Brake Bleeding – Gravity, Manual and Vacuum Bleeding
April 19, 2009 12:11 pm How To Auto Repair
Brake bleeding sequence; right rear, left rear, right front and then left front
Brake bleeding is necessary when a system has been opened or the brake fluid has been allowed to get too low in the master cylinder. Air can enter due to a low master cylinder caused from a leaky wheel cylinder or other brake component. If a hydraulic part like a wheel cylinder, caliper or brake line has been replaced the system will need to be bled. Brake bleeding at the wheels can be done several different ways. The most common way is old fashioned manual brake bleeding.
It’s when an assistant pumps the brake pedal up and holds pressure while the bleeder screws are opened at the wheels letting air escape. When the fluid streams out without any air and the pedal is firm the job is done.
Manual Brake Bleeding
Manual brake bleeding as stated above involves two people working together. The master cylinder must be kept full during the entire process or air may re-enter the system. While the assistant applies pressure to the brake pedal, start with the wheel that is farthest away from the master cylinder. Open the the bleeder screw allowing fluid and air to stream out. The assistant must keep the pedal down until the bleeder screw is closed. Then the process is repeated several times at each wheel until all the air has been bled out, be sure to keep the fluid level up in the master cylinder during this process.
But, did you know that this job can be done by ONE person reducing the time and trouble involved? Gravity or Vacuum bleeding makes this possible, read on for more info.
Gravity Bleeding
Gravity bleeding can be done by ONE person. The fluid in the master cylinder is naturally at a higher point than the bleeder screws at the wheels. So gravity will pull the fluid slowly down when the bleeder screws are opened. The process can be sped up a little by lightly pumping the brake pedal while when the bleeder screws are opened (avoid pushing the pedal all the way to the floor). All bleeder screws at the wheels can be opened at once. Like manual brake bleeding, the brake fluid in the master cylinder needs to be kept from going empty or air will enter the system. The bleeder screw farthest wheel from the master cylinder should be closed first.
Vacuum Bleeding
Vacuum bleeding is done in the same sequence as manual brake bleeding. The advantages of using a vacuum brake bleeder like a Vacula brake bleeder is that it saves time and is done with less mess. Vacuum brake bleeders (not the hand pump type) use shop air to create a venturi vacuum that allows the fluid to be drawn out through the bleeder screws quickly. The tube from the vacuum brake bleeder is attached to the bleeder screw and the screw is then opened. The clear tube makes it easy to see when straight fluid with no air is being drawn out.
Hydraulic Clutch Bleeding
One of the hardest hydraulic systems to bleed can be clutch master and slave cylinders. Many times manual bleeding or gravity bleeding cannot remove the air from these systems. On more than one occasion during my time as a technician, my vacuum brake bleeder has saved the day by pulling the air out of a hydraulic clutch system. It seems like the Ford Ranger and some foreign cars can have air trapped in their clutch system easily. When this happens it’s a great feeling to have a vacuum bleeder on hand that can easily remove the air from a stubborn system.
Question: How do I bleed my master cylinder?
Answer: Bench bleeding a master cylinder is required before installing it on the car, see our master cylinder bleeding article for much more information.
Question: I’ve replaced all the brake lines on my Chevy truck, no matter how much I bleed the system the pedal sinks to the floor. What could be the problem?
Answer: It could be a bad master cylinder. But the master cylinder could just have too much air (lost it’s prime) If the brake fluid went completely empty, the master cylinder may need to be removed and bench bled, then put back on and bled at the lines and then at the wheels.
Question: After putting on new wheel cylinders, I’ve gotten all the air out of the system, but the brake pedal seems a little low. Any suggestions?
Answer: Brake pedals in different cars have different characteristics, simply put they can feel different compared to other make and models, but it could be normal for that car. If you are sure that the pedal was higher at one point ten the rear brakes may need to be adjusted to bring the pedal up (avoid over-adjusting).
Question: I just replaced the front calipers on my Explorer. Do I need to start with the rear brakes when I bleed them?
Answer:You should only have to bleed the front brakes since you only opened the system in the front. Hopefully you didn’t let the fluid go empty in the master cylinder while changing the calipers or it will be harder to bleed. Also you may want to bleed the rear too, not because of air but to replace the fluid for regular maintenance.
