Tag Archives: trailer safety

Downhill Braking, Brake Fluid and a Disclaimer

Great Brakes!

These are brakes!

The drive from my home in Minden, Nevada to Convict Lake in California is due south all the way on U.S. 395. The old highway has been the north-south conduit through the eastern Sierra Nevada and Cascade Range since forever and still serves well. I navigated slowly through Gardnerville, Nevada and then on to Topaz Lake at the California border. Continuing south, I went through Coleville, Walker and then Bridgeport where the scenery was beautiful and all went smoothly.

I drove past the road to Bodie then climbed up Conway pass to 8,143’ with a little effort, then did the steep 1,100’ downgrade to Mono Lake which required some attentive use of brakes and transmission. Though this grade is challenging for anyone, there were no problems on this trip. There could have been which is why I’m sending off this article (please read the disclaimer at the bottom).

Going down steep hills with a load (e.g. a trailer) is a skill I acquired while driving semi trucks up and down the Sierra Nevada many years ago. I’ve gone up and down Donner Summit, Echo Summit, Sherwin Summit, and Conway Summit during night time snow storms and during clear days. They’re always dangerous when you are pulling a trailer.

I thought I should share some pointers with those of you who haven’t had the opportunity to be a professional driver of really big and very heavy trailers and  equipment.

#1: The first and main rule is to read the road ahead – well ahead. Look a ½ mile out all the time

#2: The second rule is to brake early, gently and steadily.

#3: Maintain the speed you’re comfortable with while going down the hill. Do not let the 15,000+ pounds of tow vehicle and trailer build up speed, to say 65 MPH, and then try to slow it down to 55 MPH while fighting gravity. That’s how the brakes overheat. First, before heading downhill, get to 55 MPH (if that’s what your comfort speed is for that hill) and stay there.

#4: Use the transmission and engine by selecting a lower gear or maybe two lower gears while going downhill. The brakes are like a credit card – use when needed, but don’t splurge as hitting the limit can be quite dangerous.

#5: Read the yellow diamond signs; this is part of Rule #1. The signs you ignored when you weren’t puling a trailer are the ones you need to read now. When it shows a truck swerving and says 35 MPH, you’d better slow to 35 or less. If a sign says 6% down grade ahead, you absolutely need to prepare to gear down and slow to your comfortable downhill speed – now, not when you’re doing 70 MPH on a 6% downhill grade!

On vacant roads, practice applying your trailer brakes to feel how they work. Reach down and gradually move the trailer brake lever until you begin feeling the trailer brakes work. Repeat this process once every trip to 1) ensure the trailer brakes are working, and 2) to create muscle memory in case your vehicle brakes fail and you have to use the trailer to stop you. Training is your key to safety.

Speaking of brakes, get yours checked more often than usual when you’re doing a lot of towing. Ask the mechanic to flush your brake fluid at least once per year as hydraulic brake fluid gets very, very hot when towing and begins to lose its ability to transfer pressure after repeated heat cycles.

The brake fluid heats up as do all the brake parts when the brake pads are doing their job of generating friction. The heat isn’t bad as long as it’s not excessive or maintained for too long of a time. That’s when the pads begin to stop generating friction and the brake fluid heats up beyond specifications and begins to boil.

The way you can tell if your brake fluid boils is pretty frightening – you push the brake peddle down and it just keeps going down… very scary! In extreme cases, if your brake fluid boils, and it will if you’re not careful about braking with heavy loads, get it flushed out of the tow vehicle’s brake system right away and fill with fresh DOT 4 fluid.

Brake fluid comes on four grades or specifications based on U.S. Department of Transportation minimum boiling point requirements, ergo the “DOT” level assigned.

DOT 3 is the lowest grade permitted and is most common in all cars and trucks built before 2006. It has a minimum dry boiling point (0% water) of 401 degrees Fahrenheit. It has a minimum wet boiling point (3.7% water) of 284 degrees.  Notice how little water needs to be absorbed for the boiling point to drop substantially.

DOT 4 fluid has a higher minimum dry boiling point requirement at 441 degrees as well as a higher wet boiling point of 311 degrees.  Most cars and truck built after 2006 use this type fluid.  It is frequently used as racing brake fluid with boiling points up to 600 degrees and beyond.  Due to its chemical makeup, DOT 4 absorbs water more readily and should be changed more frequently.

DOT 5 fluid is silicone based and is highly resistant to moisture, but its compressibility is lagging well below the DOT 3 and DOT 4 fluids which makes it unsuitable for street use.

DOT 5.1 is the final fluid specification which has a higher minimum dry (500 degrees) and wet boiling point (356 degrees), provides strong system pressure with minimal compression, and is more lubricating which makes this grade excellent for vehicles with ABS. It enjoys success in the racing arena as well so look for higher boiling point temperatures. DOT 5.1 is not compatible with DOT 4 due to their chemical composition, so if you want to use 5.1, have your technician flush the brake system and refill with 5.1 – don’t just top it off over DOT 4 fluid.

Flushing the entire brake hydraulic system is a regular service item and doesn’t cost much. Spending $35 to $50 for fresh ultra high quality DOT 5.1 racing brake fluid is cheap and your braking system will be way more protected against heat degradation than it is now.

Be careful out there.

Disclaimer: Thank you for reading this article. Do not take these references, tips or suggestions as fact. They are my opinion which I’m sharing publically. It is your responsibility to drive safely and ensure the vehicle you are using is maintained safely. This article is not to be considered training or guidance. I am not a certified driving instructor nor mechanic and am not responsible for your actions. Sorry, it had to be said.