How far could you drive if your brake lines were cut?

Factual Questions
1

So, one of my characters sabotaged the car of another’s parents. They got into a crash and both died when they failed to stop at a red light. I’m not married to the idea, but at the moment I have grandpa confessing to having cut their brake lines.

Realistically, how far could they drive before they realized there was something wrong with the brakes? Would this have to happen fairly close to home (they’d know the first time they tried to brake?) or would they work at all at first? I’m thinking they wouldn’t work at all based on how quickly I realized there was a problem when I my brake line rusted through - as soon as I put my foot on the brake before reversing, it went to the floor. It was a pretty large hole, however.

This only matters because he’s disappointed that the other character’s parents died before picking him up from school. I’m wondering if maybe he shouldn’t be disappointed, at least not if he had any idea what he was doing when he set them up.

And when we say someone “cut” brake lines, that isn’t meant literally, is it? Isn’t it more along the lines of punching a hole in them so the fluid drains out?

2

I generally step on the brakes before shifting out of park when backing out of the driveway.

A big leak would show up fairly quickly. A small leak would almost certainly give itself away some time before total failure. Which is why people with leaky brake lines are not constantly smashing into trees.

3

Depends on the driver too, if they’re savvy enough to gear down and/or use te E-brake. I’ve driven cars w/ no brakes for several miles w/o a problem. Even w/ a small leak you’d notice a difference pretty quickly, then it depends on whether the driver is experienced enough to recognize the potential danger.

4

The trouble is that the fluid won’t leak out of a small hole unless you press on the brake, and then you’ll feel it getting mushy. A big hole will leak it all out before the person gets in the car, and the dead brake will be pretty obvious right away. What you really want for your story is for the brake to appear functional when they get in the car and start moving, then have all the fluid leak out, and the brakes totally non-functional once they get to speed. I don’t see how that’s possible by simply damaging the line. I think the whole cutting of the brake line as a method to murder is a hollywood fantasy.

5

How about a time delayed detonation. It need not be a big one. :smiley:

6

Brake lines come in two forms - metal piping, and reinforced rubber hose. Either can indeed be cut, the former with a hacksaw or tubing cutter, the latter with a knife. Punching a hole isn’t really feasible. It would require using a hammer and punch or awl for the metal lines, and aside from the logistics problem of finding room to swing the hammer it would likely flatten the line before piercing it. The rubber lines could be pierced with an awl, but since they’re reinforced that’s more difficult than slicing them with a knife.

As far as trying to precipitate a crash, it could be done (and I imagine has been done) but it’s not as easy as fiction makes it sound. If a line is cut all the way through, it’s going to be quite noticeable on the first application of the pedal. On a car with an automatic tranny, that’s while sitting still shifting out of park.

One way to get around that would be to create a small leak with the hope it wouldn’t be noticed before the fluid got low enough to result in no response to braking. An alert driver might notice some give in the brake pedal, but I could see it getting by some people. But usually fluid will drip out of the leak just sitting there, so the size of the leak and the time between creating the leak and the car being driven would have to be coordinated.

The other way would be to cut the line nearly all the through so as to leave a weak area which would hold for a while, or for normal braking, but suddenly give way, particularly during a panic stop. The trick would be cutting just the right amount, which is quite a challenge without X-ray vision.

In either case, it could be effective in old (pre-70’s) single circuit brake systems, where a leak anywhere affects the whole system. In modern dual-circuit systems, it’s tougher. While losing one circuit can cause a noticeable decrease in braking, it doesn’t cause a complete loss. Getting both circuits to fail simultaneously would be nigh onto impossible.

In sum, if a line is cut through, a driver would have to be pretty clueless to not notice it on the first application of the brakes. If it has a small leak it would usually be detectable while being driven. A not-quite-through cut would not be discernible to the driver, but requires careful execution to do right and depends on luck for the failure to happen while approaching, say, a stop sign at a busy intersection rather than the back of another vehicle stopped at a light.

