Double-clutch Rev-Matching

[qwkcoupe]

We don't need no stinking DCT, we need a double clutching driver. :headbonk:

We don't have Double Clutch Transmission (DCT) nor electronic rev-match to help out.

Double Clutching Driver (DCD) @ 16 seconds

The purpose of DCD is the same as DCT, smooth power transfer to keep the tires settled while downshifting and save the synchros too. I guess in theory it wears out the clutch pedal pivot point and the throw out bearing 2x as fast.

@ 16 seconds check out the clutch being pressed two times for each down shift, and the same can be done for the upshift too. At the example 16 seconds, that is 6 clutch actuations to down shift 3 gears.

[ame]


I also started shifting without the clutch during normal commuting driving... the shifter falls into gear when the RPM matches with virtually zero hand pressure on the shifter.

So what do you think?

p.s. Mods, I understand if this post has to go to a different forum since it isn't technically about s550 tech.

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[Norm Peterson]

What do I think?

Both techniques are useful to have in one's box of driving skills, and I double-clutch the majority of downshifts that don't involve coming to a complete stop. But I don't and won't recommend normal shifts (either up or down) be accomplished clutchlessly - you won't always get it right/perfect and that'll beat the involved synchros up a good bit worse than will a similar error in rev matching when the clutch is used.

The 'line' between a true double clutch downshift and a simple rev-matched downshift is less distinct than you think. Think about this one a bit.


DSGs with electronic rev-matching seem to be at their best on the race track or during enthusiastic driving. Not always as nice at low speeds and light throttle, and I haven't heard anything either way concerning what the electronic control deal is when you intentionally skip one or more gears on the way down.


Norm

 

[Stuntman]

Not quite...

DCT will always be faster than a standard clutched transmission or even a dogring race box due to the DCTs gear stack being split with the odd gears on one stack with the even gears on another and the interrupted power delivery as the next gear is engaging simultaneously as the other is disengaging. This is a huge advantage and even more so on a turbo car.

AF far as double clutching goes, it is a neat skill to have and won't really waste much times on downshifts and can be slightly beneficial to synchro longevity especially if you skip gears (ie: 5th-2nd). But the gain in longevity probably isn't significant then again it could increase the life for a dying gear that's notchy.

Double clutching on upshifts serve no purpose, is slower and a waste of time. By virtue of the upshift itself, RPMs will be lower once the next gear is engaged so the clutch and input shafts will already be at a higher rpm than the next gear.


0.02

 

[Norm Peterson]

Double clutching on upshifts serve no purpose, is slower and a waste of time. By virtue of the upshift itself, RPMs will be lower once the next gear is engaged so the clutch and input shafts will already be at a higher rpm than the next gear.


0.02

Most of the time, that's true.

But there is at least one exception. That one involves cold temperatures, rapid deceleration of the rotating bits inside the transmission, probably the gear lube not being as readily squeezed out from between the synchro cone surfaces to let friction do its job of matching internal revs, and the avoidance of using too many rpms on a cold engine. Under such conditions it is entirely possible to miss the "sweet spot" for synchromesh engagement on upshift and find the synchro mechanism blocking your engagement of the next higher gear.

Experience finds this to be mainly a 1-2 upshift problem the first couple of times in the morning or after all day at work when the car and everything in it has reached fully cold status, 1-2 being particularly vulnerable due to the large jump in ratio between those gears in most current transmissions.


Norm

 

[qwkcoupe]

Guys, I've enjoyed this enlighten folks about the connected to car joy of driving a manual transmission for all it is worth.

And right on, I did cringe the half dozen times the synchros banged when I missed that clutch less shift during normal slow driving.

:ford:

 

[Stuntman]

Most of the time, that's true.

But there is at least one exception. That one involves cold temperatures, rapid deceleration of the rotating bits inside the transmission, probably the gear lube not being as readily squeezed out from between the synchro cone surfaces to let friction do its job of matching internal revs, and the avoidance of using too many rpms on a cold engine. Under such conditions it is entirely possible to miss the "sweet spot" for synchromesh engagement on upshift and find the synchro mechanism blocking your engagement of the next higher gear.

