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Sudden Drop in Speed When Coming to a Stop

Discussion in 'Engine, Drivetrain, and Exhaust Discussion' started by Nishizawa, Jul 10, 2019 at 11:01 AM.

  1. Nishizawa

    Nishizawa Canada Member

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    Hello fellow forummers! Not sure if I am the only one experiencing this and I am not sure if it has always been there. When gradually braking to come to a complete stop, I notice at around the 20km/h mark, there is a sudden noticeable drop in speed. It is very comparable to engine braking when you shift gear to a lower gear.

    Has anybody else experienced this? Is this normal?
     
  2. Revvdmedia

    Revvdmedia United States Stinger Enthusiast

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    I do think the car engine brakes somewhat when close to a stop. I've noticed it somewhat but never felt it was unusual. I recall there being a gear downshift prior to this happening, so it seems normal.
     
  3. DCBStingerGT

    DCBStingerGT Australia 1000 Posts Club!

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    I also have noticed this , it does feel like engine braking, it would usually happen when I let off on the accelerator pedal, the automatic transmission must go into a lower gear, thus slowing the car faster, even though the brakes are not applied.
     
    • Agree Agree x 1
  4. Secondchance

    Secondchance Canada Member

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    Its definitely the transmission braking, not the engine.

    I believe its the tranny coming out of its coasting and recoupling in 1st or 2nd gear.
     
    • Agree Agree x 1
  5. MerlintheMad

    MerlintheMad United States 5000 Posts Club!

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    Last year this was a complaint by a few. It seems that there is some variability going on here. I and most others notice the trans downshifting as coasting reaches a slower speed. If you do nothing the trans will finally engage 3rd then 2nd gear; and finally 1st as you drop to 1 MPH. There is of course a "bump" each downshift. The difference is in the "violence" of the downshift. Most vehicles are not "violent", but apparently a few are: sort of like a "bam" feeling on each downshift. One or two commenters even said that it is violent enough to make them wonder at first if they had been hit from the rear. :eek: The transmission logic being reflashed (it is a TSB) is supposed to take care of all things transmission-weirdness.
     
  6. Nishizawa

    Nishizawa Canada Member

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    Thank you everybody!

    So I take it that it is “normal”?
     
    • Agree Agree x 1
  7. Revvdmedia

    Revvdmedia United States Stinger Enthusiast

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    Absolutely. I've owned a reasonable number of vehicles and driven numerous others. I have found that each car seems to have unique attributes including things like this. Some cars like the old GMs could just coast for miles off the gas while others seemed to start engine/trans brake immediately when coming off the gas. This car at lower speed definitely is leaning a bit more on the aggressive side of deceleration characteristics, less towards long range coasting.
     
  8. StungnTn

    StungnTn United States Active Member

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    I don't have this issue at all.
     
  9. Kazz

    Kazz United States 1000 Posts Club! STL Stinger Club Texas Stinger Swarm

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    As someone who learned to conserve momentum in previous cars (with manual transmissions), and have had to drive a mother-in-law around in cars for many years (LOL), this is one of the first things I noticed. The transmission has seemingly been designed to be "sporty". So we feel the downshifts at times. Watching how you use the brake as you decelerate you can mitigate this so it doesn't really get noticed.
     
  10. oddball

    oddball United States Active Member

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    By definition it's engine braking. The lag in piston speed is what's slowing the car - nothing in the trans is doing it.

    Every auto transmission is different, and now with computer controlled trans, each car can be different. An auto trans can either freewheel or engage the engine when the driveshaft is turning faster than the engine would be forcing it to turn through the trans. Traditionally, autos were set up to freewheel in the top gear(s) and engage in lower gears for downhill engine braking. But the engagement into the lower gears was usually very slow to make that nice comfortably feeling, and engine tuning generally let engines spin faster easily.

    My experience was the same. Engine braking is a little more aggressive in the stinger, the downshifts are pretty sharp, and the engine is pretty stubborn about slowing down. It won't rev up when turned by the trans. I got used to it in about a month and don't notice now (or my right foot drives around it).
     
  11. Kazz

    Kazz United States 1000 Posts Club! STL Stinger Club Texas Stinger Swarm

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    Sorry, I stand by what I said. What I feel is definitely from the trans.
     
  12. Mr. Tech

    Mr. Tech United States Member

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    I'll experience this occasionally in sport mode. But it's always directly related to a downshift and engine braking. I've never had it happen without a downshift.
     
    • Agree Agree x 1
  13. Secondchance

    Secondchance Canada Member

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    You are somewhat correct, but fail to understand how the gearing in the transmission works, and its effect on and engine when the accelerator pedal is not engaged. The transmission being re coupled into a low gear forces then crankshaft to rotate slower in decel, as there is no opposite force in equal or greater amount causing it to rotate faster causing the gears in the transmission to spin faster.

    "Applying Conservation of Energy: If Torque is constant then angular acceleration can be manipulated by the moment of inertia As inertia is increased, velocity decreases and as inertia is decreased, velocity increases"

    Newtons first law of motion "An object at rest will stay at rest and an object in motion will stay in motion with the same speed and direction unless acted upon by an unbalanced force"

    The lower gear creates the unbalanced force that is pulling against the crankshaft/torque converter/flywheel which in turn slows the engines speed, as its both the force applied, and the stronger force in the scenario. #science!
     
  14. Karl Davlin

    Karl Davlin United States Member STL Stinger Club

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    I found this interesting: I took the Stinger through the Smoky Mountains last week. I noticed that when you use the paddle shifters to drop to a lower gear (engine braking), the car doesn't switch back to 'D' (drive) until you start hitting the gas.
     
  15. Secondchance

    Secondchance Canada Member

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    There are no gears in the engine ( the engine is a single gear ), the change in gear is in the transmission, the force both against and as a result of this, is in the transmission, making it the transmission that brakes.

    the tranny will switch back into d if you cost for too long in low or decel, or at a stop/rolling stop. I find it annoying.
     
  16. MerlintheMad

    MerlintheMad United States 5000 Posts Club!

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    Sport mode will keep the "D" away. :D Until you stop, that is, then a pull on the paddle will bring back the "1".
     
  17. Secondchance

    Secondchance Canada Member

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    oh i know good sir. I do it all the time :)
     
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