# Brakes fail - how do you stop?



## ahagge (May 6, 2017)

_Hypothetical scenario:_ You're coming down a mountain road in your Model 3 and when you press the brakes, they go to the floor (hole in the brake line or something similar). _How do you stop?_

As most folks know, ICE cars have at least 3 options at their disposal:

Use the emergency brake
Shift into a lower gear
Turn off the ignition and use compression to slow to a stop
But the Model 3 has none of those options available. From what I can see, the only way to engage the parking brake is to shift into Park, and you can't do that if the vehicle is moving (I _think_).

I realize it's an unlikely scenario these days, but I'd really like to know how to react BEFORE it happens.


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## jsmay311 (Oct 2, 2017)

Does this answer it?






I'd assume the behavior in the Model 3 would be similar. Idk for sure tho. And idk if it's actually called the "parking brake button".


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## DR61 (Apr 10, 2016)

All modern vehicles have dual circuit brake systems. If there is a leak in one, the other still operates. So a major brake fluid leak will leave either full front or full rear brakes functioning.

Also, I think I read that pressing and holding in the parking brake button will activate the emergency (parking) brake, regardless of speed. Can anyone confirm for Model 3?


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## Bokonon (Apr 13, 2017)

jsmay311 said:


> Does this answer it?
> 
> 
> 
> ...


Makes sense.... Come to think of it, the first-generation Volt did something similar if you shifted it into reverse at speed.


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## jsmay311 (Oct 2, 2017)

Bokonon said:


> Come to think of it, the first-generation Volt did something similar if you shifted it into reverse at speed.


Well, that just engages regen, I believe. The Volt has a parking brake button separate from its "gear" shifter.


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## Guest (Apr 10, 2018)

It applies to all modern vehicles, including Model 3:
Use parking brake. In case of manual lever (operated with hand or foot), operate slowly.
In case of electronic button, force is adjusted automatically.

Of course, in case of EV, maximizing regen is step 1. 
In case of extreme electronic brake failure (12V system failure) it is likely that electronic parking
brake will not work. In this case, push brake pedal hard to the floor and do not let go for few seconds.
If vehicle is slowing down, keep holding, if not, let go and push again. If brake booster dies (no power)
brakes will operate with foot force. Which requires extreme pressure to the pedal. No less than "standing on one foot" pressure.
There are exceptions (Nissan Leaf).
Hydraulic lines are redundant in criss-cross logic.


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## garsh (Apr 4, 2016)

ahagge said:


> _Hypothetical scenario:_ You're coming down a mountain road in your Model 3 and when you press the brakes, they go to the floor (hole in the brake line or something similar). _How do you stop?_



All brake fluid master cylinders have been required to be dual-reservoir since 1976 in the US (I'm sure other countries required this around the same time). If you break a brake line, you'll notice a problem because you'll have to mash the brake pedal to the floor. It won't be great, but you'll still have two of your wheels providing some braking.
Regen. You're in an electric car. Turn on heavy regen.
Yeah, there's probably a way to activate the parking brake in an emergency. But I couldn't find anything in the manual. If someone doesn't mind being a guinea pig, try holding down the "park" button while driving at speed to see what happens. That would seem to be the obvious way to activate it to me.
If things are truly desperate, go off the road into a field to add a lot of "friction" and help prevent your car from running into another.


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## ahagge (May 6, 2017)

jsmay311 said:


> Does this answer it?
> 
> 
> 
> ...


Perfect! As long as it works the same way in the Model 3 (AND someone can confirm that the parking brakes are activated with a mechanical linkage instead of the same hydraulic system used for the main brakes), we're golden!


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## MelindaV (Apr 2, 2016)

garsh said:


> Yeah, there's probably a way to activate the parking brake in an emergency. But I couldn't find anything in the manual. If someone doesn't mind being a guinea pig, try holding down the "park" button while driving at speed to see what happens. That would seem to be the obvious way to activate it to me.
> If things are truly desperate, go off the road into a field to add a lot of "friction" and help prevent your car from running into another.


There is a "now you know" video (I think in their 12 days of Model 3 series) where they did just this. It brakes until it hits a low speed, then puts it in Park.


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## teslarob (Oct 31, 2017)

ahagge said:


> Perfect! As long as it works the same way in the Model 3 (AND someone can confirm that the parking brakes are activated with a mechanical linkage instead of the same hydraulic system used for the main brakes), we're golden!


Yes, the parking brake is an electric motor on the back of the rear caliper.


