Strong Jerk During Hard Braking

[Vlad Soare]

Hi,

 

My 2017 hybrid Mondeo started doing something very strange recently. When I brake very hard, it first starts decelerating, then suddenly there's a powerful jerk, then it continues decelerating normally. During normal driving, when I drive smoothly and brake gently until the car comes to a stop, it never happens. It's only hard braking that causes this jerk. And it's really strong, it feels like hitting a sleeping policeman at 40 mph.

There's no other symptom. The car works perfectly every time, under all circumstances, except when braking hard.

Any ideas what the problem might be? I guess I'll have to go to a Ford dealership anyway, but I'm curious as to what could be wrong. I'd like to be prepared when I get there. ?

 

Thank you.

 

Edited August 30, 2020 by Vlad Soare

[ElectricFan69]

How does this compare with ABS pumping action?  Wonky ABS could make jerking motion - but those have typically a robust self-test that set a fault code.

 

I'd look for something loose in either brakes or suspension that moves when applying the friction brakes hard.  It would need to be something with 'sticktion' that would not allow quick movement to the 'reset' position.  Step 1 would be a carefool look at the components for signs of wear or loose components.

[Vlad Soare]

It doesn't resemble the ABS action all. On slippery ground, if I brake hard enough to trigger the ABS, it's extremely smooth. I can barely feel some vibrations in the pedal. Whereas this jerk is strong, the whole car shudders. And it's just one time, just one single jerk, after which the car continues to brake as if nothing had happened.

When this happens I don't feel anything unusual in the brake pedal. It doesn't feel like the pedal were pushed back. And there's plenty of grip, there's no reason for the ABS to activate at all.

Edited September 23, 2020 by Vlad Soare

[eisbaer]

maybe it is this?

 

[MacDonald]

Hard Braking Causes 2018 Hybrid to Jump 

If I brake hard (especially when going even slightly downhill) the car often lurches or bucks once. It seems like the rear brakes seize up for a second. Could this be due to a glitch in whatever controls the balance between electric and mechanical braking.

[OSGOD]

My 2016 Ford Fusion Energi is having the exact same issue. Did you ever figure out what the problem was?

[Vlad Soare]

Sadly, no. I didn't pursue it any further, because I sold the car soon thereafter.

 

[OSGOD]

For anyone trying to fix this issue, the problem ended up being to front suspension control arm.

[Vlad Soare]

Frankly, I don't think it's the control arm. At least in my case I don't think it was. It felt nothing like a suspension issue. Besides, my suspension was fine. The car had only 20K miles on the clock and had undergone a yearly check-up, suspension included, where they had found nothing wrong. But mostly it's the way it felt that makes me rule out the suspension. I know how suspension issues feel. This didn't feel like that. This felt as if the car suddenly stopped braking at all for a split second and then started braking hard again. A faulty control arm doesn't have this kind of effect.

Considering that this behaviour doesn't seem to affect the regular Fusion or Mondeo, but just the hybrid, I suspect it has something to do with the regenerative braking system and the way it's integrated with the normal brake. There might be something about braking hard on a dry surface that's confusing it and causing it to engage or disengage very abruptly. But we may never know for sure.