When they cut someone's brake line in the movies.

[atikovi]

Is that even a realistic way to make someone crash, or mostly theatrics?

1. All cars since the 60's have dual braking systems so if a line was cut, you would still have braking.
2. What about the emergency brake?
3. OK, so a bad guy cuts all the lines. As soon as the driver steps on the brake to put it into gear and the pedal goes to the floor, he's not going to drive it.

 

[supton]

1. I don't think that is true. I have lost a brake pad and needed to pump up a caliper, and it sure felt like no brakes when the pedal went to the floor.
2. Let's face it, in an emergency, our brains tend to be first to leave the situation.
3. Ya got a valid point right there. Ever since they put in that brake-shifter interlock (step on brake to shift out of park) one should have known right off the bat there was no brakes--might be in gear before you notice, but then you could slam back into park. [Usually I step on the brake to start a manual, so even more heads-up there.]

 

[spasm3]

My avalanche ruptured a rear brake line, I had virtually no brakes, I was lucky to get stopped, blew through a red light.

 

[Kawiguy454]

the trick is the "Cut" needs to be a pinhole. Then the brakes wont fail till you're on a cliff near the ocean. My 68 impala lost front brakes due to leak the rears still worked ...barely. Today methinks they will all fail if a leak occurs.

Another one that kills me is the Hollywood Hotwire. guy reaches under the dash, yanks out some wires then "Sparks" two of them to start the car and takeoff.

 

[Lubener]

Is that even a realistic way to make someone crash, or mostly theatrics?

1. All cars since the 60's have dual braking systems so if a line was cut, you would still have braking.
2. What about the emergency brake?
3. OK, so a bad guy cuts all the lines. As soon as the driver steps on the brake to put it into gear and the pedal goes to the floor, he's not going to drive it.

You forgot to mention it happens going down some steep mountain side.

 

[64bawagon]

Are you trying to say that Hollywood doesnt accurately portray real life experience ? Youre probably one of those Santa Claus haters too.

 

[Hall]

1) False - had a brake line rust through and I had no brakes. The "dual" system still shares a single fluid reservoir and it will empty that even though there may be a "dual" system in place.

 

[atikovi]

The "dual" system still shares a single fluid reservoir and it will empty that even though there may be a "dual" system in place.

No, there is a separation inside the reservoir to keep them isolated.

 

[PimTac]

We had a number of brake line cut incidents last year. It seemed to be the latest vandalism thing. Accidents occurred because of it.

 

[Lyman]

Why are you asking?

 

[Dave9]

There is supposed to be a partition to keep the two working, but I too, have had a leak in the rear and it effectively reduced braking to a fraction of normal (certainly not as high as 1/2 with front still fully working) , though I had already noticed diminished braking and the dash light, before it got that bad and was able to safely, slowly, drive home because once the rear had emptied, the front didn't get any worse, always kept a little braking.

 

[Pew]

Absolutely realistic. Not exactly cutting brake line but same affect (loss of fluid): my buddy had a leaking bleeder nipple on the driver front caliper when he went to the track and after a couple laps he lost all brakes . He was lucky enough to stop in the grass before hitting the crash barriers. E brakes are useless, as the manual level ones are too weak to stop a car at a 'normal' rate - I don't know how strong the electronic e-brakes are.

 

[Hall]

No, there is a separation inside the reservoir to keep them isolated.

There is supposed to be a partition to keep the two working, but I too, have had a leak in the rear and it effectively reduced braking to a fraction of normal

As I mentioned above, (1) of the (2) brake lines going to the rear brakes rusted/rotted out and I had next to no brakes. Each brake press got "worse" before I slowed down to 5-10 mph (I was blocks from home and able to navigate through side streets using the parking brake). This was a '99 Accord.

 

[nascarnation]

We had a number of brake line cut incidents last year. It seemed to be the latest vandalism thing. Accidents occurred because of it.

Man that's nasty. I always try and take a quick look for spots under the car but if it's dark or rainy or snowy you can't see much or anything.

 

[SoNic67]

1. All cars since the 60's have dual braking systems so if a line was cut, you would still have braking.

Absolutely not true. If one line of the four wheels has a leak, it will bleed out the single reservoir. Not instantly, but after a few brakes it will. That's actually how you bleed the brakes...
I don't know of any car with separated brake fluid reservoirs.

2. What about the emergency brake?

Most of the cars have parking brakes on a small rear drum, that barely keep the car still on an incline. The brake shoe is cheapest material, sufficient for static friction. At 80mph, that brake shoe will fade and glaze almost instantly. I glazed a few by forgetting the parking brake on and driving away.

