If you’re not a car buff, the notion of a, “master cylinder” might not immediately scream, “brakes” for you. But the master cylinder on a vehicle is the place where brake fluid goes. It’s the plunger mechanism that converts pressing the brake pedal into hydraulic pressure that applies the stopping power.
The master cylinder is also where the reservoir(s) for the brake fluid itself reside(s). There are many nuances of braking systems, varying from power brakes vs manual brakes, disc vs drum, and these days even regenerative brakes on EVs. But sometime in the early 60s (I think, I couldn’t find an exact date), master cylinders switched from single reservoir to dual reservoir. It was for several reasons, but the most important was the safety it offered.
See, with a single reservoir master cylinder, if a brake line were to break or get cut, all the pressure created when stomping on the pedal would cause brake fluid to squirt out of the break or cut in the line. And if all the brake lines are connected to one single reservoir in one single hydraulic system, it would mean little to no pressure used for stopping the car. Many folks would refer to the single chamber master cylinder as, “suicide brakes” — because there was no redundancy.
Dual chamber master cylinders usually come with two different size reservoirs. This is because for a very long time, the back wheels used drum brakes, and the front wheels used disc brakes. (The disc brakes generally required the larger amount of fluid) But arguably most important was the separation of the front and back brakes hydraulic systems meant that if one system was compromised due to a break or cut, the other wheels weren’t affected, and the car could still stop. Thus the term, “suicide brakes” when referring to the old system with only one chamber.
Now, that’s an oversimplification. Modern cars actually have a single reservoir for adding fluid, but there are still two chambers in the master cylinder, keeping the front and back hydraulic systems independent, even though they are all disc brakes these days. (except for EVs, I have no idea what those magical unicorns do)
On Saturday, when Donna and I were driving home with my truck, in the middle of a blizzard; and the brake pedal felt a bit squishy, it was disconcerting — but not terrifying. My truck has 4 wheel disc brakes, and if indeed a brake line broke (which is usually what causes a brake pedal to get squishy in a modern vehicle), it was bad, but even during the blizzard, we’d likely be fine as long as we realized our braking ability was probably significantly reduced. We’d get home, cuss a bit, and then take the truck in for brake work once the blizzard was over. (I don’t have a garage, there’s no way I’m replacing brake lines in the winter outside)
And we did technically make it home safely, but it was just barely. And I mean just barely. See — while I haven’t been able to get to the truck to look under the hood (blizzard: truck is buried now), as soon as we turned down our road, the ENTIRE master cylinder gave way, shot brake fluid all over the hot engine (we could smell burning brake fluid), and completely stopped stopping the truck.
Brakes aren’t supposed to fail so catastrophically anymore, because the dual hydraulic systems are designed to keep your brake pedal working somewhat when you have a break/cut. So apparently the part of the brake system before the dual chambers (the plunger bits that convert pedal pushes into hydraulic pressure, most likely) just completely broke in epic fashion. Thankfully, we were already on our road, and going quite slow.
I managed to get the truck up our VERY steep driveway, and put it into park. We went inside, cussed a little, did a quick prayer of thanks, and moved on. The next day, I had to move the truck to get to the car parked behind it, and when I pulled it down the steep driveway, sure enough, there was NOTHING to slow the truck down even a little. Well, except for the snowbank across the street. (I was prepared for that, but still, it’s freaky to experience)
Now my truck is back up the driveway, all the way in the back, and buried in another snowstorm’s leavings. It will stay there until Spring, because like I said earlier, there’s no way I’m going to work on the brake system of my truck in the winter, in our gravel driveway, OUTSIDE.
So, how was your weekend? 🙂