Once I bench bleed my master cylinder won't the fluid run out when I disconnect the bleeding lines to hook it up to the lines in the car? How do I prevent this?
They have little plastic plugs that go in there. You might still probably need to bleed the brakes but it will take a lot less time then if you started with the master cyl unbled
yes, a small amount will dribble out , but not the whole MC....just put you finger over the holes , or some small plugs..and install it fast
It's a lot easier to bench bleed the master when it's on the car. Make up a couple short pieces of tubing with fittings on them that curve up and go back into the top reservoir. When you pump it with the pedal, it just goes back into the master. Then just unscrew the bleeder tubes and hook up the brake lines and your done.
They usually come with those little fittings and tubes,but it's pretty hard to see the bubbles quit from the drivers seat.LOL Just leave the tubes and fittings in and put it on the car after bleeding and then remove one at a time and install the lines one at a time.
Some cars don't depress the cylinder all the way, which means if you don't bleed it by hand on the bench there will be a little bit of air that you won't be able to get out once it's on the car. (Unless you pressure-bleed the system, which works fantastic and which I recommend.)
Also - some M/C are mounted on an angle uphill - which will trap air in the 'top' and won't be able to bleed out. Just check the angle of the bore and if it's level then you're good to do it on the car - if not bench bleed it.
Also just to tag onto this topic. Will I need any type of return spring with the Wilwood dual MC set up and swing pedal? Thanks again
Ditto. And leave the MC half full after bench bleeding because you'll be installing it in this manner with no lid on it most likely.
Pressure bleeding is when you make or buy a cap for the master cylinder that has an air hose attachment in it. You fill the master cylinder to the top, put the cap on, hook up an air hose running maybe 10-20 pounds of pressure, and then just crack open the wheel cylinders one at a time until each one runs clear fluid (no air bubbles or sputtering). I use a 1/4 inch thick piece of steel with rubber glued to one side. I drilled and tapped a hole for the male air hose connector, and I just use c-clamps to hold it on the master cylinder. It would be much neater to use a spare lid. The seal doesn't have to be perfect, just good enough to get the pressure to go through the system rather than out the sides of the cap. WARNING: Drop the air pressure back down to zero BEFORE you disconnect the air hose, or you'll get a little geyser of fluid in your engine compartment!! The advantage of this is that it's quick, one person can do it alone, and it makes your brakes as firm as they can be (because it gets out ALL of the air in the lines). The disadvantage is that the fluid comes out faster than you expect it to and can make quite a mess if you're not careful. And if you let out too much fluid the master cylinder will go dry and you'll actually be pumping air INTO the system. I personally stop and refill the master cylinder after doing two wheels.
Fot the bench bleeding, you can make up GOOD hardware with a cheap stop at NAPA--buy and 18" or so piece of pre-fitted brakeline, and get the counter guy to get out the little box of adaptors to fit the line to your ports. Cut brakeline in haly, bendittofit so ends of tube are submerged in reservoir.
A pressure bleeder allows one person to bleed brake systems. I have a pressure bleeder tank made by K-D tools that holds brake fluid under air pressure. I found this link that shows how to make a home made one using a garden sprayer. It looks easy to fab and practical to use. And to answer your question no you don't need to bench bleed the master cylinder when using a pressure bleeder. http://www.bmw-m.net/TechProc/bleeder.htm
The Jalopy Journal
