Author Topic: Ford PowerShift Transmission Fiascorama Extravaganza  (Read 1219 times)

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Offline soldar

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Re: Ford PowerShift Transmission Fiascorama Extravaganza
« Reply #25 on: July 29, 2019, 09:49:57 pm »
As an American used to torque converters, what is the proper way to drive a dry double clutch automatic transmission?


From everything we're seeing the answer is "don't!". Don't even think of buying one! :)
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Online bdunham7

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Re: Ford PowerShift Transmission Fiascorama Extravaganza
« Reply #26 on: July 29, 2019, 10:13:03 pm »
I've kind of been following this for some time now but never really understood the technical part of the problem.

This reminds me a lot of the Boeing 737 Max problem. The product needed to be rushed to market. Half way through the design the engineers said "this won't do" but management said "we can't turn back and start over now, we don't have that kind of time, so just get it out the door as best you can and we'll find a fix later". By the time Ford realized there was no possible fix they had already sold more than half a million units. While they could they bullshitted customers, they gave them the runaround, etc. The mess has resulted in a class action lawsuit which is under way.

OK, so that part I think I have the big picture covered. What I don't quite understand is the technical part because it is not talked about much.  Double clutch gear boxes are common in other cars and work well so, obviously, mistakes were made in the design. What are the causes that make these boxes bad? What is the design flaw? I mean, a gear is a gear and a clutch is a clutch, it's not like Ford invented all this. What's the problem?

 https://www.youtube.com/watch?v=KBfVqdo576w?t=0

 https://www.freep.com/in-depth/money/cars/ford/2019/07/11/ford-focus-fiesta-transmission-defect/1671198001/

 https://www.youtube.com/watch?v=5WDswUZcit8?t=0

The technical issues really boil down to bad implementation (quality) rather than a single basic design inadequacy--although the dry dual-clutch idea has inherent issues of its own.  This reminds me of the all-electronic non-overrunning Chrysler Ultradrive/A604 that they introduced in 1989 that had failures requiring replacement by the truckload.  I suspect the issues are similar--poor quality control and cheapened parts due to cost control rather than any real issue with a novel design.  The Focus trans has multiple issues that aren't explained simply by the inherent issues with the dry-dual-clutch design.  The have seal leaks and mechanical control problems.  They don't just slip and judder from stops, they quit working altogether.  They suddenly engage and disengage when they shouldn't.  They don't get the right gear.  They fail shifts and you end up coasting for a while.  They leak, and then they leak again.  As with the Ultradrive, the design can work well if it doesn't break.

IMO, the problem is that a proper quality transmission of this design would actually be much more expensive than a conventional automatic because of the mechanical controls required to make it operate--it has to physically select the 6 gears and then modulate the clutch controls.  Transmissions are expensive as it is, so I'm sure they didn't want to spend MORE than they were spending on the old TC-fronted automatics, so they came out with an untested, cheapened version and not surprisingly, it was a POS.  All in all, sadly, a colossal screw up that really doesn't have a fix.  Even sadder, I own Ford stock and a 2014 Focus--but mine  is the Electric, so no trans issues yet.
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Offline Bassman59

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Re: Ford PowerShift Transmission Fiascorama Extravaganza
« Reply #27 on: July 29, 2019, 11:14:10 pm »
Is this another dry clutch versus wet multi-plate clutch thing, like the VW/AUDI gearbox debacle?

Wet multi-plate seems to be much more reliable, AFAIK......(touches wood...)

Yes. Although the reliability is basically the same, just no one can do a clutch replacement on these gearboxes. I've seen DSG boxes needing replacement clutches at 40k miles  :wtf:

I don't know whether the VW DSG transmission uses a wet or dry clutch or what. All I know is that the cost of routine maintenance at 40,000 miles was such that I wanted to part of it.
 

Online amyk

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Re: Ford PowerShift Transmission Fiascorama Extravaganza
« Reply #28 on: July 30, 2019, 12:39:12 am »
ZF makes some of these new type of transmissions for buses and they are horrible to ride in. There is a torque converter but it locks up almost immediately, giving very jerky and slow acceleration complete with throttle dips like a manual transmission would shift. Normal automatics can keep the engine at the RPM for peak torque when they shift, making for faster and smoother acceleration.
That sounds like bad implementation. The smart systems now tie the gearbox control into the engine control system, so they can do rev matching as they change gear.
The "rev matching" is the problem --- the older automatics, like Allisons and Hydramatics, can shift under full power, giving smooth uninterrupted acceleration. The new "computer controlled manual transmissions" can't, making for a much rougher and slower acceleration more like a human driving a manual transmission.
 

Offline John B

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Re: Ford PowerShift Transmission Fiascorama Extravaganza
« Reply #29 on: July 30, 2019, 02:21:51 am »
I remember a comment from an automotive engineer who stated that the shift mapping, and all the associated variables of timing retardation, line pressure control etc, was far more involved than engine mapping. It wouldn't be surprising to find that companies just run out of time and budget to sort out the transmission. Not that it's an excuse, but an explanation. Even a common transmission will require tweaking between different engine pairings.
 

Offline Circlotron

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Re: Ford PowerShift Transmission Fiascorama Extravaganza
« Reply #30 on: July 30, 2019, 02:43:38 am »
Even 20 year old torque converter planetary automatics have these design compromises. Some slightly overlap the engagement of the clutch bands to make the shifts smoother at the cost of wear and heat generation.
That's where the General Motors Turbo 300, 400 and 700R4 series autos were brilliant. No overlap. When the next higher gear comes in it simply overruns the previous gear courtesy of a sprag. There is no lower limit to shift speed that will cause flaring. Just a clutch pack gradually squeezes up and takes over. That's my rough explanation at least. Anyone is welcome to correct me.
 

Online bdunham7

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Re: Ford PowerShift Transmission Fiascorama Extravaganza
« Reply #31 on: July 30, 2019, 08:31:19 pm »
Even 20 year old torque converter planetary automatics have these design compromises. Some slightly overlap the engagement of the clutch bands to make the shifts smoother at the cost of wear and heat generation.
That's where the General Motors Turbo 300, 400 and 700R4 series autos were brilliant. No overlap. When the next higher gear comes in it simply overruns the previous gear courtesy of a sprag. There is no lower limit to shift speed that will cause flaring. Just a clutch pack gradually squeezes up and takes over. That's my rough explanation at least. Anyone is welcome to correct me.

You've got it right--the THM400, etc were fully overrunning, but the downshifts are what actually benefited the most.  Most other transmissions were overrunning for at least the 1-2 shift, one important reason for this is to prevent the coast-up lurch as you come to a stop sign.  With an overrunning gear, you can shift into first at any time and there is no back torque.  With a non-overrunning design, it is difficult to time the coast-down shift-down points so as to both keep it smooth and not get caught between gears when the driver goes again. 

A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit DMM is good enough for most people.
 

Online amyk

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Re: Ford PowerShift Transmission Fiascorama Extravaganza
« Reply #32 on: July 31, 2019, 03:11:25 am »
The 2-3 shift on the 700R4 does involve releasing a band and applying a clutch, so if they overlap it becomes overdrive (4th), and if they both release then the engine flares up.

(I have a 700R4, would've gotten a 4L80 because they're stronger but didn't find a fully mechanical conversion for them at the time. If I didn't need overdrive I would've used a TH400.)
 


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