Brake Fluid and Your RV or Toad–Keep Yourself Safe

If David Letterman could do a comedic “Top 10 Most Neglected RV Items” list, brake fluid would have to be near the top. At the same time, if you and the motorhome are headed down a 7% grade and you suddenly find you’ve neglected your brake fluid, well, you maybe could die laughing.

When you step on the brake pedal, brake fluid is forced down to the brake pads, causing the pads to come in contact with your vehicle’s wheels. The friction between the wheels and brake pads slows your vehicle down, and at the same time produces a huge amount of heat. Here’s the problem: If your brake fluid has water in it, 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. Another common, and expensive scenario is this one: Your brake fluid gets water in it. 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!

So what’s to be done? Keeping an eye on your brake fluid integrity is important First, don’t fail to check your brake fluid level. 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. 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. Instead, when you take the lid off, 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. And 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.

But lowering fluid levels indicate one of two things: First, you may be headed toward a “brake job,” as 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–not something to be toyed with–it should be repaired immediately.

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 4. A “four” rating shows a higher boiling point than a 3.

BEWARE that DOT 5 fluid has a whole different makeup than DOT 3 or 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. Additionally, ABS brake systems are NOT compatible with DOT 5 fluids.  Even if you don’t have ABS, “converting” to DOT 5 fluids are fraught with controversy and questions about “spongy pedal” problems. DOT 5 fluids will not absorb water–and if water gets into the 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.

If you ‘keep the cap on’ your brake system, does that mean you don’t need to worry about the fluid absorbing water? Afraid not. 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% 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 having a yellowish tint. If it looks muddy or murky, then yes, its definitely past time for replacement. But just because 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? First, 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 a way to test brake fluid. The simplest system is a test strip based kit. The 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 they sell a kit of 25 strips for around $40. Check out www.gwrauto.com/stripdip.htm.

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 can be a bit more complex. If you want to undertake the process, then follow the directions given in your vehicle’s shop manual.