One of the more memorable quotes from the movie Predator (1987) applies to the chore of bleeding brakes. This process, one of many that should be on the standard maintenance list, is often overlooked, continually postponed, or done only after brake repairs. It is not that it is a difficult task or one that consumes a lot of effort or time, but it, depending on the method, usually requires help. In my case, I often relied on friends or family to assist and, therefore, was always restricted to times when schedules matched. Martha likes to remind me that soon after we met, we spent a “date” occupied by this endeavor. She handled Big Blue’s brake pedal and fluid reservoir whilst I crawled behind each wheel and shouted “down”, “up”, “down”, “up” to her for half an hour as I opened and closed the bleeder valves. Now with kids, house, and other demands on free time, bleeding Moby’s brakes has only received fleeting moments of attention. The “I ain’t got time” excuse became the standard impediment.
Replacing the fluid throughout the brake system (a process known as bleeding the brakes) is essential for long brake system life and, of course, reliable braking action. Over time brake fluid absorbs water that causes rust to form within the system; blocked brake lines and leaky, frozen components like brake cylinders and caliper pistons are the result. In addition, water boils during heavy, frequent breaking or as the result of dragging brakes caused by restricted lines or frozen components. Boiling increases the pressure within brake lines and interferes with the function of the brake system, most often causing brakes to drag more, suddenly lock up, and potentially burn. Both rust and boiling can leave one with a terrible surprise when it is time to stop! Most recommendations state that brake fluid should be replaced every two years in order to flush the system of water and keep the brakes healthy. We have had Moby for three and a half years now, which means she was at least one and a half years over due (most likely even more as it is anyone’s guess when the PO flushed the system before we bought her). I had to make time to bleed before this year’s driving season.
There are several methods employed to accomplish this task. I have only experienced the first method which requires two people; one person to sit in the driver’s seat and man the brake pedal while keeping an eye on the brake fluid reservoir and a second person to manage the bleeder valves at wheels. The latter crawls under the bus, behind a wheel, and places a section of spare/old fuel line over the bleeder valve. This hose goes from the valve to a clear, stout container where its end is submersed in a little bit of fresh brake fluid. After calling up to the person sitting in the cab to push the brake pedal down as far as it will go, the bleeder is opened and the old nasty brake fluid flows into the container via the fuel hose while the brake pedal is continually pushed down. When the fluid stops flowing, the bleeder is closed and the brake pedal is released. The process is then repeated (“down”, “up”, “down”, “up”, etc….) until the brake fluid flows clean and free of air bubbles into the container. It is important for the person sitting in the cab to check the reservoir once in a while to make sure it always has plenty of fresh brake fluid and does not run dry. If they fail, the process must begun again to make sure there is no air in the brake lines. After the first wheel, the other three are completed in the same manner. All in all, this method is simple and efficient, taking maybe an hour at most depending on breaks to rest the leg pushing the brake pedal.
The second method requires a vacuum brake bleeder tool. These tools, which can be had at most FLAPS, are relatively cheap (~$20 and up) and eliminate the need for a second person. Due to our fairly busy family schedule, I decided to do a test run in the interest of being able to complete this undertaking in the hour I have before the kids get off the school bus. Below is a picture of the setup (I removed the tire for easier access, but doing so is not required). The basic principle involves generating a vacuum (around 10-15″ Hg) on the valve and then opening the bleeder so brake fluid will flow through the tube and into the plastic container. When full, the container is emptied, new fluid added to the reservoir, and the procedure continues until the fluid runs clear and clean out of the bleeder valve. Try as I might, I could never get a seal tight enough around the bleeder to hold a sufficient vacuum. The best result I achieved was a little brake fluid running out around the valve threads and dripping on the floor, a common problem I later discovered. Brake fluid is nasty stuff and should be handled with great care as it destroys paint, rusts metal, and renders brake pad surfaces useless. Obviously, I was not happy with the result and turned to focus on the third method.
The third method is outlined in the Bentley manual, along with the two person procedure mentioned previously. In this scenario, a pressure bleeder is used to pressurize the brake system from the reservoir end while simultaneously delivering brake fluid to the reservoir. The bleeder valves are then opened so brake fluid will flow through a tube and into a container. When the fluid becomes clear, the valve is closed and the next wheel begun. What makes this method appealing is that once the pressure bleeder is attached to the reservoir, one person is all it takes to bleed all four wheels, usually in about 15 minutes or less without interruption. “OK, I’m game.” I thought, “How much for one?” $150-800 +!!!
Here, my enthusiasm waned and my attention returned to the more traditional first method. Yet, I still did not want Martha and myself to kill a weekend morning or afternoon trying to bleed brakes accompanied by the constant interruptions of children running around dismantling the house (as they are want to do when they feel a sense of freedom). There had to be a way to test this pressure method while remaining financially secure. I thought a good solution lay in using my air compressor, but found that controlling the low pressures needed (10-15 psi) was difficult. In addition, I had no convenient method to attach the compressor to the brake fluid reservoir. I then turned to the all encompassing knowledge database, otherwise know as the web, for help. Turns out people have thought about this issue before!
The web produced a product sold by Motive Products designed for the job at hand. This device is based on a pressure sprayer type apparatus which can both deliver brake fluid and pressure simultaneously when flushing the brake lines. Reviews indicated that the ~$60 is money well spent, but, after failing with the vacuum bleeder, I wanted personal verification pressure bleeding would work. Besides, I already had an old, long since retired hand sprayer so why not try to build my own? Turns out, people have thought about this too! This website was particularly helpful in devising a way to hook the sprayer up to the reservoir. However, there were no appropriate aftermarket reservoir caps at the FLAPS around here (the one mentioned on the website will not fit bay window reservoirs), but if one plans far enough ahead, replacement caps can be ordered through VW parts vendors. If you are cheap like me and do not want to spend $5 shipping on a $1 part, you can use the cap from a quart oil bottle (clean it thoroughly first). Below is the photo record of pressure bleeder construction and its use, along with some notes/tips. I will probably make some changes in the future (like adding the pressure gauge and correct reservoir cap), but this was a very successful first run. This method is indeed easy and fast, so no longer is the “I don’t have time” excuse valid – everyone has time to bleed.
A couple of notes: 40 year-old plastic is brittle and, on buses at least, there is no clamp on the tube between the upper brake fluid reservoir and the lower master cylinder reservoir in dual-circuit systems. Recommendations keep the pressure at or below 10 psi to avoid damaging weak components. Never use pressures higher than 15 psi or the master cylinder might be damaged as well. Brakes should also be bled in a certain order. Although the most common thought starts with bleeding the rear passenger side brake, then the rear driver side, moving on to front passenger, and then finally front driver side, Bentley and a few others state dual-circuit, front disc systems can be bled: front passenger, front driver, rear passenger, and rear driver side. I have always done the former and found no need to change at this point. DOT 3 or DOT 4 brake fluid meets the standards laid out in the Bentley manual. I found some discussion on using silicone based brake fluid which will not absorb water. However, it seems that water still accumulates within the lines and forms masses that still cause rust, will boil, and, consequently, need flushing on a regular basis.