bad MC and testing

[Flathead Fever]

Originally Posted by 1930artdeco

Just curious about bench bleeding. If you fill and bleed the MC on the bench and then install it into the car you have to hook up open lines to it. Those open lines have air in them, isn't that defeating the purpose of the bench bleed?

When you bench bleed you have a little air left at the end of the master cylinder where the line goes. You leave the line loose and have somebody push down on the pedal which forces that last little bit of air out of the master cylinder and then you tighten the line when the fluid starts to come out. From then on fluid will be forced down the lines and any air will be ahead of the fluid and pushed out. An air bubble cannot go anywhere but down and out. Do not rapidly pump the pedal like your see people do. It can bust up a large bubble into a million little ones. Open the bleeder, push down slow and easy, close the bleeder, let the pedal return and repeat until you get a nice stream of fluid. My dad always put a rubber hose over the bleeder into a jar so he didn't make mess. At work we just let it squirt out on the floor. It did a good job of cleaning the concrete when we mopped it up. Remember that it will take paint off of your restored cars so wipe it off immediately and rinse with water.