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## CoastalCruiser (Sep 29, 2017)

garsh said:


> All brake fluid master cylinders have been required to be dual-reservoir since 1976 in the US (I'm sure other countries required this around the same time). If you break a brake line, you'll notice a problem because you'll have to mash the brake pedal to the floor. It won't be great, but you'll still have two of your wheels providing some braking.


Just a note here. I had the brakes go out on my 1996 Toyota Corolla Wagon a couple of months ago. The brake lines under the car feeding the rear brakes (not the front) sprung a leak (car used to be on the east coast). It drained the reservoir. When the fluid had emptied the brakes failed... on a hill... pedal went right to the floor.

I did not notice that the car has dual reservoirs. There is certainly only one fill hole. And I have seen dual reservoirs. If this car has one it is not apparent.

None the less my note here is that anything is possible. *Know how to stop you car if the brakes fail*. Test it.

I was lucky in my case, as the car has a readily accessible hand brake on the console. Pulling the handle stopped the car, even on a hill (that's why with conventional brakes (not Model 3) it is wise to check the adjustment in the emergency brake periodically). But I had just bought the car from my neighbor (literally days before). She has a baby, and was clueless about the hand brake when I told her the story. We both felt our guardian angels must have been on the job. The hill only stops when you reach the Pacific Ocean.


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## garsh (Apr 4, 2016)

CoastalCruiser said:


> Just a note here. I had the brakes go out on my 1996 Toyota Corolla Wagon a couple of months ago. The brake lines under the car feeding the rear brakes (not the front) sprung a leak (car used to be on the east coast). It drained the reservoir. When the fluid had emptied the brakes failed... on a hill... pedal went right to the floor.


When that happens, pump the brakes. There should still be pressure to two of the wheels, but it may require a couple of full-force, to-the-floor pumps of the pedal to get them to work.


> I did not notice that the car has dual reservoirs. There is certainly only one fill hole.


Like I said, all cars since 1976 have them. Some have two completely separate reservoirs, but most OEM ones have a single tank with a partial internal divider, and only a single fill hole.


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## CoastalCruiser (Sep 29, 2017)

Yeah, mine is similar to the one pictured. Clearly, pumping the brakes should be part of a well thought out get-out-of-rolling-down-the-hill strategy. ;>


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## PNWmisty (Aug 19, 2017)

I guess it's good to know how to bring the car to a stop if both regular brake circuits failed simultaneously but that would be extremely rare on a car that was maintained in any reasonable manner. It would require neglecting to fix the problem of one brake circuit failing or the even more rare case of both circuits failing simultaneously.
More of a theoretical concern than a practical one.


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## DWhatley (Jun 16, 2018)

MelindaV said:


> There is a "now you know" video (I think in their 12 days of Model 3 series) where they did just this. It brakes until it hits a low speed, then puts it in Park.


I enjoyed going back to the Now You Know 12 days of Model 3 playlist but the braking demo was not among the things they showed.


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## NO BRAKS (Oct 17, 2018)

DR61 said:


> All modern vehicles have dual circuit brake systems. If there is a leak in one, the other still operates. So a major brake fluid leak will leave either full front or full rear brakes functioning.


Correct, except that in passenger cars each circuit is diagonally linked, i.e. if one circuit fails you'll be left with front left plus rear right or vice versa. This prevents the oversteer associated with rear-only braking.


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## Karl Sun (Sep 19, 2018)

garsh said:


> If someone doesn't mind being a guinea pig, try holding down the "park" button while driving at speed to see what happens. That would seem to be the obvious way to activate it to me.


 Didn't have my g-meter installed for these tests so I'm using (guessing with) my semi-calibrated butt-o-g-ometer.

40 MPH level road, engage (hold) parking button for one second. Vehicle immediately slows at about 0.4g as long as the button is pressed, stops decel (back to normal regen braking level) immediately when button is released.

Holding the Park button longer (perhaps more accurate when speed gets below ~20 MPH) braking decel rate increases significantly, perhaps to 0.8g. I did not come to a complete stop.

Methinks the Park button engages the elec motors on the rear calipers to which initially are not strong enough to engage heavy braking or lock the rear wheels (small pad area, single piston, 4300 Lb vehicle, ...). Then, as the pads/rotors heat up and as speed decreases, friction in the rear [brakes] increases enough where it will stop the car more quickly .

I ddi not take IR temp readings of front and rear rotors to see if any front friction action was occurring. My laziness again.

This method can't be [easily] modulated to make a smooth stop.


