Here is an article on brake fluids, just in case someone mixes Dot 5 with Dot 3 or 4 .
The Wickedness of Water
The typical RV hydraulic brake system is largely a pump and a series of valves. Brake fluid travels throughout a system of plumbing—brake lines—and under pressure from the brake pedal (and its associated master cylinder) forces other components to shove your brake pads into contact with your vehicle’s wheel drums or rotors. The friction between the pads and their associated dance partners slows your vehicle down, and at the same time produces a huge amount of heat.
Here’s the problem: If your brake fluid is contaminated with say, water, the heat of braking causes the water to boil, turning it into steam. Unlike brake fluid, steam compresses easily, and suddenly your brakes go spongy, or worse, quit working altogether. You’re now at the wheel of 35,000 pounds of steel, hurtling downhill, hoping you’ll find a runaway truck ramp in time.
That’s the worst-case scenario. A more likely, but nevertheless expensive scenario is this one: your brake fluid is contaminated with water. The water slowly corrodes brake system parts. You take your pickup in for service, and instead of simply replacing the brake pads and maybe turning the rotors, you wind up replacing something like an ABS hydraulic unit for $250—plus labor—plus replacing brake pads and turning rotors!
Checking Your Brake Fluid
Keeping an eye on your brake fluid integrity is crucial to preventing expensive damage, or even catastrophic brake failure. First, check your brake fluid level on a regular basis. Some manufacturers have made the brake fluid reservoir translucent, so you don’t need to pull the lid off to check the level. That’s good in some respects, as common brake fluid is hydroscopic, meaning it will absorb water. If you take the lid off the reservoir and leave it off, the fluid will actually soak up moisture from the surrounding air—not a good thing.
If you need to remove the lid for a look, inspect, then put the lid back on. If the level is low, you should add more FRESH hydraulic fluid of the same specification as is already in the system. Before “popping off” the lid, make sure you thoroughly clean any dirt or debris from it with a clean cloth. Keeping crud out of your brake fluid system is critical.
A drop in the brake fluid level indicates one of two things. First, you may be headed toward a “brake job.” When the brake linings begin to wear out, you’ll see a reduction in fluid in the reservoir. This will show up gradually. However, if you see a sudden drop in fluid, it most often indicates a brake system leak. Don’t mess around with a brake system leak, get it fixed right away.
Brake Fluids by “Flavor”
What about brake fluid specifications? You’ll find DOT 3, DOT 4 and DOT 5 rated fluids at the auto parts place. What should you use? Always use a DOT fluid rated equal to or higher than that which your manufacturer indicates. For example, if your truck, toad or motorhome specs call for DOT 3, use DOT 3 or DOT 4. A “4” rating shows a higher boiling point than a “3.” That doesn’t mean, however, that a DOT 5 is better than a DOT 4.
DOT 5 fluid has a whole different makeup than DOT 3 or DOT 4. The latter are glycol based, while DOT 5 is silicon based. While theoretically the two won’t cause adverse reactions if they meet up in your brake system, they still won’t mix properly. Additionally, ABS brake systems are NOT compatible with DOT 5 fluids. Even if you don’t have ABS, “converting” to DOT 5 fluids is fraught with controversy and questions about “spongy pedal” problems. DOT 5 fluids are not hydroscopic—they won’t absorb water. If water does get into your brake system, it will simply “slug” down to the lowest point in the brake system and mass together. The lowest point is typically in the brake caliper, a spot that gets plenty hot when braking. If water gets too hot, it boils, and brake effectiveness is out the window.
Just being careful about keeping the cap on your brake system reservoir isn’t enough to keep out water. Rubber brake line parts can actually pass moisture from the air into the brake fluid. One industry estimate says that for every year of service, brake fluid absorbs about 1 percent of its volume in water.
Can you tell by looking at your brake fluid if it needs to be replaced? Brake fluid is typically clear or has a yellowish tint. If it looks muddy or murky, then yes, it’s definitely past time for replacement. But just because brake fluid is clear or yellowish doesn’t mean it’s still “good.” At the same time, a darkish colored fluid isn’t necessarily “bad.” Really, there’s no way to tell by looking whether or not your brake fluid has absorbed too much water for safety.
What’s to be done? Always change your brake fluid at least as often as your manufacturer’s service schedule directs. If you take your vehicle in for service, most good brake shops—and a lot of good general shops—have ways to test brake fluid. The simplest system is a test-strip-based system. A strip is dipped in brake fluid and then compared to a color chart to determine levels of fluid contamination. Do-it-yourselfers, we couldn’t find an auto parts retailer that sells the test strips. However, one Internet firm says it sells a kit of 25 strips for around $40. Check out
www.gwrauto.com/stripdip.htm .
So before this article comes to a grinding halt, let’s review how you can keep your RV stopping safely: Check your brake fluid levels regularly. Change the fluid at least as often as your rig’s manufacturer recommends. Don’t use DOT 5 fluid in an antilock brake system, and don’t mix it with other types of fluid in a non-ABS system. Finally, when checking your fluid level, keep the lid off the reservoir only long enough to inspect the fluid.
CHANGING BRAKE FLUID
Can you change your brake fluid yourself? It’s not a difficult task, but it is messy and time consuming. Before ABS brake systems, changing the fluid was just an extended “brake bleeding” session. Rather than just stopping the process when all the air was bled from the system, you’d keep going, adding fresh fluid to the master cylinder until all the old stuff was pumped out of the brake cylinder you were working on. Then you’d move on to the next and repeat the process. With the advent of ABS brake systems, bleeding or changing brake fluid became a bit more complex. If you want to undertake the process, follow the directions given in your vehicle’s shop manual.