Experience finds this to be mainly a 1-2 upshift problem the first couple of times in the morning or after all day at work when the car and everything in it has reached fully cold status, 1-2 being particularly vulnerable due to the large jump in ratio between those gears in most current transmissions.


Norm

What car? Synchros dying?

 

[Norm Peterson]

1987 Maxima, 1995 626/V6, 2001 Maxima, '08 Mustang, and '10 Subaru Legacy 2.5GT . . . . All bought new.

Also the TR3550 I installed into a 1979 Malibu (I will note that this car's original Saginaw with a 2.85 1st and 2.02 2nd and the 2.88 1st gear T10 that replaced the Saginaw rarely gave this kind of difficulty). I don't remember much about the 1972 Pinto concerning this matter, either when it was all-OE or after it got a V6 and tranny swap, but we were living in a slightly warmer part of the country at the time.

There is no correlation to vehicle/transmission age (<1 year to 18+) or to mileage (anywhere from under 5000 to beyond 110,000). It's not the synchros, as this never happens during warmer weather and only rarely after the car (transmission) has warmed up a bit in the winter.

Those cars are not and were not drag raced or powershifted, and the OE clutches have tended to last 100,000 miles or more. I learned to drive driving stick about 50 years ago and haven't owned an automatic transmission car for over 40, and this is one of the little things I've unexpectedly learned about manual transmissions along the way (nobody ever told me to expect this).


Norm

 

[Stuntman]

Sounds like the fluid may be too thick. Double-clutch upshifting is still unnecessary since the RPM drops from a lower gear to a higher one on an upshift. Even if you miss the window of opportunity where the RPM matches on the in&output shafts, Synchros are designed to synchronize the speeds of the input and output shafts so the car goes in gear. If you have cold fluid and shot synchros and miss the window of opportunity on an upshift, then in that case it could help.

 

[Norm Peterson]

Like I said, even with less than 5000 miles on these transmissions this happens, and only when cold. No, I don't know how much less than 5000, but we've bought most of our cars during the first 1/3 of the year and none any later than mid-summer. We haven't had fewer than 3 cars since 2001, and live no more than about 5 miles from our principal places of employment, which should help explain the slow rate of accumulated miles.

It's hard for me to believe in this day and age that the OE fluid fills would be any thicker than absolutely necessary just for the CAFE purpose (this is specifically why my '08 gets its 5W20 engine oil spec rather than 5W30, for example). The TR3550 fill (GM Synchromesh fluid) I'll take responsibility for - though it was specifically recommended by the mfr.


Norm

 

[Norm Peterson]

I can't do much more than provide my observations. About the only thing I can add (reiterate?, rephrase?) is that since I'm not particularly interested in drag racing I probably take a little longer making my shifts than those who are into that activity.

Like you say, it'd be nice if the synchromesh mechanisms would do their job under every conceivable situation instead of just most of them. But since they apparently aren't 100.00% of the way to that point and since I doubt I'm the only person who has ever run into this situation it's still worth mentioning what you probably consider a "work-around". No telling who it might help, or when. Call it another skill in your toolkit, to be used as necessary.


Norm

 

[minicobra]

What are the chances the new GT350 will get the Tremec 7spd with rev-matching like in the C7 Vette. ? ?

 

[Norm Peterson]

Is Tremec even making a 7-speed transmission separate from and in addition to the Corvette's 7-speed transaxle? If so, I wonder what the ratios would be, as they might be different (which would affect the choice of ring & pinion ratio and/or tire size).



About Active Rev Matching - that truly sounds like a needless video-game-ish complexity that intentionally takes away part of the fun of driving a car with a manual transmission. I realize it can be turned off in the Corvette application, but why even have it in the first place?

On edit, the people who would most benefit from this feature are very likely the people who downshift as rarely as possible.