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Steve L. :
Date: May 13, 2009 @ 2:42 pm
Don’t forget about pressure bleeding! I use the Motive Power Bleeder and it works great. A true one person bleeder and very affordable also. Just my .02….
Steve L.
Ed D :
Date: August 22, 2009 @ 11:12 pm
Why can’t the master cyl. be bled on the car?
dennisb - Auto Tool Sales :
Date: August 23, 2009 @ 9:11 am
Ed, good question. There are a couple of reasons that come to mind why bleeding a master cylinder off the car works better in most cases.
1. Since air rises to the highest point, it’s important to have the master cyl mounted level – in a bench vise, that’s easier to control. On the vehicle mounted on a brake booster, sometimes they are on an angle.
2. When a m/c in placed in a vise, one person can easily push the plunger with a screwdriver and monitor the bubbles going through the bleeding tubes. Or if no bleeding tubes are used, it’s easy to hold fingers over the ports.
Theoretically, if the master cylinder is level, and the lines are removed, it could be bled on the vehicle.
Keep in mind that even after the master cylinder has been bench bled, installed on the vehicle, it will need the brake lines cracked and bled on the vehicle (with an assistant) to remove the last bit of air.
Al Sautner :
Date: December 28, 2009 @ 12:45 pm
I have a 65 corvette. No power brakes. I put on new wheel Cylinders on all wheels and brand new Master Cylinder. I bench bled the Master and put it in the car. I did a complete bleeding of all wheels starting with the furthest….Now I get a good hard peddle as long as I pump it 5 or more times. If I hold it the pressure stays good and hard. If I let the brake alone for one minute the peddle go’s right to the floor…What can I do….? The repeated the process four times and went through 3 quarts of Dot 3…Help me…!
dennisb - Auto Tool Sales :
Date: December 28, 2009 @ 1:34 pm
Al, it sounds like you’ve bled the system thoroughly, although it is common when there is air in the system that the peddle can be pumped up temporarily.
Other Things to Try
1. Make sure there’s no tiny leaks from anywhere making the pedal sink. Clean brake fluid with brake-clean and dry the backing plates so that a small trickle may be easier to detect.
2. Also, If the vehicle has drum brakes make sure the shoes are adjusted properly. Sometimes machining the brake drums is needed to be able get the best adjustment.
Al Sautner :
Date: December 29, 2009 @ 8:49 am
Thanks Dennisb…..This car has all disc brakes on all 4’s. I never had so much trouble bleeding brakes…! I agree with you on the air in the system. I am going to buy a Vacuum bleeder this weekend and try it again. I put the best O ring type breaks on and there is no leaks anyplace….I hope I get this running very soon. It will be winter soon and I will not get a chance to ride it….!
Al Sautner :
Date: December 29, 2009 @ 9:22 am
Thanks Dennis….I live in South Carolina….Lots of nice weather even in December. It is winter today….39 degees. My vette does not see rain or Cold. It sits in a heated garage and with a cover on it. Thanks for all your help and advice. Where do you live…? By the looks of the picture…California..?
dennisb - Auto Tool Sales :
Date: December 29, 2009 @ 10:00 am
Al, I’m in Riverview, Florida just outside Tampa.
dennisb - Auto Tool Sales :
Date: December 29, 2009 @ 9:05 am
Al, if the parking brake in incorporated into the rear calipers, I would check to to make the pistons are not retracting.
The vacuum brake bleeder is a good idea. If you get a fluid evacuator that has multiple purposes, you will find other uses that you may not even think of right now.
Al, you may want flip the page on the calendar – December 29th qualifies for winter. 🙂
dave :
Date: March 20, 2010 @ 11:07 am
I blew a rear line on my 94 Jimmy. I have replaced the lines from the Master back to the rear wheels. After several tries at bleeding the lines manually, I took the cover off of the Master Cylinder and pressed down the break pedal. The fluid shot out of the open resivoir from the first port. Is this normal, or is there something wrong with the Master Cylinder?
Pierre :
Date: December 26, 2011 @ 10:35 pm
brakes go to floor like the vaccum buster is not working? can someone tell me if it has a vaccum buster or if not a master cylinder?