Push forward when I put "D" on the Selector

[cole tricle]

Dear all,

I've a 2018 GT Cabrio with 78.000km and several weeks ago I've noticed a change on the Gearbox.
Basically when I put D I have a push forward on a gearbox, and It did not happen previously, in fact, when I put R the car work fine, does not notice and perceptible move.

I guess is not a normal behaviour, and as I mentioned it did not happen previously; and to give more information the push happens strong or light depending on how the temperature the car is.

Is like the gearbox not retain properly when I change on D.

Any recommendations?

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[sk47]

Hello; I must figure you re talking about putting the transmission in gear (forward drive gear) when you put it in the D setting. My experience on automatics is they do tend to move the car when in gear at idle. Even more so while the engine is cold and tends to run at higher RPM's. Such is normal function of the torque converter.
Two things can be in play. One is already mentioned is the RPM's of the engine when cold. Another can be if the AC is turned on or off. Some, if not most, vehicles run the engine at a higher RPM if you start it with the AC on.
Another thing might be if you have the parking brake engaged or not when you put it in gear.

That you say there is a difference between forward and reverse I do not quite understand. A wild guess being perhaps you park on a slight grade. I will follow the thread in hopes of learning more.

I have to hold my foot on the brake of my automatic vehicle at red lights and other stops to prevent the vehicle from moving forward or reverse at warm idle engine speeds. The is an exception at the federal tunnel between Middlesboro KY and Harrogate TN. traffic is frequently stopped when a hazardous load is in the tunnel. Coming from Middlesboro the grade is uphill and the vehicle at idle will not creep forward at idle speed. Will move backward at idle speed in D so i hold the brake. Going from Harrogate to Middlesboro the grade is downhill so the vehicle will quickly move forward in D so I must hold the brake on.

 

[Tripp051420]

I know exactly what the problem is, you got an automatic! Never would have happened with the proper transmission, a manual!

 

[IPOGT]

Is a Cabrio some special edition in Europe?

 

[MD18EcoStang]

Is a Cabrio some special edition in Europe?

British, cabrio (or cabriolet) = American, convertible

 

[sk47]

Hello; To sum up. Based on what is posted and assuming the car is stock, seems normal for an automatic to move forward when in D at idle on level ground.

 

[cole tricle]

Hello,

From what I can see, I didn't explain myself very well, hehe.

Obviously, the car moves forward when shifting into D, but that's not the point.
The point here is that when I shift from N to D (by pressing the brake pedal) before releasing it, the moment I select D (still pressing the brake, not releasing it), it's as if the car is trying to move forward (rude movement); it's like something isn't holding in the gearbox. Isntead, If I change to N to R, the car is very soft, you don't feel any movement.

Yes, the car is completely stock.

 

[sk47]

when I shift from N to D (by pressing the brake pedal) before releasing it, the moment I select D (still pressing the brake, not releasing it), it's as if the car is trying to move forward

Hello; Such is normal as described. My truck with an automatic does this. Other automatic vehicles I have driven also did such. This is the way a torque converter works.
Once the engine starts the crankshaft spins the front half of the torque converter. The back half of the torque converter is attached to the transmission and if the brakes are applied that half cannot move. The two halves of the converter never touch but need some way to convert the spin of the engine over to the transmission gears.
In a manual trans there is a friction Disk sandwiched between a flywheel attached to the crank and a pressure plate attached to the transmission. We use the clutch pedal to control how much the e friction disk transferes the spinof the engine to the transmission.
In an automatic the fluid in the torque converter (transmission fluid) can apply the spin of the engine to the transmission. It is a fluid coupling and not a physical friction coupling. Picture two box fans one in front of another. Turn one on so it blows onto the second. The wind from the first will spin the blades of the second. Same thing in a cars torque converter.
With the transmission in P or N you start the engine. The secondary half of the torque converter is being spun by the fluid pushed away from the first half. So, both are spinning. In park the spin is pumping pressurized trans fluid thru the body of the transmission, but that fluid is bypassing the gears that move the car.

Push the drive button and a valve of some sort sends that pressurized fluid to engage the gears that drive the car. This is the lurch you describe in D with the brake on. Some things can make the lurch stronger or weaker. RPM is one thing. having the AC on can be another. Modern vehicles can have computer controls which do adjust the fluid pressure. I imagine there are faults in the transmissions which can make this out of spec. However, what you describe seems normal enough unless it is become particularly violent.

You will have to use your judgment as to the violence of the lurch. We following the thread cannot feel it. You perhaps should go to a transmission shop if it is worrisome.
Good luck

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