7

Just as a personal example we had some mice that took up residence in our garage last winter. They must have had a liking for the taste of brake fluid since they gnawed through my wife’s brake line on her new RAV4.
Backed out of the driveway fine and braked, drove to the end of the block to a stop sign, hit the brakes and rolled out into the intersection. There was no other cars but if there was she would have been hit by another car going 35 mph.
Certainly no firey death but not pleasant.

8

Since nobody has made the snarky comment yet… :smiley:

You could drive as far as it takes before you have to use the brakes for the first time.

9

Or to quote Rom White:

“All the way to the scene of the crash.”

:smiley:

10

I got only about three blocks when it happened to me.

11

Perhaps you’d be better off if some futzed with the physical linkage from the petal to the brake master cylinder. May loosening it so that it will fail later, or maybe replacing part of the linkage with something that will break upon hard application of the breaks. This would be the only sure way to have a 100% failure that wouldn’t be noticed before it happened.

12

The best way to produce a hole is to cut the line with a hacksaw. You saw until just a small leak is there, and stop cutting. Without power assisted brakes they won’t lose much fluid until they force out the fluid by depressing the brake petal.

You can still use the parking brake to stop. You need to be careful, as to not lock up the brakes.

13

Definitely an argument for some practice in using the emergency brake. It seems that people who don’t practice this often don’t think of it when a problem happens.

14

Well as has been stated any car built past 1968 has dual circuit masters, which should (but don’t always) retain some braking power when one circuit is lost. I have seen cars that did not have any pedal when one circuit was DOA.
Now if your plot allows for the people to have a delayed accident, the addition of a substance that is injurious to the seals in the system, will cause a total failure of the system given time. You can also add a substance that lowers the boiling point of the fluid. Brakes get used hard, brake heat up, fluid boils. Gas pockets = No brakes.
I don’t feel comfortable posting the answers here, but suffice to say, what I am talking about is common, and in both cases, brake failure will occur.
Feel free to PM me or send me an e mail, and I will supply the answers.

15

That’s good to know. The accident in question would have taken place around 1984, so I suppose should figure out if a car from then is likely to have had power brakes. I know my parents said our car then didn’t, but it was quite old.

Joey P’s idea sounds less chiched though, doesn’t it? I haven’t given Grandpa an occupation, so maybe he could be a mechanic, which would explain how he was able to do something more complicated that cutting their brakes.

16

have you ever tried to stop with the emergency brake? she would have wound up in the street anyway.

if your brakes fail like hers did your best response is to pump the pedal like mad and try to get some pressure back up WHILE taking evasive action. like trying to take a right (the safest move as a general rule)

brake failure blows arse and is fortunately rare as hell these days.

With a complete cut you wouldnt even be able to get out of the driveway. you cant take the car out of park unless the brake is on. (not sure how far back this goes but I believe its from the 70’s)

you would be better off with some kind of timed way to cut all the lines at once or maybe even go after the master cylinder instead. take out that and you are brake less for sure.

17

With or without power brakes you won’t lose much fluid until the pedal is pressed.

18

For automatics, yes. Manuals have no such requirement. They also have no “Park” transmission position.

19

Aside from the application problems, it’s a pretty iffy way to kill somebody. Even if they do lose their brakes at high speed there’s a good chance they’ll be able to stop the car without getting into a fatal accident, even if the e-brake is damaged beforehand. The intersection they’re approaching may be clear, in which case they could just coast through it and ease onto the shoulder. It doesn’t seem like something an intelligent character would try even if they could get the timing right.

I’m not trying to be a literary critic here, just sayin’. :slight_smile:

20

dont get me wrong the ebrake will work but usually takes 2 or 3 times as long to stop (if not more) since it only affects the rear brakes. so in a situation like a stop sign or red light you usually get one hell of a surprise.

missed the edit window :frowning: