Brake Failure! The Motor MythBusters Investigate an Old Theory
A car’s braking system is probably the second most important control system on the vehicle after the steering system (a case could easily be made for the opposite). So why would the Motor MythBusters want to induce brake failure on this 1975 Dodge Tradesman Van? Faye Hadley left the guys—Bisi Ezerioha and Tory Belleci—to bond over a shared love of vans while she scouted future myth testing locations.
Bisi—owner and builder of one of the world’s fastest minivans—enjoys the modern convenience and technology of the latest and greatest minivans. Tory likes them old-school—custom graphics on the side, interior decked out with piles of plush carpet, bubble-windows, full-size, the works. They do have some common ground: the 1983 cult comedy Strange Brew, where brothers Bob and Doug McKenzie try to save the world (and drink lots of beer).
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What does a Canadian cinematic classic have to do with myths about brake failure? This whacky caper introduced a new way for movie villains to sabotage a vehicle’s brakes. Instead of cutting the brake lines directly, the bad guys loosened the hydraulic lines just enough on the McKenzie brothers’ van so they would be able to complete two stops safely, then experience brake failure.
How do car brakes work?
Testing this myth is not as easy as it seems. Tory and Bisi can’t just crawl under the Motor MythBusters‘ awesome new ’75 Dodge van, crack the brake lines, and see what happens. In the movie, the bad guys’ plan works exactly as expected, but we’re pretty sure the MotorTrend Group insurance policy won’t cover Tory and Bisi intentionally crashing their van into a river.
Before the guys can start messing with the Tradesman’s brakes, they need to determine the minimum amount of brake pressure it takes to stop the old Dodge. A car’s braking system is basically a hydraulic pushing mechanism (master cylinder) that forces a high-friction material (brake pad or shoe) into contact with a flywheel (disc or drum brake) with the intention of stopping its rotation.
The closed system of master cylinder, brake lines, and brake caliper or wheel cylinder only work when there is enough fluid in the system to generate the required pressure. Remember, we told you before that liquids aren’t compressible, but gases (air, not gasoline) are. If a car’s braking system has an opening somewhere—say, if someone were to loosen a brake line or cut one altogether—then not only would the necessary hydraulic fluid be pushed out, but as the driver releases pressure on the system, air could get sucked in, making the brakes less effective on the next application of pressure.
Cracking the line for the perfect brake failure
Knowing they need to maintain enough pressure in the Dodge’s brake system for two full stops, Tory and Bisi now need to design a test to duplicate the myth’s conditions in the lab. But the lab isn’t the real world, kids. The Motor MythBusters are all trained professionals, with more trained professionals on the sidelines in case things go wrong.
Related: Braking System Basics
Things can go very wrong, very fast when you’ve got 4,000+ pounds of Dodge van riding on intentionally faulty brakes. Bisi and Tory also engineer extended controls to operate the van safely from the middle, far away from any hard surfaces like a dashboard or steering wheel they could bang their heads into upon a rough stop. Adding another degree of safety to those controls, they’ve included weak points in the extensions that will shear away and not push a hard, metal steering wheel or brake pedal into a soft, fleshy Motor MythBuster.
For this myth to be confirmed, Tory and Bisi need to loosen the fittings on the Tradesman’s brake lines just enough to be able to complete two full stops, then suffer complete brake failure on the third attempt at stopping. What a strange day at work, when crashing a Dodge Tradesman means the Motor MythBusters did everything right.
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