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I had brake failure in my 2014 Model S, completely unable to stop, and I sailed through a red light before regen slowed me down enough to turn off into a drivew

I had brake failure in my 2014 Model S, completely unable to stop, and I sailed through a red light before regen slowed me down enough to turn off into a driveway. I know you're thinking it was pedal error or something similar and I would definitely dismiss someone else's story the same way. It was not reproducible. But I am 100% certain that the brakes were not responding even using both feet on the brake. My best guess is that something was unexpectedly frozen given the outside temperature at the time. [ I still later traded it in and bought a new Y though, lacking better EV options at the time. /shruggie ]

jacquesm 4y ago
Wow, so the mechanics failed but the electrical part still worked. That's pretty shocking, it should have been the other way around every time. I'm trying to think of how the brake system could have been designed that this would even be possible, the only thing that I can imagine is that a dual piston master cylinder had one of the pistons freeze solid so that the whole system failed to move. But that should be pretty much impossible. One of the disadvantages of regenerative brakes is that if you use them well that you will end up using your hydraulic brakes less than normal which can cause the pistons to seize (and which is an expensive repair if they don't free up by themselves), did the brakes function normally prior to this or did you not use them for a long time?
- s3graham 4y ago
  It hadn't been driven in a couple days, and it was slightly below 0 C. So I guess it's possible something froze, but it wasn't excessively cold out. I am mostly a one-pedal/regen driver, but the brakes had to have been working a few days prior because the car doesn't fully stop without using the hydraulic brakes to go from low speed -> stopped. But after low speed testing in the parking lot I turned into I couldn't reproduce any failure so I barely had anything to report that would have been credible. I also learned that you can't slam on the parking break (what I would have called an emergency brake in other cars!) because it's software-disabled above very low speeds.
  - jacquesm 4y ago
    You may have water in your brake fluid then. Brake fluid is very hygroscopic you should totally exchange it very two years or so regardless of how full the container is. Once unstuck it would stay unstuck until the next freezing cycle. You can have a cheap water contents test done for your brake fluid at almost any garage.
  - ceejayoz 4y ago
    > But after low speed testing in the parking lot I turned into I couldn't reproduce any failure so I barely had anything to report that would have been credible. If it happens again, remember, Teslas collect and send an enormous amount of telemetry. It's very possible just with a time period they'd be able to look into it.
- starwind 4y ago
  > so the mechanics failed but the electrical part still worked. Electric cars use brake-by-wire. Push on brakes, computer processes signal, computer applies brakes. Glitch somewhere in that system
  - jacquesm 4y ago
    Not for braking past a specific point, it's just regular hydraulics once you get out of the range for regenerative braking.
    - starwind 4y ago
      Hmm, interesting. I didn't know that
      - jacquesm 4y ago
        Brembo is working on an all-electric braking system where the calipers are actuated by a servo system but afaik this has not been released yet and even then you'll need to meet or exceed the kind of performance you expect from regular hydraulic brakes to ensure that in an emergency situation that car can be stopped fast enough, which regenerative brakes can not normally provide (if only because the electrical system could fail).
happytoexplain 4y ago
What is "regen"?
- garrettr_ 4y ago
  Regenerative braking
- sp332 4y ago
  When you lift your foot off the accelerator, the car starts to run the motors "in reverse", charging the battery with some of your momentum. So the car slows gradually even if the brake pedal is unresponsive.
mywittyname 4y ago
Did your Model S have a camera pointed at you as a driver? It's going to be so much easier to prove such cases when video evidence of the driver's reaction during the incident is available.
smegsicle 4y ago
> regen slowed me down good thing the battery wasn't full
rhacker 4y ago
I mean it's all in software right? So if a system crashes and there is a relay that tells the motor to spin, not spin (which is probably not how variable speed works) but follow me = then if that subsystem crashed (some exception is thrown) and the code cannot be recovered - then whatever relay state the vehicle was in may just stay that way. ICE vehicles may be much more complicated, and we all know they're going away, but let's not dismiss these real issues.

jacquesm 4y ago

Wow, so the mechanics failed but the electrical part still worked. That's pretty shocking, it should have been the other way around every time. I'm trying to think of how the brake system could have been designed that this would even be possible, the only thing that I can imagine is that a dual piston master cylinder had one of the pistons freeze solid so that the whole system failed to move. But that should be pretty much impossible. One of the disadvantages of regenerative brakes is that if you use them well that you will end up using your hydraulic brakes less than normal which can cause the pistons to seize (and which is an expensive repair if they don't free up by themselves), did the brakes function normally prior to this or did you not use them for a long time?

s3graham 4y ago
It hadn't been driven in a couple days, and it was slightly below 0 C. So I guess it's possible something froze, but it wasn't excessively cold out. I am mostly a one-pedal/regen driver, but the brakes had to have been working a few days prior because the car doesn't fully stop without using the hydraulic brakes to go from low speed -> stopped. But after low speed testing in the parking lot I turned into I couldn't reproduce any failure so I barely had anything to report that would have been credible. I also learned that you can't slam on the parking break (what I would have called an emergency brake in other cars!) because it's software-disabled above very low speeds.
- jacquesm 4y ago
  You may have water in your brake fluid then. Brake fluid is very hygroscopic you should totally exchange it very two years or so regardless of how full the container is. Once unstuck it would stay unstuck until the next freezing cycle. You can have a cheap water contents test done for your brake fluid at almost any garage.
- ceejayoz 4y ago
  > But after low speed testing in the parking lot I turned into I couldn't reproduce any failure so I barely had anything to report that would have been credible. If it happens again, remember, Teslas collect and send an enormous amount of telemetry. It's very possible just with a time period they'd be able to look into it.
starwind 4y ago
> so the mechanics failed but the electrical part still worked. Electric cars use brake-by-wire. Push on brakes, computer processes signal, computer applies brakes. Glitch somewhere in that system
- jacquesm 4y ago
  Not for braking past a specific point, it's just regular hydraulics once you get out of the range for regenerative braking.
  - starwind 4y ago
    Hmm, interesting. I didn't know that
    - jacquesm 4y ago
      Brembo is working on an all-electric braking system where the calipers are actuated by a servo system but afaik this has not been released yet and even then you'll need to meet or exceed the kind of performance you expect from regular hydraulic brakes to ensure that in an emergency situation that car can be stopped fast enough, which regenerative brakes can not normally provide (if only because the electrical system could fail).

happytoexplain 4y ago

What is "regen"?

garrettr_ 4y ago
Regenerative braking
sp332 4y ago
When you lift your foot off the accelerator, the car starts to run the motors "in reverse", charging the battery with some of your momentum. So the car slows gradually even if the brake pedal is unresponsive.

mywittyname 4y ago

Did your Model S have a camera pointed at you as a driver? It's going to be so much easier to prove such cases when video evidence of the driver's reaction during the incident is available.

smegsicle 4y ago

> regen slowed me down good thing the battery wasn't full

rhacker 4y ago

I mean it's all in software right? So if a system crashes and there is a relay that tells the motor to spin, not spin (which is probably not how variable speed works) but follow me = then if that subsystem crashed (some exception is thrown) and the code cannot be recovered - then whatever relay state the vehicle was in may just stay that way. ICE vehicles may be much more complicated, and we all know they're going away, but let's not dismiss these real issues.