Car sometimes still moving when brakes applied

[nnl004]

Tonight the lights ahead changed to amber and I wasn't sure if I'd make it so I hit the brakes. However, to my horror, the car, an automatic BMW 320i, kept moving. I kept hitting the brakes to the floor and it still kept inching forward until it stopped, just outside of the white line I should add so I went through a red. Thankfully , no one was at the junction other than a van next to me. I had my hszards on in the end. What could cause this issue? Both sets of brakes were replaced recently. Apparently an OBD error for the transmission module showing up was recodded but nothing on the dashboard. Time before this happened a couple of weeks ago when I suddenly had to brake at a roundabout, a car in front of me.

[QuickQuack]

Don't take your foot off the brake or reduce the pressure you're applying, keep with firm pressure and let the brakes do their job. "I kept hitting the brakes to the floor..." What you're describing is the ABS system doing its job, but then you interfering with it by taking your foot off/reducing the pressure you're applying, so it doesn't work properly. Common error by the less experienced.

[Leptons]

It could be a master cylinder problem. Is it petrol or diesel?

[nnl004]

Petrol.

[nnl004]

QuickQuack said:

Don't take your foot off the brake or reduce the pressure you're applying, keep with firm pressure and let the brakes do their job. "I kept hitting the brakes to the floor..." What you're describing is the ABS system doing its job, but then you interfering with it by taking your foot off/reducing the pressure you're applying, so it doesn't work properly. Common error by the less experienced.

I've been driving for 4 years, and I have never had this issue. This is my first automatic car though.

[Pica-Pica]

I am trying to interpret what you are saying OP. The car will decelerate all the time your foot is firmly on the brake. Once you have stopped, most automatics will still move (called ‘creep’) if you then take your foot off the brake. Is this what is happening?

[nnl004]

No. I had my foot on the brake all the time but it kept wanting to move forward..It was only after I put the brake down to the max the car stopped.

[Philvrs]

Your first automatic? Genuine question: are you using a foot on each pedal or just your right foot and only pressing either pedal?

[OldGermanHeaps]

Could you feel or hear the abs pump activating?
I had exactly this on a clk with a split reluctor ring on the driveshaft. Normal braking nearly all the time but once in a blue moon pulling up to a junction the abs would kick in when the car was nowhere near skidding and the car just wouln't stop, it would overshoot by a foot or 2.
Abs light worked as normal, and no fault codes recorded.

[InitialDave]

Do you have big feet/wear heavy boots? Could you have been clipping the accelerator pedal at the same time as pushing the brake?

[ChrisNic]

So the car was still moving before it stopped?

[DanL]

nnl004 said:

Both sets of brakes were replaced recently.

Pads, discs, or both? Front and back, or just one end? How recently?

Certainly the one time I’ve had all pads and discs replaced at the same time, brake performance was poor for the first few miles before everything had bedded in…

[911Spanker]

Try it in a safe space with the car in neutral. Then if it still happens, take it to a trustworthy garage for inspection.

Not sure people on here are going to be able to diagnose is correctly from just a description.

[nnl004]

DanL said:

Pads, discs, or both? Front and back, or just one end? How recently?

Certainly the one time I’ve had all pads and discs replaced at the same time, brake performance was poor for the first few miles before everything had bedded in…

Pads, both ends.

The brake pads were replaced weeks ago for the rear and months for the front

[nnl004]

InitialDave said:

Do you have big feet/wear heavy boots? Could you have been clipping the accelerator pedal at the same time as pushing the brake?

Nope, wearing normal shoes which I've worn before

[nnl004]

OldGermanHeaps said:

Could you feel or hear the abs pump activating?
I had exactly this on a clk with a split reluctor ring on the driveshaft. Normal braking nearly all the time but once in a blue moon pulling up to a junction the abs would kick in when the car was nowhere near skidding and the car just wouln't stop, it would overshoot by a foot or 2.
Abs light worked as normal, and no fault codes recorded.

Couldn't hear anything no

[DanL]

nnl004 said:

DanL said:

Pads, discs, or both? Front and back, or just one end? How recently?

Certainly the one time I’ve had all pads and discs replaced at the same time, brake performance was poor for the first few miles before everything had bedded in…

Pads, both ends.

The brake pads were replaced weeks ago for the rear and months for the front

On a quiet road, do a few hard stops and see what happens. It might help bed the pads in.

[snuffy]

I had a sticking and then jammed throttle cable once on the motorway. So the brakes were fighting the engine. That was a bit hairy !

So when you stopped (or rather didn't), was the engine revving?

[GreenV8S]

nnl004 said:

I kept hitting the brakes to the floor

Could you explain exactly what you mean by that? Imagine you were giving instructions to somebody so they could replicate exactly what you did.

For example, were you holding steady pressure on the pedal or pumping it? How much pressure? Was the pedal hitting the floor?

[nnl004]

@snuffy that sounds like whats happening with my car. It's hard to diagnose and give you all the details as my short term memory of things like this isn't great, I really need to get a dashcam. Also hard to diagnose as its intermittent and only happened twice. All in situations where it is very important for me to stop !