulted in a fairly nasty class action law suit.
- HPsquared 3y ago
  Wet clutch has the problem of friction material building up in the fluid, which can cause wear and deteriorate the other components. Dry clutch is more modular, the clutch is more self-contained and seems like it would be better for long-term serviceability: if the clutch wears out, you can just replace that part.
  - rozap 3y ago
    Hm thanks for reminding me that I need to change the fluid in my DSG. It's annoying that the VW manual suggests comically long service intervals for this stuff to make it look like the running costs are lower than they are. I want to just keep the car until it has 300k+ miles. But it's all about shifting those units initially.
  - kube-system 3y ago
    I've always wondered if it would be able to build a car transmission with a clutch similar to a motorcycle. Those are very easy to replace.
  - bri3d 3y ago
    Concentric-shaft wet DCTs aren't bad - for example, replacing the clutch pack on a VW DQ250 is very similar to replacing the torque converter on an automatic. You have to drain it but it's not particularly involved. There's basically a cover on the bell housing behind the flywheel, drain the fluid, remove the snap ring, and you're looking at the clutch pack. Lift it off and lift a new one back on. Rebuilding the clutch packs themselves is a tedious and obnoxious process, because they're a giant stack of friction material that needs to be shimmed into tolerance, but you often just buy the clutch pack as a whole assembly. I'd massively prefer a wet clutch even for long term serviceability - a few hundred dollars or less every year or two for fresh fluid and you've got a long service life before an expensive removal.
  - IgorPartola 3y ago
    Wet clutches are standard in motorcycles. Lower power of course but they work very well across the entire segment.
    - fragmede 3y ago
      except for Ducati, famously
      - queuebert 3y ago
        But aren't they meant to be rebuilt every 10k miles or so?
        IgorPartola 3y ago
        Don’t know about Ducati but on other bikes a clutch job is a stupidly simple process.
  - datavirtue 3y ago
    In my experience wet clutches in automatics far outlasted any dry clutch that I was aware of. Toyotas last a long time but your bog standard iffy Ford AOD clutches would easily last beyond 200k abused. There are many clutch rings packed together and engagement is precise. Fluid changes are fairly easy...or can be. Ford has recently removed the dipsticks on their amazing 6speed truck transmission making it very difficult to change.
dragontamer 3y ago
The diversity in today's transmissions is finally bringing in a golden age... except for manual transmission fans (though still the most economical option, automatics have grossly improved with all of these new technologies). * Hybrids are largely "Power Split Devices" (Toyota / Ford / etc. etc.) which use a planetary gearset to kinda-sorta make a CVT-like approach. * CVTs with belts and/or cones are all available, to varying qualities. * Dry DCTs have created sub-100ms shifts in automatic transmissions * ZF8 (wet-clutch planetary gear / torque-converter traditional automatic) has sub 200ms shifts (~150ms or so for the typical ZF-8). Just old tech but done exceptionally well today.
- whalesalad 3y ago
  CVT's are 100% pure trash. Dig the ZF8 in my RAM a lot. Did not like the 10 speed in my F-150, ZF is much better.
  - zubiaur 3y ago
    Agree on pure IC ones. Hybrid ones, like the one on the Prius, while still technically a CVT, are nothing like the jatco crap Nissan and others had been putting on IC cars. They are quite reliable.
    - kQq9oHeAz6wLLS 3y ago
      The later Nissan CVTs are apparently fine, although they were unable to overcome the damage done to their reputation.
    - brendoelfrendo 3y ago
      The "eCVT" in the Toyota hybrid system isn't a CVT at all, but rather a system that uses the electric motors with planetary gearsets to keep the engine operating as close to its optimal RPM as possible: https://youtu.be/O61WihMRdjM?si=hPoLm8EZnbiLH60h https://youtu.be/O61WihMRdjM?si=hPoLm8EZnbiLH60h
  - hinkley 3y ago
    I think it was Honda who tried out a 2 motor planetary gear setup to eliminate the transmission and I don't know why it was abandoned because it was brilliant. The idea was that you need a certain velocity and torque to hold the drive train at a given speed, and instead of using reconfigurable gearsets for that, you use a differential, and one of the output shafts is sometimes an input shaft. One of the output shafts is attached to the wheels, the other to a motor. At some speeds output shaft B is stationary. To accelerate, you feed power into the motor and now it's speeding up shaft A. At lower speeds, you bleed power off of shaft B by running the motor as a dynamo, using it to charge the batteries and run auxiliary equipment. In the hybrid version there was an ICE on the input shaft (or an ICE and a ganged electric motor) but on a full electric you could run two motors with different torque curves and balance the inputs for each speed.
threemux 3y ago
Pretty sure Ford's "PowerShift" fiasco soured everyone on dry DCTs. I'm not aware of any that are currently used in light duty passenger vehicles
- elzbardico 3y ago
  In my neck of the woods we called them PowerShit.
  - threemux 3y ago
    Hahaha yes a friend of mine that had an affected Fiesta used that term liberally. Not unrelated, he got rid of the thing and never bought another Ford product again.
carbine 3y ago
Too few people these days understand the delicious sensation you get when coming round a bend, dropping the clutch, shifting gears, and feeling the whoosh of power that results from a mechanical interaction between your body and a machine.
- harkinian 3y ago
  I agree with traditional slushbox automatics. You don't get that distinct gear shift feeling, so it's boring. But DCT seems closer to the manual feeling. Cannot confirm since I've never driven one, but it felt that way as a passenger.
- tekla 3y ago
  I say the same thing about Electric Cars. Being able to effortlessly press someone back into their seat on a open empty road while hearing the whine of the electric motors is incredibly fun, so much more so that manual cars.
  - doctor_ 3y ago
    Mashing the throttle takes literally zero skill, hitting a proper heel-toe will always be more satisfying to me as it has taken years for me to perfect and I still mess up here and there. Plus, a tuned Golf R/STI/Evo can throw people in their seats effortlessly too, and rolling antilag will always sound cool.
    - tekla 3y ago
      Who cares? Years of skill rendered irrelevant by pedal to the metal hmmmmmmmmmmmm/
  - deleted 3y ago
    [deleted]
- fragmede 3y ago
  mechanical empathy
- 3y ago
exabrial 3y ago
I remember my first wet clutch Yamaha motorcycle… and the first time I put regular engine oil in it. Made for a fun time of getting nowhere pretty quickly.
IgorPartola 3y ago
For those lamenting the loss of manual transmissions in cars, have you tried motorcycling? Motorcycling: for when you want to beat a Lambo on a $19k motorcycle in a quarter mile race :) But seriously, they are a great second vehicle to have, or even main vehicle depending on where you live. They are simpler than cars and you can work on them using basic hand tools easily enough. They are cheap and good on gas. And they are just really really fun.
- HPsquared 3y ago
  Even motorbikes can have them... Honda VFR1200F can be specced with a dual-clutch auto.
sandworm101 3y ago
FYSA, manuals can come in wet and dry clutch arrangements. Most manual cars/trucks use dry clutches outside the transmission but most modern motorcycles use a "wet" clutch with the entire transmission/clutch bathed in the engine oil. Doing so saves weight/complexity and keeps everything more rigid. This is also why you can smell a burning clutch plate on a car but not on a motorcycle. But if you ever hear a Ducati motorcycle that sounds odd at idle, sounding like it is broken, that sound may be because Ducati is one of the few major brands that used external "dry" clutches.