Norm

 

[Trackaholic]

Is Tremec even making a 7-speed transmission separate from and in addition to the Corvette's 7-speed transaxle? If so, I wonder what the ratios would be, as they might be different (which would affect the choice of ring & pinion ratio and/or tire size).



About Active Rev Matching - that truly sounds like a needless video-game-ish complexity that intentionally takes away part of the fun of driving a car with a manual transmission. I realize it can be turned off in the Corvette application, but why even have it in the first place?

On edit, the people who would most benefit from this feature are very likely the people who downshift as rarely as possible.


Norm

I have the same type of need for a double-clutch upshift in my 350z (maybe it's a Nissan thing). Even when new, the car would have a difficult time getting into second gear when cold. I've tried many differenct fluids, but never found one that solves the problem. Instead, I just take it easy for the first few minutes of the drive, and do a double-clutch 1-2 shift. Works well enough. The transmission in my Z has never had the best syncros anyway. Maybe an alignment issue, maybe a design issue, but at this point, no big deal either way.

Regarding the rev-matching, I think it is a great option. The times I think I'd want to use it is at the track, where it would help me brake more smoothly and shift more smoothly than my heel-toe capabilities allow. Also reduces the mental load and allows greater focus on the line, other cars, etc. It might turn out that I would hate the feature (and the one time I tested a 370Z on the street, I didn't enjoy it at all), but that's the situation where I think it could come in handy.

-T

 

[minicobra]

About Active Rev Matching - that truly sounds like a needless video-game-ish complexity that intentionally takes away part of the fun of driving a car with a manual transmission. I realize it can be turned off in the Corvette application, but why even have it in the first place?

Norm

I would have been right there with you, had I not spent a fair amount of time on the track with my 370Z. I was reluctant to even turn the feature on because I did not want to think I wasted years of practicing the perfect heel and toe downshift for nothing. Well, after getting over my ego, and trying my best to embrace this new technology, innovation be damned, I actually figured out that this feature would allow me to improve my lap times, because it never makes a mistake and cost me precious seconds. Overall I really enjoyed it in the end, and now that I have the GT500, I actually kind of miss it.

I'm all for innovation and technological advancements, as long as they don't impede on the pure satisfaction of the overall driving experience.
As long as they have an override button, then it's a win -win for everyone.
Want to practice old school heel and toe, just turn it off.

Cars have to evolve, it's just part of moving forward. Otherwise we would still be driving without power steering, anti-lock brakes, traction control, stability control, etc, etc. Reminds me of my old 1970 Boss 302, now that was a driving car, ha, ha.

This might sound crazy, but I've been wishing for years that someone would design an auto/manual trans that can be shifted (with a clutch and stick) and have a full auto mode that can be switched on.

Most of my cars are daily drivers that I take to the track as well, I've been stuck so many times in stop and go traffic for hours on the 5fwy of 405fwy on my commute, cursing my sore foot and leg and clutch almost contemplating purchasing DCT paddle shift car, but then I remind myself of the pure driving experience that the manual has, and talk myself out of it.
I had the opportunity to buy a slightly used 2010 GTR for a great price, but opted out, because it wasn't a manual.

 

[Norm Peterson]

Curiosity at this point, but was the automated rev matching smart enough to know if you were skipping gears or did it simply assume you always downshifted sequentially?

Cars have to evolve, it's just part of moving forward. Otherwise we would still be driving without power steering, anti-lock brakes, traction control, stability control, etc, etc.
Reminds me of my old 1970 Boss 302, now that was a driving car, ha, ha.

Of the four cars we have, only one has ESC, one more has TC only, and the '95 Mazda doesn't even have ABS. It truly doesn't even cross my mind when driving any of
the "under-nannied" cars that I'm missing anything.

Your '70 Boss was actually a pretty refined ride. A friend of mine from autocross who I hadn't seen in years until we both happened to be at NJMP on the same day last month still has this pure driver's car ↓↓↓ . He complains about all those Porsches holding him up going through the technical parts, sometimes beeps at them.



Norm

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