The only cars that I owned, that didn't have parking brake like that, were Mercury Sable (Ford Taurus) 1996-2001. They had the parking brake applied by pressing a pedal (like trucks). That was activating mechanically a worm in the rear brake cylinder (disc brakes). They didn't have any "drum" on rear spindles. That car would NOT move with the parking brake on.
That could probably lock the rear wheels at high speed, but still, the braking efficiency dictates that 3/4 of the braking force is on front wheels, so the rears are not as big as the fronts.

3. OK, so a bad guy cuts all the lines. As soon as the driver steps on the brake to put it into gear and the pedal goes to the floor, he's not going to drive it.

Maybe he would feel the pedal going to the floor quicker. But maybe the bad guy cut the line just perfectly thin that didn't penetrate the metal. Just thin enough to resist some pressure, but not the pressure of a panic stop.
It happened on one of my cars that had the steel brake line rusted from inside. The brake line was coated with nylon. That could resist at pressing the brake pedal without engine running (no boost), so I didn't feel anything when I started the engine. But the next press, with vacuum boost assist, broke it and pedal went to floor. I was still in my driveway...

 

[eljefino]

I've lost half my brakes.

You have to also include the human condition. A brake pedal that you're used to being firm underfoot sinks to the floor. What do you do? Jump off it, pump it. I slammed my van in Park at 5 mph and the pawl clicked a few times before engaging. Yeehaw! I think if I had a handbrake in that van I'd have gone for it quickly-- I have the muscle memory of using handbrakes for uphill starts in stick shift cars. I have successfully used the handbrake to avoid rear-ending someone on an icy road when my brake bias was too far to the front axle.

If your brakes are in perfect adjustment you may get some usefulness out of the bottom 1/2 inch of pedal travel when it's in the carpet. It sure won't feel fun. You want to NOT pump them in this scenario, even though pumping feels better and it's what we were all taught to do.

On the flipside I've also lost a brake pad lining and 5x pumps of the pedal brought the metal backing plate in contact with the rotor and I had working, albeit loud brakes again. So when the pedal goes bad how do you know in an instant what happened and should you pump or not?

Side note-- the reservoir is not the brake fluid you use. You can shear it off and still have brakes. There's a pair of tiny pinholes in the top of the M/C that lead to the reservoir that let fluid drip down behind the piston when the pedal is fully up. A misaligned pushrod can block these pinholes then when the brake fluid expands from heat there's nowhere for it to go so it applies the brakes in a positive feedback loop.

 

[atikovi]

Absolutely not true. If one line of the four wheels has a leak, it will bleed out the single reservoir. Not instantly, but after a few brakes it will. That's actually how you bleed the brakes...
I don't know of any car with separated brake fluid reservoirs.

There is a separation within the reservoir on modern cars. Even on my '82 Vette where the master cylinder and reservoir are one piece.

If one line of the four wheels has a leak, it will bleed out one reservoir, but the brakes fed from other will still have braking at a reduced amount.

 

[manicrodder]

Is that even a realistic way to make someone crash, or mostly theatrics?

1. All cars since the 60's have dual braking systems so if a line was cut, you would still have braking.
2. What about the emergency brake?
3. OK, so a bad guy cuts all the lines. As soon as the driver steps on the brake to put it into gear and the pedal goes to the floor, he's not going to drive it.

Bad guy in the movies?? You can get that done for no extra charge at your local quick lube.

 

[Jetronic]

1) False - had a brake line rust through and I had no brakes. The "dual" system still shares a single fluid reservoir and it will empty that even though there may be a "dual" system in place.

have a close look at that reservoir, it's split in 2 at the bottom.... to all who had "no brakes"after a brake line failure... either you have too much carpet or you really didn't press deep enough. Half the brake pedal stroke does nothing, but after that you get half the normal brake power.

Picture of a divide in the reservoir:

 

[SoNic67]

have a close look at that reservoir, it's split in 2 at the bottom.... to all who had "no brakes"after a brake line failure... either you have too much carpet or you really didn't press deep enough. Half the brake pedal stroke does nothing, but after that you get half the normal brake power.

Same happened to my Ford Explorer when one of the lines leaked (rust pinhole). Pedal was going to the floor with no resistance, fluid was spurting out. That car has a split reservoir too.
I wonder if the ABS block makes a difference, because that's where the brake lines were actually connected.