Since about 1969, all cars sold in the USA had to have dual barking systems (a master cylinder with two circuits, such that a leak in one would still allow for a parallel system to work).
Has anyone analyzed crash data to see it this saved any lives? I cannot imagine anyone driving with a leaking brake system-of course there are cases when a failure could happen immediately.
I’d say almost certainly, although many cases may have gone under the radar. Not all accidents are analyzed to the detail of checking the brake system function, and faulty brakes could be masked by crash damage. But logic alone tells us that the total failure allowed by a single-cylinder braking system will cause more accidents (and thus some greater proportion of injuries and deaths) than a dual-cylinder system that can remain half-functional even with catastrophic failure in one circuit.
I’ve had cars have failures in one circuit - usually slow leaks leading to very little effective pressure on those wheels. I was fortunate enough to be aware of the problem and cope/repair it before it caused an accident. Had all four wheels been affected, at least some of those faults would have led to an accident or at least some very hairy moments.
it’s not just that they’re dual circuit, it’s that they’re diagonal as well; meaning one circuit feeds the left front and right rear wheel, and the other feeds the right front and left rear.
A doberman and a rottweiler. Guaranteed no will break into your car.
I believe some earlier ones were front-rear. Maybe those predated the 1968 mandate.
Yeah, I was going to [del]bark[/del] snark about that, but I just had a 165-pound loss in that department and it’s not funny right now. Maybe next week.
I doubt I was in danger of actual death, but I had an incident where dual braking saved me from a crash in my pickup truck.
I had my truck loaded with lawn care equipment and pulled away from the curb to go down a residential street. About a 1/2 block later I braked for a stop sign… and my foot hit the floor with no resistance and the truck wanted to keep going. The second brake circuit brought the truck to a halt before I bumped over a sidewalk and into a wall.
Sudden break in the brake line, probably triggered by a bump in the road. It’s an old truck, there are some corrosion issues. I try to keep up with them but no one is perfect.
So, yeah, I’m pretty sure somewhere along the line the dual braking systems have saved lives even if they haven’t entirely prevented accidents. I don’t know if anyone has formally studied the issue. It’s not like I reported my problem to anyone, I just got the truck to a mechanic and got the brakes fixed.
Some cars have dual-diagonal braking, but the majority use a front/rear split. It has to be front/rear on disc/drum systems.
Am I wrong in thinking that diagonal would actually be dangerous? I mean, I’ve been made to believe that front brakes provide more of your braking power than the rears, so in a diagonal scenario, you’ll pull towards whichever side has the front brake. Front/rear, at least the braking will be even on both sides.
Surely, the cases you’d want would be the ones where there wasn’t a crash? Driver has to slam on the brakes, one set fails, but the car still stops in time because of the other one, so there’s no crash investigation.
No stats just anecdote —
I had a car old enough to have a single master cylinder for the brakes and it did make me nervous; I knew enough about the plumbing of my brake system to know of several possible point of fluid leak and/or pressure failure including
• an actual hole in the flexible line or the aluminum fixed lines (air in lines and/or fluid loss)
• brake cylinder seal failure (seriously fast fluid loss)
• drum brake spring-apparatus mechanical failure (potentially allowing brake pad to twist out of position & let brake cylinder expand past limit = gushing fluid)
• failure at the master cylinder seal itself (air, failure to compress fluid, fluid loss etc)
I bled my own brakes and replaced brake pads and repaired frayed hoses and so forth back in those days ($). I knew more modern cars had two master cylinder reservoirs (one for front and one for rear; the diagonal configuration came later I think). The idea that if you did have a leak or pressure loss, you’d still have braking ability via the second reservoir and associated system was enticing enough that I wanted to upgrade (either 3rd party replacement or buy parts from same make and model of a couple years later vintage and see if I could make them fit).
This is just the kind of question for the Freakonomics guys.
Sorry for your loss. I know how they are family members and how empty it is without them.
Well, right, so there should be a drop in the sorts of accidents that might be attributed to brake failures after the introduction of dual circuit brakes.
I think the statistical problem is that the introduction of dual circuit brakes was coincident with the introduction of front discs, which at least in my mind seems like the bigger improvement and would also reduce the same sorts of accidents.
You’re right, but here’s the other side of the coin: if the front system fails, there’s only about 30% of the braking force available with an increased chance of skidding. If half of the diagonal set-up fails, the steering has to be controlled but 50% of braking force is available. Neither way is perfect and some engineers choose one while some choose the other.
And now we need something even more fool proof.
Drivers are more & more driving in such a way that needs almost perfect brakes to avoid crashing into something/one/whatever.
I have driven things with mechanical brakes/no brakes, etc…
Learning that, makes a fellow drive different and I mostly can afford to not get into the mad dash to work stuff.
What is the first thing a kid does when the come to a guard rail? Manny manny adults are still kids in those kinds of ways.
I’ve had the brake failure too. No fatality, but a dual-cylender system would have saved money.
Put the brakes on, foot went to the floor, ran into the back of the car in front of me. Old car, but fully maintained.
In Aus, traffic fatalities are way down. Down so far that they’ve started reporting national fatalities, instead of state fatalities. Most of that is attributed to safer cars. the rest to safer roads and drink-driving restrictions. None of it is attributed to better drivers…
I wouldn’t think that safer brakes make up a big part of that, but man, cars are a lot more expensive to fix now than they used to be.
I’ve encountered a few Rottweilers over the years, and most of them were as friendly and gregarious as any doggies I’ve ever met. I’ve encountered the occasional Doberman, and they were all fairly friendly too.
Then there was the belt + suspenders solution that Volvo used on the 140/240 brake systems. Two independent circuits in each front caliper and each circuit had one rear brake. Lose a circuit you have both fronts and one rear left.
Apparently brake failure was the cause of 1% of the road toll (deaths) in 65…
now 0.00%
Which references “Lave and Weber , 1970”.
Just last week I was driving out of a parking lot(gentle slope downhill), when my rusted rear brake line burst and started jetting out brake fluid with each push of the brake pedal. It wasn’t really an emergency situation, but my reaction was interesting, and could shed some light on whether or not dual line master cylinders save lives. Although obviously at slow speeds death would be unlikely regardless.
In the first attempt to stop, the brake pedal felt spongy. I released it completely and on the next push it went down to the floor. Despite me being vaguely aware that even when the pedal is floored, the other brake line should still be working to stop the car, it didn’t actually feel like it was. I felt like I had maybe 10% of the ability to stop as I did only a few minutes ago, and I chalked that up to the brake fluid retaining a small amount of pressure while the fluid squeezed through the hole in the line. I ended up pumping the brakes and coasting to a stop, which may or may not have been faster to stop than just holding it on the floor. Perhaps someone with a bit more mechanical knowledge could tell me whether it would be faster to stop flooring the pedal or pumping it with only one hydraulic line working.
Afterwards, I tried to tell the tow truck driver how I thought that the dual system would have helped me slow down more and he flat out insisted that they didn’t even exist, which I’m sure is the general public ignorance.
Needless to say even with advance knowledge of braking systems, humans behave irrationally when they panic and without the feeling that any braking is actually happening they could abandon the brakes entirely in emergency situations, like in the classic ‘they didn’t even slow down before going off the road’ scenario. I completely forgot about my gears when trying to stop. I hope at a higher speed the system would have been more effective, but at the speed I was going I would equate it to dropping down to first gear when driving an automatic with that option.