You may have been told that due to an anti-lock brake system hydraulic controller. If those get air in them, it can be impossible to remove without using a very expensive scanner.
The only thing you need to worry about is to not allow the brake fluid reservoir to run empty. That way no air can make its way down to the controller. Start out by looking at this article:
https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system
Now allow me to add a few comments of value. It is a good idea to replace the brake fluid every few years, but flushing isn't necessary. Every manufacturer has a recommended interval, but very few of us follow that because this system causes such little trouble.
One thing to watch out for is brake fluid must never become contaminated with a petroleum product such as engine oil, transmission fluid, power steering fluid, axle grease, or penetrating oil. Professionals even wash their hands with soap and water before handling parts that will contact brake fluid, to avoid getting fingerprint grease in the brake fluid. Petroleum products, even a few drops, will cause rubber parts to swell and become soft, slimy, and mushy. The rubber lip seals in the master cylinder will grow past the fluid return ports, blocking them and causing a brake drag, or locking brakes. When the system has been contaminated, there is only one proper repair. That is to remove every part that contains a rubber part, flush and dry the steel lines, then install all new rubber parts. That includes calipers, wheel cylinders, rubber flex hoses, the master cylinder and reservoir cap with its rubber bladder seal, the combination valve, if used, (it is near the master cylinder with the two steel lines running to it), and when used, a height-sensing proportioning valve. Those are mainly a minivan and pickup truck thing because they can have such a wide variety of loading, front to rear. If the vehicle has anti-lock brakes, the hydraulic controller must be replaced too as it has rubber o-rings in it. If any rubber part is not replaced, the contamination will leach out of it and recontaminate the new brake fluid. This gets to be a very expensive repair.
For the regular brake fluid replacement, all that's needed is you must be able to open the bleeder screws on the calipers and wheel cylinders. If one or two are rusted tight, rounded off, or broken off, I would just disregard bleeding at those wheels. You won't ever get all the old fluid out, and the new fluid will work its way around eventually. The reason for doing this procedure periodically is brake fluid absorbs moisture out of the air, including through the porous rubber flex hoses. That moisture promotes the corrosion of metal parts, leads to a buildup of debris behind the pistons in calipers, and most importantly, it lowers the fluid's boiling point from well over 400 degrees to near 212 degrees. Under normal braking, the fluid will get hot enough for that moisture to boil and turn to a vapor. That causes one form of brake fade or a low, soft brake pedal.
Another thing to watch out for is when bleeding brakes, there are a number of ways to do it. A lot of competent do-it-yourselfers use pedal-bleeding, and even some service manuals will tell you to push the brake pedal all the way to the floor. That absolutely must be avoided unless the vehicle is less than about one year old. Crud and corrosion build up in the lower halves of the bores in the master cylinder where the pistons don't normally travel. Running the brake pedal to the floor runs the rubber lip seals over that crud and can rip them. That results in a slowly sinking brake pedal that often takes two or three days to show up. That requires a replacement master cylinder. If it comes to that, let me know before you start the job. I have a trick that prevents needing to bleed at the wheels. Never push the brake pedal more than about halfway to the floor to avoid this heartache.
Some people will use a hand pump or air-powered vacuum bleeder with a hose attached to a bleeder screw. That can get the job done faster but the tools are not a good value unless you'll use them often. Keep an eye on the reservoir so it doesn't run empty. If you use this with a clear hose that they usually come with, you'll see a constant stream of tiny air bubbles coming out with the fluid. That is not due to air in the system, and they'll never go away, no matter how long you bleed. That air is being pulled in past the bleeder screw's threads, and can be ignored. Air coming out with the brake fluid will appear as long bubbles or gaps in the flowing fluid.
