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whisperer 09-03-2002 05:33 PM

How to bleed brakes - Print It

Once again I feel the need to do another "Basics" tutorial - this time "How to bleed brakes".

This procedure will work great if there are no mechanical problems in your brake system. Bleeding brakes WILL NOT repair mechanical damage!!! For example if your master cylinder or a wheel cylinder is bad you can bleed the brakes all day long and your brakes will still not work, or will not work correctly.

There are several ways to do this job - one involves 2 people, one pumping the brake pedal and the other opening and closing the respective bleeder valve at each wheel. This method is great for Father/Son/Daughter quality time but doesn't actually work very reliably for bleeding the brakes unless you have lots of practice. The reason is that if anybody makes a mistake in the execution of this "dance" it introduces air back into the system and you need to start over. The other problem with this system is that it takes 2 people, sometimes a luxury we don't have.


The first thing is that if you have changed the master cylinder it needs to be bled separately. Buy one of the $3 master cylinder bleeder kits from the auto parts store, or take an old brake line and bend it around so the end goes back into the fluid reservoir on top. You need 2 lines on a dual master cylinder. Fill the cylinder's reservoir and clamp the flange in the vice on your bench. Using a large Philips screwdriver pump the cylinder until all the air is gone from the brake fluid. It helps to stop every few pumps and let the air rise out of the reservoir. You can do this same job with it mounted in the car but it makes a mess and is more complicated if you have power brakes.

The one real "trick" is to build and use a catch bottle at the wheel end of the system. I use a 1 liter plastic pop bottle with a 1/4" hole drilled through the cap. Then you will need about a 2 feet long piece of 1/4" clear surgical rubber tubing. Push the tubing through the hole in the cap and all the way down to the bottom of the bottle. Then fill the bottle about 1/4 of the way up with brake fluid.

You will have a lot better success on a car with power brakes if you start the engine and just let it idle. Some cars will pump just fine without the power assist, others will just never bleed out. Better safe then sorry, start the car. On non power systems it makes no difference, leave it shut off.

Go to the right side rear wheel of the car and open the bleeder valve about 1 turn. Push the end of the tube onto the tapered end of the bleeder valve and make sure the bottle is supported on something solid. Make sure the tube is immersed in the brake fluid in the bottom of the bottle. With the master cylinder full go inside and pump the pedal no more then 5 times and check the master cylinder level again. You want to be careful not to run the reservoir out of fluid or you will have to start over again. Top it off when necessary during this process. Now pump it about 5 more times and check it again. Repeat, repeat repeat. Check the bottle about every 10 pumps for getting too full.

At this point what you want to look for is bubbles/air in the hose going to the bottle. Once you reach the point that you are not getting any more bubbles then there is no more air in that line. Always close the bleeder before you remove the hose, that way no new air has a chance to get into the system.

Then move on to the left rear, the right front, and the left front.

If you follow this procedure you will have done a proper brake bleeding job and will have no air left in the system. I hope this helps save you a lot of hassles.


bbenthin 09-03-2002 06:06 PM

Great stuff...someday you should put together a post with links to all your "tutorials". Or perhaps a tech/how-to section on VMF where these type posts could be housed for easy reference? Bob ... any thoughts on this?

azuero 09-03-2002 06:08 PM

I have always used the two person system but see that I have done the brakes in the wrong sequence. Thanks. I like this one person method.


cam65fb 09-03-2002 06:11 PM

Thanks for the input. Of course you are correct. Since I do track events, I bleed brakes alot. I recently tried something new for solo brake bleeding, the mini vac tool. Seemed to work well though the system had a lot of small bubles that the manual stated was from an improper seal. I know I had a good seal but non the less, it work for me.

johnpro 09-03-2002 06:25 PM

Great post, Hal. Only thing I'd add or comment on is that I prefer to bench blead the master cylinder in the car. If you're careful it doesn't make a mess. If you install a full master cylinder and aren't careful, it makes a bigger mess [IMG]/forums/images/icons/wink.gif[/IMG].