35 points by luu 3y ago

Wet. Dry have issues due to heat management and failing seals that end up slathering the clutch in lubricants. It boggles my mind that an engineer would choose dry. I think the idea was to reduce costs. In Ford's case it resulted in a fairly nasty class action law suit.

HPsquared 3y ago
Wet clutch has the problem of friction material building up in the fluid, which can cause wear and deteriorate the other components. Dry clutch is more modular, the clutch is more self-contained and seems like it would be better for long-term serviceability: if the clutch wears out, you can just replace that part.
- rozap 3y ago
  Hm thanks for reminding me that I need to change the fluid in my DSG. It's annoying that the VW manual suggests comically long service intervals for this stuff to make it look like the running costs are lower than they are. I want to just keep the car until it has 300k+ miles. But it's all about shifting those units initially.
- kube-system 3y ago
  I've always wondered if it would be able to build a car transmission with a clutch similar to a motorcycle. Those are very easy to replace.
- bri3d 3y ago
  Concentric-shaft wet DCTs aren't bad - for example, replacing the clutch pack on a VW DQ250 is very similar to replacing the torque converter on an automatic. You have to drain it but it's not particularly involved. There's basically a cover on the bell housing behind the flywheel, drain the fluid, remove the snap ring, and you're looking at the clutch pack. Lift it off and lift a new one back on. Rebuilding the clutch packs themselves is a tedious and obnoxious process, because they're a giant stack of friction material that needs to be shimmed into tolerance, but you often just buy the clutch pack as a whole assembly. I'd massively prefer a wet clutch even for long term serviceability - a few hundred dollars or less every year or two for fresh fluid and you've got a long service life before an expensive removal.
- IgorPartola 3y ago
  Wet clutches are standard in motorcycles. Lower power of course but they work very well across the entire segment.
  - fragmede 3y ago
    except for Ducati, famously
    - queuebert 3y ago
      But aren't they meant to be rebuilt every 10k miles or so?
      - IgorPartola 3y ago
        Don’t know about Ducati but on other bikes a clutch job is a stupidly simple process.
- datavirtue 3y ago
  In my experience wet clutches in automatics far outlasted any dry clutch that I was aware of. Toyotas last a long time but your bog standard iffy Ford AOD clutches would easily last beyond 200k abused. There are many clutch rings packed together and engagement is precise. Fluid changes are fairly easy...or can be. Ford has recently removed the dipsticks on their amazing 6speed truck transmission making it very difficult to change.

