Knock sound on acceleration from stop

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focussed

Well-known member
Joined
Oct 7, 2014
Messages
49
I purchased a new FFE two weeks ago. I am noticing that there is a knock sound every time I accelerate from stop. Has anyone else noticed this?

Even when accelerating after regen/break I can hear a less loud knock. But from a full stop the noise is noticeable.
 
focussed said:
I purchased a new FFE two weeks ago. I am noticing that there is a knock sound every time I accelerate from stop. Has anyone else noticed this?

Even when accelerating after regen/break I can hear a less loud knock. But from a full stop the noise is noticeable.
There can be a little bit of "rocking" in the single-speed gearbox at slow speeds (transitioning between stopping/running). Perhaps that is what you are hearing? And, rather than a "knock", I would describe it as a soft "clunk". I can also often feel it through the brake pedal.

That said, though I usually hear the soft "clunk" just about when I come to a stop, I don't really notice (hear or feel) one when accelerating.
 
focussed said:
I purchased a new FFE two weeks ago. I am noticing that there is a knock sound every time I accelerate from stop. Has anyone else noticed this?

Even when accelerating after regen/break I can hear a less loud knock. But from a full stop the noise is noticeable.

No. I don't hear a knock.
Well, I did for a few minutes once... before I realized there was a loose water bottle in my trunk. When I accelerated it thunked against the hatch. Maybe something is rolling somewhere? Or maybe your trickle charger isn't packed snugly?
 
dmen said:
Well, I did for a few minutes once... before I realized there was a loose water bottle in my trunk. When I accelerated it thunked against the hatch. Maybe something is rolling somewhere? Or maybe your trickle charger isn't packed snugly?
One thing with the FFE: The motor is so quiet you start to hear other things. For a long time I also heard a thunk on acceleration and deceleration. Then I took the mini-maglite out of the glovebox; now I don't hear it. Whenever I hear some new rattle I look around the car and invariably find something left in the trunk or one of the door pockets.
 
I also hear the soft "thunk" some of the time when coming to a stop, accelerating from a stop, or when the car's momentum shifts it from accelerating to decelerating (or vice versa). I don't hear it most of the time...but maybe traffic noise masks it or I'm not paying attention. Perhaps some FFEs have more play in the transmission than others?
 
I noticed when coming down the hill from my house in the morning sometimes I get the same - it seems like when transitioning from regen to actual braking there is a little bump then a little push - wondering if it was just a quirk with the car - doesn't happen all of the time.
 
tinilk and epaminondas observations are in line with what I am noticing. The sound is not there always. I have a hunch that after a few miles of driving, I hear the knock. But when car is cold, I haven't noticed it.
I will keep an eye (ear) to it.
 
I get a loud knock if I lose traction starting from a stop. Happens all the time in the rain if I'm not careful, just happened this morning. I hit the accelerator, tire spins a little, loud knock, and off I go. I can hardly wait to get new tires with better traction.
 
I'm thinking this knock I get is the traction control engaging. I am wondering if this is normal, or something I should have checked out at the dealership. Anyone else have experience with the traction control, and does it thunk?
 
ElectricCleetus said:
I'm thinking this knock I get is the traction control engaging. I am wondering if this is normal, or something I should have checked out at the dealership. Anyone else have experience with the traction control, and does it thunk?
No, the traction control is completely electronic, not mechanical, and simply modulates the motor torque.
 
ElectricCleetus said:
I get a loud knock if I lose traction starting from a stop. Happens all the time in the rain if I'm not careful, just happened this morning. I hit the accelerator, tire spins a little, loud knock, and off I go. I can hardly wait to get new tires with better traction.
Is the "knock" just the sound of tire skidding a little? I can be quite sharp and loud inside the car.
 
I believe it's slack in the gears. I experimented last night in the parking garage at our apartment. Since it's an enclosed space sound echoes pretty well making it easy to hear quiet noises. While driving ~10 MPH I repeated alternated between gently accelerating and immediately going from accelerator to brake pedal. There was a faint clunk every time. Anecdotal evidence suggests that the clunk is louder the faster you're moving at the time. Since the transmission would have gears spinning at a multiple of wheel speed it would stand to reason that there would be more rotational force to cause gear slack to make a sound when the motor goes from trying to spin the gears faster to trying to spin them more slowly. There is no clunk (or at least not an easily audible clunk) if I'm accelerating gently and then shift into Neutral to stop sending torque through the transmission.

It appears to be completely normal.
 
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