Brake Bleeding Methods

Thank you for your explanation and diagrams Kiril. Very nice. It's a very long time since I've bled brakes but I want to resume because I have some time and I'm not happy with the way I see most mechanics approach jobs on my vehicles. I did a lot of searching and eventually came across your post while searching for 'cons' associated with bleeding brakes. I'm not comfortable with reverse bleeding because the fluid flow is 'opposite' to the working flow [although I know the fluid really goes forth and back] and so contaminants could flow back up to the reservoir. I prefer the vacuum method, but I can't think of a way to prevent air getting in through the bleed port? Is there? Thank you so much.

I have used manual, vacuum, gravity and pressure. Vacuum bleed works great for fluid transfer of vehicles that have been serviced regularly. Gravity is great to use in cases of doing wheel cylinders one at a time while, a lot of wait time though. Manual bleeding, the oldest form with gravity, is great but can cause issues with an older master cylinder. Pushing the pistons further than normal travel can cause debris build-up and damage to cup seals. Pressure bleed has been the go to for quite some time. Especially since ABS systems should also be put through an automated bleed procedure. I have yet to meet anyone enthused of the idea of RFI.

Wow great information Kiril! I was surprised to see such useful content on LinkedIn. Here in Canada we use a variation of the pressure method where the foot pedal is used to pressurize the system rather than an external pumping device. The brake pedal is used to push out the old fluid and air. To do this we simply: 1. Loosen a brake bleeder screw, pump the pedal to push the old fluid out, then add new fluid during the pumping to ensure the reservoir is not emptied during this step. (Gravity can be used to drain the system too..... if you have a sore leg or you have no assistant :) ). 2. Once we observe new clean fluid coming out of the drain hose attached to the bleeder, we shut the bleeder closed. 3. We then have an assistant pump the brake pedal a few times to build up pressure and hold the pedal in. 4. With the assistant holding the pedal down, we then quickly open and close the bleeder to squirt out any remaining air. The fluid is squirt under pressure as the brake pedal moves forward to the floor so the open and close period is only ~ 1sec or less. 5. This last step is repeated a few times until the ejected fluid is observed to be free of bubbles in the drain hose. I'm sure you know of this as it seems to go back many years. I just wanted to add for completeness. A few more tips for brake fluid flow: 1. When replacing pads, often one must push the brake caliper piston inward. This pushes fluid backward through the system. Some manufacturers do not recommend reverse flow through anti-lock brake mechanisms so the trick is to open the bleeder when pushing a brake caliper piston. 2. When bleeding brakes, always start at the wheel with the longest brake line run from the master brake cylinder and work towards the wheel with the shortest. 3. If you every get air in the master cylinder when it is installed on the car and it has a bleeder, simply run a short drain line from bleeder back up to the reservoir for a short cycle and not-so-messy job.

Hi Raymond, Thanks for your shared opinion and experience, your comments are welcome. I've used the first two methods, the vacuum as well as the pressure method and so far not caused any problems. I agree that at the reverse method there is one big disadvantage issue: the brake system should be flushed prior to reverse bleeding, for the reason as is mentioned in your comment, to not causing some problems pushing some dirt debris in a brake system back into a ABS unit or master cylinder, and so on... ...In that context, the pressure method is the best brake bleeding method for flushing dirty fluid from the system.