dragontamer 3y ago

The diversity in today's transmissions is finally bringing in a golden age... except for manual transmission fans (though still the most economical option, automatics have grossly improved with all of these new technologies). * Hybrids are largely "Power Split Devices" (Toyota / Ford / etc. etc.) which use a planetary gearset to kinda-sorta make a CVT-like approach. * CVTs with belts and/or cones are all available, to varying qualities. * Dry DCTs have created sub-100ms shifts in automatic transmissions * ZF8 (wet-clutch planetary gear / torque-converter traditional automatic) has sub 200ms shifts (~150ms or so for the typical ZF-8). Just old tech but done exceptionally well today.

whalesalad 3y ago
CVT's are 100% pure trash. Dig the ZF8 in my RAM a lot. Did not like the 10 speed in my F-150, ZF is much better.
- zubiaur 3y ago
  Agree on pure IC ones. Hybrid ones, like the one on the Prius, while still technically a CVT, are nothing like the jatco crap Nissan and others had been putting on IC cars. They are quite reliable.
  - kQq9oHeAz6wLLS 3y ago
    The later Nissan CVTs are apparently fine, although they were unable to overcome the damage done to their reputation.
  - brendoelfrendo 3y ago
    The "eCVT" in the Toyota hybrid system isn't a CVT at all, but rather a system that uses the electric motors with planetary gearsets to keep the engine operating as close to its optimal RPM as possible: https://youtu.be/O61WihMRdjM?si=hPoLm8EZnbiLH60h https://youtu.be/O61WihMRdjM?si=hPoLm8EZnbiLH60h
- hinkley 3y ago
  I think it was Honda who tried out a 2 motor planetary gear setup to eliminate the transmission and I don't know why it was abandoned because it was brilliant. The idea was that you need a certain velocity and torque to hold the drive train at a given speed, and instead of using reconfigurable gearsets for that, you use a differential, and one of the output shafts is sometimes an input shaft. One of the output shafts is attached to the wheels, the other to a motor. At some speeds output shaft B is stationary. To accelerate, you feed power into the motor and now it's speeding up shaft A. At lower speeds, you bleed power off of shaft B by running the motor as a dynamo, using it to charge the batteries and run auxiliary equipment. In the hybrid version there was an ICE on the input shaft (or an ICE and a ganged electric motor) but on a full electric you could run two motors with different torque curves and balance the inputs for each speed.

threemux 3y ago

Pretty sure Ford's "PowerShift" fiasco soured everyone on dry DCTs. I'm not aware of any that are currently used in light duty passenger vehicles

elzbardico 3y ago
In my neck of the woods we called them PowerShit.
- threemux 3y ago
  Hahaha yes a friend of mine that had an affected Fiesta used that term liberally. Not unrelated, he got rid of the thing and never bought another Ford product again.

carbine 3y ago

Too few people these days understand the delicious sensation you get when coming round a bend, dropping the clutch, shifting gears, and feeling the whoosh of power that results from a mechanical interaction between your body and a machine.

harkinian 3y ago
I agree with traditional slushbox automatics. You don't get that distinct gear shift feeling, so it's boring. But DCT seems closer to the manual feeling. Cannot confirm since I've never driven one, but it felt that way as a passenger.
tekla 3y ago
I say the same thing about Electric Cars. Being able to effortlessly press someone back into their seat on a open empty road while hearing the whine of the electric motors is incredibly fun, so much more so that manual cars.
- doctor_ 3y ago
  Mashing the throttle takes literally zero skill, hitting a proper heel-toe will always be more satisfying to me as it has taken years for me to perfect and I still mess up here and there. Plus, a tuned Golf R/STI/Evo can throw people in their seats effortlessly too, and rolling antilag will always sound cool.
  - tekla 3y ago
    Who cares? Years of skill rendered irrelevant by pedal to the metal hmmmmmmmmmmmm/
- deleted 3y ago
  [deleted]
fragmede 3y ago
mechanical empathy
3y ago

exabrial 3y ago

I remember my first wet clutch Yamaha motorcycle… and the first time I put regular engine oil in it. Made for a fun time of getting nowhere pretty quickly.

IgorPartola 3y ago

For those lamenting the loss of manual transmissions in cars, have you tried motorcycling? Motorcycling: for when you want to beat a Lambo on a $19k motorcycle in a quarter mile race :) But seriously, they are a great second vehicle to have, or even main vehicle depending on where you live. They are simpler than cars and you can work on them using basic hand tools easily enough. They are cheap and good on gas. And they are just really really fun.

HPsquared 3y ago
Even motorbikes can have them... Honda VFR1200F can be specced with a dual-clutch auto.

sandworm101 3y ago

FYSA, manuals can come in wet and dry clutch arrangements. Most manual cars/trucks use dry clutches outside the transmission but most modern motorcycles use a "wet" clutch with the entire transmission/clutch bathed in the engine oil. Doing so saves weight/complexity and keeps everything more rigid. This is also why you can smell a burning clutch plate on a car but not on a motorcycle. But if you ever hear a Ducati motorcycle that sounds odd at idle, sounding like it is broken, that sound may be because Ducati is one of the few major brands that used external "dry" clutches.