How to test all new brake lines and flares with no master cylinder installed

[ray_mcavoy]

Even though shop air pressure is considerably lower than the brake's normal operating pressure, it does make an excellent way to test newly installed brake lines to see if the flared connections are making a good seal.

I've done it several times and would rather locate a leak using air instead of having brake fluid weeping out of a connection and dripping onto a freshly painted frame/chassis.

I just pressurize the empty brake lines/system by connecting shop air to the line(s) that would normally connect to the master cylinder. Then I spray all of the connection points with soapy water and watch for bubbles. It doesn't take much to cause a leak with flared fittings where the seal is made by the metal-to-metal contact between the flared end of the line and the seat. It's often just a matter of tightening the nut a little more to stop the leak. And it's real easy to see that it's tight enough when the soapy water stops bubbling.