5 ways to bleed your brakes
Releasing the air trapped in your car’s hydraulic brake system is crucial. Brake systems rely on a master cylinder to push fluid through the lines, and the fluid then imparts force on the piston (or pistons) in an individual wheel’s brake cylinders or calipers. The piston squeezes the brake drum or rotor, using friction to turn speed into heat and bringing the vehicle to a halt. The fluid is very efficient at activating the cylinder/caliper because it is nearly incompressible.
On the other hand, air is compressible; when it’s trapped in your brake lines, air can result in a spongy pedal and an ineffective stopping system. (Modern braking systems also use an electronically controlled distribution block for antilock- and traction-control systems, and the blocks are sensitive to air and to degraded fluid.)
So we agree that you want to keep air out of the system, but on the off chance that a few bubbles sneak in during a project, how remove you do them from the vehicle’s brake lines? There are multiple ways to bleed a brake system, and understanding each method is important so that you can decide the best approach for your project.
Gravity
Let’s start with the easiest of all the options: Doing nothing. Well, almost nothing. The concept here is simple. By filling the master cylinder and opening the bleeder screws at each wheel, gravity will gradually force the fluid through the lines and push out the air bubbles.
This method requires the appropriate tools to catch the fluid as it drips out of the bleeders. In addition, you must ensure the reservoir for the master cylinder never runs dry. Letting it run dry reintroduces air into the system, and you’ll have to drain all the fluid and start from scratch.
What sounds like the simplest method is actually one that’s very situationally dependent. Simple brake systems like those found on early hydraulic-brake-equipped cars can possibly be finished after a gravity bleed, but more often than not, the gravity approach is just the first step of bleeding a system. One of the following processes is usually needed to finish the job.
Pump and pass
Rather than leave the dirty work to gravity alone, sometimes it’s best to make the system work for you. That means using brake pressure to push fluid through the lines. You’ve likely performed this method before: Use a friend to pump the brake pedal three to four times to build up pressure, and then tell them to hold their foot on the pedal while you open the bleeder screw at one wheel. This allows the system to burp fluid—and, hopefully, air bubbles. Close the bleeder before your helper releases the brake pedal and repeat the process until no more air bubbles exit when the bleeder screw is opened.
There are a couple of things that make this pumping method more effective than gravity bleeding. For one, the fluid moves faster, making it more likely to force out any trapped air. Then there’s the fact that building pressure in the system shrinks the air bubbles—because the air compresses—so it condenses large bubbles and speeds their evacuation.
The pump-and-pass method can help when your brake lines have multiple unions, bends, or valves. Each of those tends to allow air pockets to hang around, causing frustration if you stick with just gravity bleeding.
Check valve
The pump-and-pass method is the most popular, but it can be tiring or annoying for the person helping inside the vehicle. Luckily there is a way to eliminate the need for a helper, and it doesn’t require fancy tools.
The first option is Speed Bleeders. These replace the bleeder screw at each wheel with one equipped with a small check ball and spring, making the screw a one-way valve when the check ball is loosened. Connect a hose to the bleeder, open the screw, pump the pedal until no more air is being pushed out, then tighten the bleeder and move to the next wheel. The method is pretty simple, but it does require changing out the bleeder screws.
If you want to accomplish the same task without buying bleeder screws, use a simple bottle and a hose. An empty brake-fluid bottle is often best, but you can create these devices with any number of containers.
Start by pouring a small amount of clean brake fluid into the bottle, then insert a hose, making sure the end will stay submerged in the clean fluid. Then connect the loose end of the hose to the bleeder screw. Open the bleeder screw and pump the pedal slowly to push the fluid and those pesky air bubbles through the system. The bottle will slowly fill as the fluid is pushed out, and since the end of the hose is submerged, it will prevent any air from being pulled back into the brake system.
To make the process even easier, add a zip tie or piece of string to hold your new bleeding apparatus above the brake caliper or wheel cylinder, an orientation which encourages the trapped air to rise up the hose. Cut a hole in the upper part of the bottle so that air you’ve expelled from the system can also escape the bottle and not cause unwanted pressure inside that as well.
Pressure
Sure, the options above are various ways to apply pressure, but they all use the brake system to create the fluid’s push. Another method uses an external tool to place pressure on the brake master cylinder without someone operating the pedal.
