Double clutching the downshift.

Discussion in 'Hangar Talk' started by Arnold, Oct 15, 2020.

  1. Tom-D

    Tom-D Taxi to Parking

    Joined:
    Feb 23, 2005
    Messages:
    34,736
    Display Name:

    Display name:
    Tom-D
    I learned to drive on a 1954, Brockway 4 under a 4 speed, Yep, I knew how to double clutch.
     
  2. Dan Thomas

    Dan Thomas Final Approach

    Joined:
    Jun 16, 2008
    Messages:
    7,229
    Display Name:

    Display name:
    Dan Thomas
    Drivers of automatics are largely ignorant of its capabilities. What do they think the last three characters of PRNDL321 are for? I am amazed at the cars with their brake lights on for an entire three-mile downhill in the mountains.
     
    PaulS likes this.
  3. kgruber

    kgruber En-Route

    Joined:
    Jan 3, 2007
    Messages:
    4,537
    Location:
    Western Washington
    Display Name:

    Display name:
    Skywag
    Simple..............to add smoothness.
     
  4. kgruber

    kgruber En-Route

    Joined:
    Jan 3, 2007
    Messages:
    4,537
    Location:
    Western Washington
    Display Name:

    Display name:
    Skywag

    Rev-matching is only half the equation. The clutch has to be out while you rev-match for smoothness. Thus.....the double clutching. Max smoothness!
     
  5. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

    Joined:
    Jun 7, 2008
    Messages:
    13,007
    Location:
    DXO124009
    Display Name:

    Display name:
    Light and Sporty Guy
    Wikipedia
    The first car to use a manual transmission with synchromesh was the 1929 Cadillac,[5] however most cars continued to use non-synchronous transmissions until at least the 1950s. In 1947, Porsche patented the split ring synchromesh system, which went on the become the most commonly design for passenger cars.[6] The 1952 Porsche 356 was the first car to use a transmission with synchromesh on all forward gears.[7][8] In the early 1950s, most cars only had synchromesh for the shift from third gear to second gear (drivers' manuals in vehicles suggested that if the driver needed to shift from second to first, it was best to come to a complete stop beforehand).
     
  6. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,258
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    I've never seen a vehicle with PRNDL321 on it, lol. Not much need for the "L" if you can select 1/2. These days it's morphed more into PRNDM.
     
  7. Arnold

    Arnold Cleared for Takeoff

    Joined:
    Mar 8, 2005
    Messages:
    1,191
    Location:
    Philadelphia Area
    Display Name:

    Display name:
    Arnold
    2 is good for starting on snow.
     
  8. PaulS

    PaulS Touchdown! Greaser!

    Joined:
    May 29, 2007
    Messages:
    10,946
    Location:
    New England
    Display Name:

    Display name:
    PaulS
    And smoke coming from the wheels.
     
  9. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,258
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    Yup, easier to crawl with it. I doubt 95% of drivers ever use anything other than P/R/D. Most don't even know what overdrive even means.
     
  10. Arnold

    Arnold Cleared for Takeoff

    Joined:
    Mar 8, 2005
    Messages:
    1,191
    Location:
    Philadelphia Area
    Display Name:

    Display name:
    Arnold
    Hmm. Makes me wonder what EV drivers do. I guess the control logic senses wheel spin and compensates.
     
  11. Salty

    Salty Final Approach

    Joined:
    Dec 21, 2016
    Messages:
    7,693
    Location:
    FL
    Display Name:

    Display name:
    Salty
    apparently, you've been doing it wrong for 35 years. You wouldn’t be the first.
     
  12. genna

    genna Pattern Altitude

    Joined:
    Feb 5, 2015
    Messages:
    1,531
    Display Name:

    Display name:
    ТУ-104
    You're going to have to explain to me how double clutching adds to smoothness in syncho transmission. The entire reason to double-clutch is to match the rotational speeds of input and output shafts inside transmission before putting car in lower gear. This is basically required with dog gears(if you are planning on using clutch at all), but pretty pointless with synchros. You do the first clutch release in neutral. So it adds nothing to smoothness of drive-train since it is effectively disengaged at the moment inside transmission. I have never felt any non-smoothness moving gear lever from 3-2 or any other gear combination prior to releasing the clutch(would be the second release in double-clutching) which is where the "normal" rev matching comes in.

    Maybe I'm missing something.