When you add brake fluid to the reservoir, pour it from can that was sealed, again to prevent it from absorbing moisture. If you need to use a funnel, be sure it is clean and was never used for oil. Many years ago, a Sears store in California had to pay for repairing over a dozen vehicles after their brake "bleeder ball" was refilled with a funnel that had been used for engine oil, then was wiped out and used for brake fluid. That was just a little residue going into a tool that holds over four gallons of brake fluid.
That bleeder ball is another method of bleeding that we don't need to discuss. It's an expensive tool only used in shops that have a use for it multiple times per week. It forces brake fluid into the reservoir under a few pounds of pressure to speed up the process.
The only bleeding method I've used for the last 30 years is simple "gravity bleeding". Just open a bleeder screw or two, allow the fluid to drip into a container if you want to avoid making a mess, and loosen the cap on the reservoir so no vacuum builds up as the fluid leaves. Fluid flow may even stop completely if the vacuum in the reservoir builds high enough.
If the fluid doesn't start running out on its own, or it's flowing too slowly, you can "irritate" the brake pedal with your hand, but you only need to push it an inch or two.
Rather than waiting for all the old fluid to run out of the reservoir, you can speed this up by using a clean turkey baster to suck out most of the old fluid, then pour in the new stuff right away. If you allow most of the fluid to run out of the reservoir before refilling it, you'll be better able to keep track of how much you're replacing. If you go through two 8 ounce bottles of new fluid, consider the job done.
A lot of older ABS systems use a hydraulic pump and an "accumulator" to store brake fluid under very high pressure. I have a '93 Dodge Dynasty with one of those systems. It provides the power assist along with the anti-skid function. With the ignition switch off, the brake pedal with that system has to be pumped a minimum of 40 times to drain the accumulator and lose the power assist. The fluid goes back into the reservoir and the level will just barely reach the cap. At that point all that fluid can be sucked out. New fluid must be filled to the same level before the ignition switch is turned on. That's when the pump will run and put fluid back into the accumulator. This is an easy way to know exactly how much new fluid to add. Fill the reservoir to the top, turn on the ignition switch, wait up to a minute for the accumulator to charge up, and you're done. I replaced one bottle of fluid last year, for the first time since the car was new. It will turn 5,000 miles this coming summer. The brake fluid hasn't been hot very much, but it's a time thing that allows moisture to be absorbed into the brake fluid.
A lot of pickup trucks in the 1980s and '90s had a rear-wheel-anti-lock brake system. Those used a "dump" valve on the frame rail, right under the driver's feet. You treat those just like a regular piece of steel line. They're open to fluid and air flow like normal, all the time except when they're trying to stop a skid. No special procedures or tools are needed to bleed those systems.
If the brake fluid leaving a bleeder screw changes from dark brown, which just means it has been hot at times, to clear, you have new fluid all the way through that circuit and you can close that bleeder screw. If the fluid never really becomes clear, that's to be expected. The old and new fluid typically mix as it works its way to the bleeder screw, and color changes are hard to see. If you get three or four ounces out at any wheel, roughly half a small bottle, you can consider that sufficient.
If the reservoir does run empty but you catch it right away, you may still not need to bleed the ABS hydraulic controller. Same is true if your car doesn't have anti-lock brakes. Close all the bleeder screws, add fluid to the reservoir, then slowly work the brake pedal multiple times. Push it less than halfway to the floor very slowly. That will push new fluid down the lines while any air floats back up. Release the pedal quickly. The brake fluid rushing back will wash any air bubbles back with it into the reservoir. Just a few pedal pumps will work the air out of the lines. If you have a helper do this, you can usually see the air bubbles coming back into the reservoir. Don't worry if a few bubbles remain in the lines. You'll never notice that in the brake pedal, and that air will not go further down. It floats up. Every time you're sitting at a red light with the engine vibrating, the air will tend to work its way up, and eventually reach the reservoir when you release the brake pedal.
Let me know if I provided enough information or if you have other questions. Also let me know how the project turns out.
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Tuesday, January 24th, 2023 AT 1:31 PM
