By Greg Illes
Absolutely everybody changes their engine oil and transmission fluid (or has it done). Some folks remember to change differential gear oil. But who ever thinks about changing brake fluid? We all should.
Change brake fluid — Huh? Why in the world would you want to do that? True, there are no grinding gears or slipping clutch plates in your brake system. But there are high temperatures, and there is a hidden secret in that fluid — it attracts water. The temperatures cause the system’s fluid to expand and contract slightly and this “breathes” tiny amounts of air in and out of the fluid reservoir. Over the course of time, each tiny puff of air contributes a small amount of water vapor which is absorbed into the fluid and circulated throughout your brake system.
Since water is as uncompressible as the brake fluid itself, you cannot tell from pedal pressure or system performance that the fluid has been compromised. But your system components can tell. That water starts to work its way into coatings and platings, starting the insidious corrosive process that can eventually ruin cylinders and calipers.
The only way to rid your system of the water is to completely flush the brake system with new fluid. This is very different from simply topping off the reservoir, and it’s not the same as emptying and refilling the reservoir. Flushing involves “bleeding” fluid from each and every wheel cylinder and pumping fluid through the system until fresh, new fluid flows out of the bleed valve.
The process is laborious and messy, and generally can require either two people and/or specialized equipment. Although I’m personally quite handy and do most of my own maintenance, this is one job that I leave to the pros. It will typically set me back about $100 or so.
A “brake job” is part of normal maintenance and will ordinarily consist of replacing pads or linings, turning drums or rotors and, of course, a thorough system inspection. By periodically flushing the brake system fluid, you can help to insure that a routine brake job doesn’t end up involving costly replacement of corroded cylinders and calipers.
Since it’s time and not mileage that corrupts the fluid, the typical recommendation is for flushing every two years. Most of us have our rigs in the shop at least that often for one thing or another, so it’s easy to include the brake flush and not have to make it a special visit.