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## Dr. J (Sep 1, 2017)

Karl Sun said:


> This method can't be [easily] modulated to make a smooth stop.


So.....not a useful alternative to the (functioning) brake pedal.


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## Karl Sun (Sep 19, 2018)

Dr. J said:


> So.....not a useful alternative to the (functioning) brake pedal.


 Accurate statement. Unless you are trying to get that loose filling out?

More data: Pushng the Park button at speeds lower than 20 MPH just makes the car beep at me. It does NOT activate the same braking function that happens at 40 MPH. I have not [yet] tested where between 40 and 20 MPH this change occurs nor have I tried allowing the car to come to a complete stop using the Park button from 40 MPH.

So many things to test, so little miles driven!


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## Bullwinkle J Moose (Sep 6, 2018)

>You're coming down a mountain road in your Model 3 and when you press the brakes, they go to the floor
As mentioned above - the *first* thing to do in this scenario is to *pump* the brakes. Often there's enough fluid still in the system you can build up pressure by pumping.

That's always your first line of defense. Before trying any of the other more radical techniques.


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## Dr. J (Sep 1, 2017)

Bullwinkle J Moose said:


> >You're coming down a mountain road in your Model 3 and when you press the brakes, they go to the floor
> As mentioned above - the *first* thing to do in this scenario is to *pump* the brakes. Often there's enough fluid still in the system you can build up pressure by pumping.
> 
> That's always your first line of defense. Before trying any of the other more radical techniques.


I'm surprised no one has mentioned the Fred Flintstone technique.


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## Karl Sun (Sep 19, 2018)

Update:
The above Parking Brake button vs Speed Tests were performed with the original software/firmware ~37.x, iirc.

Tried it again over the weekend with firmware 50 and results are entirely different. It never beeps at me and from speeds between 45 and 10 MPH it never engaged the brake.

Conclusion: With newer firmware, stay off mountain roads with a [almost] fully charged battery.


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## Guest (Jan 21, 2019)

This is shocking. I don't know any vehicle that doesn't have emergency brake function (electronic or not).


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## JML (Jul 26, 2018)

I'm on 2018.50 and this is the behavior I observed.

On a safe street, at about 35 MPH I tapped the park button, and the screen came up and said something like, "Emergency Braking Applied," but the car didn't slow down. Then I tried pressing and holding the button, and the car slowed down with what sounded and felt like the rear brakes locking. That is exactly the same behavior I would expect pulling the handbrake in most other cars. Next question, can this be used for parking brake U-turns?


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## Guest (Jan 22, 2019)

It definitely can be used for U-turns and drifting on the snow. 
Though some more advanced manufacturers (Germans) refined this function to have ABS type non-locking brake action before standstill, and then full lock at speed zero.
Press and hold is the correct way for vehicle to respond as then it can be safely cancelled if still not at standstill.


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## Unplugged (Apr 5, 2016)

Bullwinkle J Moose said:


> >You're coming down a mountain road in your Model 3 and when you press the brakes, they go to the floor
> As mentioned above - the *first* thing to do in this scenario is to *pump* the brakes. Often there's enough fluid still in the system you can build up pressure by pumping.
> 
> That's always your first line of defense. Before trying any of the other more radical techniques.


Actually, your second line of defense should be to make sure your Model 3 is set to "Standard" or maximum regen. Unless your car not only loses the brakes (highly doubtful) but also loses power (even more highly doubtful), you should be able to come to almost a complete stop on any mountain downhill. At about 6 mph, you lose the regen, and you can apply the emergency brakes by holding in the park button.


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## Kinnay (Apr 18, 2018)

Did I miss it or no one mentioned how to use the emergency braking at all? You press and hold the parking button and it engage the emergency brake. You even see the red logo on the screen when you do.


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## Guest (Feb 15, 2019)

Every driver should know that before ever driving. Either handbrake, footbrake or a button.
You pull, push, press... and hold that until you stop.


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## garsh (Apr 4, 2016)

Kinnay said:


> Did I miss it or no one mentioned how to use the emergency braking at all?


It was mentioned. 


garsh said:


> Yeah, there's probably a way to activate the parking brake in an emergency. But I couldn't find anything in the manual. If someone doesn't mind being a guinea pig, try holding down the "park" button while driving at speed to see what happens. That would seem to be the obvious way to activate it to me.





MelindaV said:


> There is a "now you know" video (I think in their 12 days of Model 3 series) where they did just this. It brakes until it hits a low speed, then puts it in Park.


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