The other thing I've found is that my little "one man bleeder" thingy works great on the '69's brakes (factory disks in front, drums in back). It doesn't work worth hoot on the front brakes of the '65 and '66. Once I get the bleeder kit on it, there's not enough room to get a wrench on the bleeder. I do the '65 and '66 with the old fashioned "2 person dance". Of course my kids have been doing that dance since they were old enough to reach the brake pedal, so that always helps *LOL*.

mlnielsen 09-03-2002 06:52 PM

I tried the MityVac method, but my hand cramped up after the first wheel...<insert joke here>

Instead, I bought a used 120V vacuum pump. I remove the m/cyl cap, top off fluid. Hook up vacuum line to bleeder, the other end to a catch can. Open the bleeder, turn on the pump, and fill the resevoir as it is pumped out. Periodically check the clarity and bubbles of the old fluid. When it's clean and free of bubbles, close the bleeder and shut off the pump. Repeat at eacy wheel in this order, right rear, left rear, right front, left front. This way you guarantee 100% bleeding.

Another way is to pump fluid thru the m/cyl with a converted pesticide pumper. This method is supposed to be the best way to bleed brakes.

70calypsomach 09-03-2002 07:14 PM

Great post... Thought it would be a good time to ask.....
1. I thought bench bleeding was only needed if you are just replacing the M/C and do not want to pump all that air through your already filled lines. On an empty system it is not needed.

2. I know it does (at least on mine) but why would it matter if your engine is running if you have power brakes. You are still depressing the M/C rod just with no assist, right??

3. It seems like one of the most important factor to a nice and stiff pedal is the rear drums being adjusted properly(On a front disk system). How much drag is too much drag?

sergio 09-03-2002 07:52 PM

Thanks for the info. I think a site with a bunch of these how to articles woulld be great...

BillScott 09-03-2002 08:02 PM

timely post - will try it out on my totally new manual brake system on my '68 in couple weeks.

whisperer 09-03-2002 08:58 PM

1. "I thought bench bleeding was only needed if you are just replacing the M/C and do not want to pump all that air through your already filled lines. On an empty system it is not needed." - Yes, bench bleeding is mandatory to not pump fluid through already bled lines. It also is necessary though with a dry system for the same reason that you use a bottle and hose at the wheel cylinders. When the master draws back on empty lines it will suck air back into the master through the line ports and makes it much harder to get the job done. So, you need to bleed the master either on, or off the car.

2. I know it does (at least on mine) but why would it matter if your engine is running if you have power brakes. You are still depressing the M/C rod just with no assist, right?? - Your power brake booster lets the pedal travel about 1/2 way down before you start to move the master cyl rod without the pwr assist. With the brakes all bled out and adjusted this is fine because you don't require the travel to opperate the brakes. When you are bleeding them the travel is neccessary to push fluid through the system. Like I said in the post, sometimes it works fine, sometimes it doesn't. Better safe then sorry.

3. It seems like one of the most important factor to a nice and stiff pedal is the rear drums being adjusted properly(On a front disk system). How much drag is too much drag? - Trick question....*G*. It is important that drum brakes just brush the drums AFTER the car has been driven. The thought behind this is as follows: brake drums expand when warm/hot. You do not want them to be rubbing when in normal use when driving down the hiway, however they need to be adjusted close enough so that they do not have to travel very much when you step on the brakes. I adjust them so they just "shush" when you spin the wheel and then go step hard on the pedal a couple of times and adjust them again. Then go drive the car around and come back and do the adjustment again. Using the brakes will center the shoes and then they can be accurately adjusted. Of course, most cars have self adjusting brakes which work fine for a driver.

whisperer 09-03-2002 09:44 PM

Yup, you are lucky to have "experienced helpers"............... *G*. I useualy break the bleeder loose with a 6 sided wrench and then hang a very small box end wrench on the bleeder. I know, some of these are realy tight space-wise.

whisperer 09-03-2002 09:48 PM

They have power bleeder systems that are great. They recirculate the fluid back to the master and pull the air out in the meantime. I wanted to try to make this do-able for the regular Joe out in the driveway if neccessary, and with minimum extra equipment.

tmendham 09-03-2002 09:59 PM

This thread is too perfect this week. I have Saturday scheduled for a pad replacement for the front discs on my Jeep. I was going to just go to Midas for a bleed out. NOT ANYMORE!!! THANKS!! Now... let's see if I feel gutsy enough to replace the pads in the rear drums!

At some point, you realize, someone is going to compile the tens of thousands of threads in the old and new forums and create the ultimate Mustang Restoration and Service Manual.

GTClown 09-03-2002 11:05 PM

Nice job, Hal. If only I wouldn't have been in such a hurry over the years and tried to outsmart the unswerving truth I woud have saved myself a lot of grief..

CAponyboy 09-04-2002 04:04 AM

I think we should have a weekly tech lesson. ie:brakes, carb rebuild, ingintion setup, suspension, detailing your stang, parts
ratings etc....

just my .02 cents

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