    This is double-clutching as I understand it(from memory):
    1. Press Clutch(disengage engine from transmission)
    2. Move gear lever to neutral.. This slows input shaft, output shaft is spinning with wheels
    3. Release clutch(first clutching). This spins up input shaft.
    4. Rev to match input shaft rotation to output shaft.
    5. Press Clutch
    6. Move gear lever to new gear
    7. Rev match engine to input shaft
    8. Release clutch

    Only 7 and 8 are responsible for smoothness
     
    tjfelles likes this.
  13. smv

    smv Pattern Altitude

    Joined:
    Dec 30, 2019
    Messages:
    1,663
    Display Name:

    Display name:
    smv
    Unless it is an '06 Dodge Ram. This is the only automatic transmission I have ever driven that will NOT stay in 2nd gear. It will, on its own, downshift to 1st whenever the hell it wants (with 2nd selected) . When using engine compression to ease down an icy hill and the tranny suddenly decides it wants 1st, things can get a little interesting.
     
  14. Arnold

    Arnold Cleared for Takeoff

    Joined:
    Mar 8, 2005
    Messages:
    1,191
    Location:
    Philadelphia Area
    Display Name:

    Display name:
    Arnold
    [Edit - Delete misc. phrase]
    I bet.
     
  15. weilke

    weilke Touchdown! Greaser!

    Joined:
    Jan 26, 2010
    Messages:
    14,368
    Display Name:

    Display name:
    weilke
    Outside of a total brake failure, I don't see a reason to ever shift from 2nd to 1st. Other than that, if I slow down gradually, I will shift down through the gears as required. If I come down a hill under load and use the engine for braking, I will double clutch/blip as the transmission doesn't seem to like having to sync the gears at those higher rpms.
     
  16. Tom-D

    Tom-D Taxi to Parking

    Joined:
    Feb 23, 2005
    Messages:
    34,736
    Display Name:

    Display name:
    Tom-D
    It is smoother when you speed shift, just slide the stick out of gear when they have no pressure, and match the gear when you slide the stick back in they match gears rotational speed. then stand on it. :)

    I'd brake something if I tried it today.
     
  17. PaulS

    PaulS Touchdown! Greaser!

    Joined:
    May 29, 2007
    Messages:
    10,946
    Location:
    New England
    Display Name:

    Display name:
    PaulS
    You need to double clutch a car with synchros from repeatedly screwing up the clutchless shifts over the last 50 k miles, wearing out the synchros....
     
  18. Zeldman

    Zeldman Touchdown! Greaser!

    Joined:
    Jun 13, 2014
    Messages:
    13,572
    Location:
    high desert NM
    Display Name:

    Display name:
    Billy
  19. Dan Thomas

    Dan Thomas Final Approach

    Joined:
    Jun 16, 2008
    Messages:
    7,229
    Display Name:

    Display name:
    Dan Thomas
    You're young. Cars and trucks had PRNDL's for many years. My Sonata has the six-speed auto with the manual shift position, like most now, and I use it to hold the car back on long downhills. Saves the brakes. And the brake light bulbs..........
     
  20. flyingron

    flyingron Touchdown! Greaser! PoA Supporter

    Joined:
    Jul 31, 2007
    Messages:
    20,067
    Location:
    Catawba, NC
    Display Name:

    Display name:
    FlyingRon
    I learned double clutching on a 1980 Seagrave pumper.

    The amusing thing for me is my Chevy Volt has a PRNDL which really is just a digital input to the computer (other than the mechanical PARK lock). Reverse just tells the controller to flip the motor polarity. N applies a very small hold current. D is just R in the opposite direction. L is the same as D if your foot is on the "gas" but applies a more aggressive regenerative braking if you take your foot off.
     
  21. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,258
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    I was speaking specifically to having the "low" option in addition to the 1, 2, 3 options. There would be no need for the L if you could manually select all the gears individually. I may be young-er, but most all of my vehicles were pre-2000 era and had the ubiquitous 4-speed autos in the ones that weren't 5-spd manuals. That said, I've never really had reason to use anything other than overdrive or "3" if I'm towing. Not many hills large enough in OK that necessitate downshifting an auto tranny, lol.
     
