Car jerks forward when stopping.

[WhiteHat]

I have an Ecoboost auto w/PP. When applying the brakes, my car will occasionally have a jerking/popping feeling right before the car comes to a complete stop. It's like the car is trying to lunge forward. This feeling is usually accompanied by a soft popping sound. It only happens when stopping slowly and it seems to happen more frequently after spirited driving.

The best way to describe the problem is to think of a bubble that is slowly getting bigger as the brake is pressed and the car slows down, then right as I'm coming to a complete stop that bubble pops. Sometimes the popping sound and feeling is harsh and noticeable to the passenger and other times it is soft and only noticeable to me.

Has anyone else experienced this? Any ideas what it could be?

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[mc lane]

probably it is the Auto trans shifting down to 1st gear. in 1st you have much more torque, so your engine pushes the car more intense than in the higher gears, so the engine pushes it "over" the Brakes.
try this
use Manual mode of the trans. if you are in 3rd or 4th leave the trans untouched and slow your car down to a stand still (the 6R80 trans in your Mustang is the same as in the Ranger Pick up. in the ranger the trans stays at least in 2nd, even if you come to a standstill, so there should not be that jump foreward. so if in Manual mode the effect does not happen, the Thing you observed is the shift to 1st...

 

[paul123]

your car have different modes to tune the transmission Normal | Sport, etc? Same deal in all of them?

 

[WhiteHat]

probably it is the Auto trans shifting down to 1st gear. in 1st you have much more torque, so your engine pushes the car more intense than in the higher gears, so the engine pushes it "over" the Brakes.
try this
use Manual mode of the trans. if you are in 3rd or 4th leave the trans untouched and slow your car down to a stand still (the 6R80 trans in your Mustang is the same as in the Ranger Pick up. in the ranger the trans stays at least in 2nd, even if you come to a standstill, so there should not be that jump foreward. so if in Manual mode the effect does not happen, the Thing you observed is the shift to 1st...

For this test, do I use the paddles to downshift while in manual (S) mode or am I letting the car do that?

your car have different modes to tune the transmission Normal | Sport, etc? Same deal in all of them?

It occurs in Normal and Sport+ toggle modes, but it's more noticeable in Sport+ mode. I haven't noticed it in Track mode, but I don't use that mode often. Haven't used Snow/Wet mode.

 

[jasonstang]

shift to neutral before coming to a stop see if that goes away. It's just the transmission shifting to 1st.

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