The system of tools pictured above creates a steady pressure that keeps air bubbles moving, preventing them from getting stuck in little pockets like proportioning valves or distribution blocks.
Using one of these makes the bleeding process easier, but it also requires extra care when setting up and when topping off the fluid during the bleeding process. Since the master-cylinder reservoir is under pressure while this system is in use, there’s a risk that the outer gasket of the tool leaks while you’re forcing pressure through the brake lines or when you take the tool off to top up the reservoir. Since most brake fluids easily strip paint, don’t take this risk lightly.
Vacuum
Maybe those methods are too pressurizing for you. Luckily, this option is the opposite. We are talking about negative pressure—vacuum, to be precise.
Rather than using the master cylinder to push fluid through, this vacuum tool pulls fluid through the system from the bleeder screw. Vacuum tools make quick work of bleeding a brake system that is dry, or one in which many parts have been replaced (in such a situation, you’ll need to draw fluid over a larger distance).
Products like the MityVac use a hand pump to create the vacuum, but other options are connected to a compressed-air source to pull a vacuum without the need for manual labor.
These tools can be a decent investment if you are bleeding brakes regularly, but if you’re only doing this once or twice a year, the extra effort needed for the other tool-less methods might be worth the savings.
No matter how you decide to bleed your brakes, use the proper fluid and follow the process to ensure you have safe and predictable stoppers. Have a tip? Leave a comment below.
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Motion Pro makes a one way bleeder valve that I use when bleeding my motorcycles’ brakes. I attach it to the bleeder nipple with a very short piece of clear tubing. Once the old brake fluid has passed through the valve, I can just pump away on the brake lever to flush the system with new air-free brake fluid. Works like a speed bleeder but can be moved from wheel to wheel. Might be a good solution for those car owners in winter climates that have had trouble with speed bleeders corroding but like their function.
I can’t believe anyone would bleed from the wheel cylinder to the master cylinder. There are way too many places for air to get trapped since air will not go down, in a fluid,
to push air out the feeding tube attached to the wheel cylinder which is ALWAYS LOWER than the bleeder. Sometimes front brake calipers get mounted on the wrong sides by mistake. You are wasting your time trying to get air out of those calipers with the bleeder screws lower than the feed lines. I read a lot here about bleeding “the farthest wheel first” concept. Since in the U.S. we have had dual safety brake systems that are separate from front to rear, for many decades, bleeding the closest or farthest away bleeder first is irrelevant and in the real world doesn’t really make much difference on the pre-dual systems. The ONLY system I reverse bleed is hydraulic clutch systems. The bleeder screw tends to be at the same level as the feed tube and will not trap air. Occasionally gravity bleeding a clutch is effective and quick enough. I do not bench bleed master cylinders as you should be test fitting the master cylinder first to make sure it fits, that way you don’t have a wet cylinder to return to the parts store. Why mount it twice? Put a shut-off valve on your pressure bleeder so you can slowly push fluid through the fittings before you tighten them. Tighten the fittings, shut the valve off and your done. Only occasionally do you need to bleed at the wheels.
I had to replace my entire brake system. I learned that charging the system with shop air and use soap
bubbles to check for leaks. Stainless steel brake lines do no play well with cast iron calipers.
I read all the way to the end, and didn’t see my method: Take a bicycle tube, a good one (a 26″ is a good size) and cut it clean thru about a foot from the air valve. Do the same on the other end, but add about 4″. Then on the longer side, roll it up a few inches and clamp it securely with one of those wide paper clips–about a 2 incher. Then take the open end of the tube and, after filling the master cylinder to well overfill, stretch the bicycle hose over the MC cap opening and maybe put a zip tie around it. Blow up the bicycle tube to about triple it’s normal diameter. You’ll probably have about 3psi now pressurizing the MC. Now bleed each wheel, keeping an eye on the amount of fluid in MC, adding if necessary. You may wish to look at the MC’s cap diameter first before choosing an appropriate bicycle tube…
I am a semi-retired tech who operated a mostly 1 man shop. When trying vacuum methods, or trying check valve methods I had the issue of air being sucked in thru the bleeder threads. My best friend has been a shortened, adjustable-length aluminum shower curtain rod that I would pump the pedal with and prop between the seat and pedal. It would follow the pedal to the floor as I opened,bled,and closed the bleeder.
Also, if used to hold pressure on the pedal over a several hour period (with brake lights disabled) this method will cure almost any air related problem.