  22. Salty

    Salty Final Approach

    Joined:
    Dec 21, 2016
    Messages:
    7,693
    Location:
    FL
    Display Name:

    Display name:
    Salty
    All I know is that “D is that way”

    for those that need help with the reference

     
    Last edited: Oct 15, 2020
  23. weilke

    weilke Touchdown! Greaser!

    Joined:
    Jan 26, 2010
    Messages:
    14,368
    Display Name:

    Display name:
    weilke
    I dont recall ever seeing a 1 on the selector. I remember the 4-speed selector as PRND32L with the 'low' keeping it in 1.
     
  24. Daleandee

    Daleandee Cleared for Takeoff

    Joined:
    Mar 4, 2020
    Messages:
    1,101
    Display Name:

    Display name:
    Dale Andee
    I presently have four vehicles that I rotate through driving duties. Three are manual shift with the "74 VW Beetle being the most fun. The motorcycle is very easy to shift. Yes, I upshift and downshift as needed. Learned the art of the double clutch years ago when driving a 1956 GMC Scenicruiser bus.

    Seems to me that the ability to drive a standard is like flying a tail wheel airplane. Some love to do it and others don't care for it at all. To each their own ...
     
    FormerHangie likes this.
  25. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,258
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    I've seen different options in different vehicles. Sometimes it's PRNDL, or PRN(D)3 1-2, or PRND21. The manufacturers can opt for whatever configuration they want. The 1-2 option I specifically remember from an 89 Jeep XJ.
     
  26. Rgbeard

    Rgbeard Pattern Altitude

    Joined:
    Aug 26, 2017
    Messages:
    1,938
    Location:
    Phoenix, AZ and Ensenada, Mexico
    Display Name:

    Display name:
    rgbeard
    Someone needs to create a Millenial-friendly translation for our younger crowd re: this topic.
     
  27. ElPaso Pilot

    ElPaso Pilot Pattern Altitude

    Joined:
    May 26, 2006
    Messages:
    1,572
    Display Name:

    Display name:
    ElPaso Pilot
  28. A Martin

    A Martin Pre-takeoff checklist

    Joined:
    Jul 28, 2020
    Messages:
    125
    Display Name:

    Display name:
    A Martin
    .

    Downshifting is very beneficial for another reason ...... throttle is closed .... engine vacuum is very high ..... which greatly assists microscopic amounts of engine oil to be drawn up around the piston rings to keep them lubricated and prevent wear.

    I would even consider it the #1 benefit to downshift and braking action #2 benefit . Both are good.

    But there is a #3 benefit as well ... under throttle all bearing surfaces of an engine are under load and during deceleration all the bearings are unloaded in the opposite direction ... this (microscopically) helps the soft main and connecting rod bearings normalize and retain their original shape and size giving them long life.

    #1 Will not work on diesel engines because there is no throttle valve to create a high vacuum but #2 and #3 apply
     
  29. Dan Thomas

    Dan Thomas Final Approach

    Joined:
    Jun 16, 2008
    Messages:
    7,229
    Display Name:

    Display name:
    Dan Thomas
    I grew up in the mountains of BC where highway grades of 7 or 8% weren't uncommon, and we spent plenty of time on logging roads that led to fishing holes, and those roads had some awesome grades. You downshift or die. Brakes get so hot that they fade and soon you have nothing. The biggest off-highway logging trucks had water-cooled brakes, where water was dribbled across the outside of the drum at a rate that would turn most of it to steam and absorb the most heat for the water expended. They had jake brakes, too, but with so much weight on steep hills they needed everything they could get.

    Here's a shot of Highway 20 west of Williams Lake where the highway comes down to the Fraser river:

    upload_2020-10-15_22-28-42.jpeg
     
    Tom-D and MuseChaser like this.
  30. Arnold

    Arnold Cleared for Takeoff

    Joined:
    Mar 8, 2005
    Messages:
    1,191
    Location:
    Philadelphia Area
    Display Name:

    Display name:
    Arnold
    Ah you've missed the joys of 2 or 3 speed automatics with slush box torque converters.
     
  31. Arnold

    Arnold Cleared for Takeoff

    Joined:
    Mar 8, 2005
    Messages:
    1,191
    Location:
    Philadelphia Area
    Display Name:

    Display name:
    Arnold
    Ah, drum brakes. Down a hill and through a puddle - brakes fade away. In my '66 rambler, with one of the above noted transmissions, I rode the brakes through puddles to keep them warm and dry or else stopping became a challenge.

    Truth be told, today's automatics are so good manuals have lost most of their attractiveness. Unless you are one of those folks who would prefer say a Luscombe to a Cirrus. See, there is room in this thread for an aviation comment.:D
     
  32. Bill

    Bill Touchdown! Greaser! PoA Supporter

    Joined:
    Mar 2, 2005
    Messages:
    12,899
    Location:
    Southeast Tennessee
    Display Name:

    Display name:
    This page intentionally left blank
    Grow up somewhere where there are steep windy roads and lots of snow in the winter, and you'll use 2 and 1 a lot. Back in the old school days, most cars were rear wheel drive and did not have ABS. A low gear going down a hill in the snow would allow the rear wheels to hold the car back, freeing up the front wheels to steer. Remember, those cars back then didn't have the brake system finesse and balance of modern cars, and usually had overboosted power brakes. It was quite tricky at times to use brakes downhill and NOT lock up the front tires. No rolling front tires, no steering, hello tree in the corner at the bottom of the steep hill. You learned to use all of the tools in the box.
     
    FormerHangie and Dan Thomas like this.
  33. steingar

    steingar Taxi to Parking

    Joined:
    Feb 6, 2007
    Messages:
    27,937
    Location:
    Land of Savages
    Display Name:

    Display name:
    steingar
    Of course Salty knows nothing of racing turns. You ride a sport bike differently than you ride a scooter. You should probably stick to riding tinker toys. Safer by far.

    Steingar, who has ridden hundreds of thousands of miles over 35 years in four countries and a whole bunch of US States.
     
  34. flyingbrit

    flyingbrit Pre-takeoff checklist

    Joined:
    Apr 21, 2014
    Messages:
    281
    Display Name:

    Display name:
    flyingbrit
    It is on some Fords, like wifey's old Mustang with a C4. Selecting 2 puts it in 2 at all speeds. This reduces torque at the wheels and so aids traction in snow. However on many other vehicles like Chryslers selecting 2 means it can and will go to 1 also and so it is no help with snow.
     
    MuseChaser likes this.
  35. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,258
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    Oh I've certainly used the option when driving rentals in the Allegheny region of PA or along the front range near Denver, CO. I was just saying I don't typically have reason to mess with it in my personal vehicles back in most parts of OK/TX/KS. No point in riding the brakes all the way down a hill to maintain 40mph for a mile if you can just bump it down a gear or two. However, most of the rentals I've done it in just use an "M" position these days and use paddle shifters or the shift stalk to electronically toggle the gears. GM had a particularly odd design in their full size trucks/SUVs where they had an electronic toggle switch on the column-mounted gear selector to move up or down in gear. It's not particular ergonomic to hold your arm straight out and around the steering wheel to try and manipulate the button, especially while descending rapidly down a sweeping turn, lol.
     
  36. Zeldman

    Zeldman Touchdown! Greaser!

    Joined:
    Jun 13, 2014
    Messages:
    13,572
    Location:
    high desert NM
    Display Name:

    Display name:
    Billy
    I remember the 4 wheel drum brake fade well. Nothing like going through water deeper than the bottom of the drums and not having brakes on the other side. All part of the driving experience back then....:lol::lol:
     
  37. kayoh190

    kayoh190 Administrator Management Council Member PoA Supporter

    Joined:
    May 29, 2014
    Messages:
    3,645
    Display Name:

    Display name:
    Kayoh@190
    You forgot to mention your PhD!
     
  38. genna

    genna Pattern Altitude

    Joined:
    Feb 5, 2015
    Messages:
    1,531
    Display Name:

    Display name:
    ТУ-104
    Nonsense! All you need is a starter :cool:;):D
     
    Zeldman likes this.
  39. Zeldman

    Zeldman Touchdown! Greaser!

    Joined:
    Jun 13, 2014
    Messages:
    13,572
    Location:
    high desert NM
    Display Name:

    Display name:
    Billy
    Yeah, I have had to do that a few times as well...:lol:
     
    Daleandee likes this.
  40. steingar

    steingar Taxi to Parking

    Joined:
    Feb 6, 2007
    Messages:
    27,937
    Location:
    Land of Savages
    Display Name:

    Display name:
    steingar
    My first bike had a kickstarter. I'll never know how those guys kickstarted the early Harleys and Indians. I could barely do it for a 400cc parallel twin.