When available, I used a real life buddy which was faster.
Pump and Hold method will possibly cause a seal leak in the Master Cylinder, as you will be pressing the plunger further into an area in the master cylinder that hasn’t seen the plunger before and may have corrosion, rough spots etc that will ruin the plunger seal. It does happen. Use a pressure type bleeder, easy, safe one person job. Do not use DOT 5 unless you are confirming it will work without any issue in your vehicle.
Always use the vacuum method, as I needed to bleed brakes before every track event while doing a nut/bolt check. But… and that’s a big but…. make sure you pump up the brakes before you back out of the garage, as you will have no pedal for the first 3 or 4 frantic pumps before you end up in your neighbors yard.
Don’t ask me how I know this.
My comment has been “Your comment is awaiting moderation” since 9:35am this morning! What’s up with that?! Everyone’s moved on by now! Very frustrating! 😖😖
Seems like just about all avenues have been mentioned. Definitely agree with Teflon tape on bleeders whether it’s vacuum bleeding or hose in container. One other trick that sometimes helps is too leave a “brake stick” on the pedal overnight. Seems to let those last few air bubbles “burp”. Take battery cable off so the battery doesn’t drain though.
Andy’s big brother’s (me) influence might be showing thru in his comments.
One more try…After many decades of bleeding-by-helper (annoyed spouse) in the cockpit, I bought a Motive pressure Kit. Absolutely AMAZING product! I can now bleed brakes efficiently, by myself, and quickly. After the same many years using a glass catch jar, I bought a purpose-made Bleeder Bottle (All Star brand), with magnet to attach to brake disc, and nipple for attaching loose end when not in use (no drips!). No more knocking over the glass jar, or having the bleed tube flip out of the jar and splatter brake fluid on my paintwork (I HATE brake fluid!). These items are SO much superior to the old school methods, I just can’t imagine Ever not using them. One last item of convenience: A drop of tracer blue dye every other fluid flush, so I can SEE when the new fluid replaces the old fluid.
Used hand vacuum bleader on 81 vette after replacing entire brake system..
I was surprised to learn bleeding four piston system went extremely easy and fast. Will never pump pedal again. Loaned it to a friend who could not get a hard pedal, he was sold also.
Some years ago, after trying most of the of the methods mentioned here, and using a helper ,which some times did not end well, I devised a ‘helper ‘ method that did not require that helper. Acquire a long stroke gas spring that will be long enough to reach from the steering wheel to the brake pedal when the pedal is floored. This distance is almost the same length on all vehicles, as we’re all about the same height. I welded a rod bent to a small shape to fit to the steering wheel, with the other end on the brake pedal. The gas spring will push the brake pedal to the floor when a bleeder is opened and hold it there. Tighten the loosened bleeder and reach in the vehicle and pull the pedal up against the push of the gas spring and go to another bleeder. The gas spring will floor the pedal again and again hold it there till you tighten the loosened bleeder. The gas spring will last forever using it this way.
Very clever, son!
Also should mention when pump bleeding the brakes do not push the pedal to the floor, do halve pumps till you build up pressure then bleed.
Yes, half pumps. I always do that. No way to edit comments, but I left out the “C” in the description of the upper end of the gas spring that fits the steering wheel. Pulling up on the pedal and letting the gas spring push it down is a quick and easy to pump up pressure. One doesn’t need to let it go all the way to the floor.
I’d bet everyone who has used the buddy bleed way has gotten out of sync with each other and had to start all over again!
My best and most efficient results are with a pressure bleeder.
I learned on my daughters SAAB 9-3 that we need to start with the LF to ensure the bubbles are flushed from the ABS actuator first. It is the high point in the system and bubbles can easily be trapped there.
I also learned after bleeding a gallon or two of fluid through that car that an ABS module can actually go bad. Had to replace it with a good “used” one form my friends stash of SAAB donor cars.
I got a surplus vacuum pump from some industrial packaging equipment years ago. spent a few minutes making a bottle for it and used it ever since. It was especially handy for doing complete fluid changes on my bikes brakes and clutch and any time I replaced a line on a car. Just hook it up ,turn it on and watch for bubbles and keep the master cylinder full. I also used it make changing the filter less messy on my 350 Thm transmission ,just put the line down the dipstick and suck out most of the fluid before dropping the pan