How to Test Brake Line Fittings

Tools for Testing Brake Line Fittings

Fittings allow steel and flexible brake lines to link to a mechanical device. Steel brake lines are flared at the ends, and these flares are drawn into, and sit precisely within, the fitting. Flexible hoses, like those running from the steel frame lines to the calipers, have similar fittings.

Fittings are considered sound if no fluid is leaking from them. The test to determine their relative soundness is time consuming, but very simple.


You will need a:

  • Good service manual or owner's manual showing the location of the major portion of the base brake system from the master cylinder, to vales, to calipers and wheel cylinders
  • Flashlight
  • Creeper or piece of old carpet
  • Good friend, a long stick or long pry bar
  • Pair of safety glasses

Brake systems work through pressure, so they must be tested under the same conditions they work under, and pumping the system up by pumping and holding the brake pedal down is a good way to simulate a stop.

Once all the major components are located have your friend get in the car and pump the brake pedal several times with the car off, and hold the pedal down on the last pump. If no friend is available, pump the system up yourself and on the last pump push the pedal down and hold it in place with the stick or pry bar, wedged against the front of the driver's seat.

Beginning under the hood, check all the fittings beginning at the master cylinder and working your way down and towards the rear of the car. Calipers have a special fitting called a banjo fitting that seals itself with two copper washers, one on each side. Make sure you check around the copper washers for leakage, and replace them with new ones if needed.

Wear your safety glasses. Brake fluid is corrosive, and your system is now under pressure. Getting a squirt of high-pressure brake fluid in the eye can lead to a trip to the emergency room.

Check all sides of each fitting. Leaks should be readily apparent. Keep your ears opens as well for hissing noises, or the sound of fluid hitting another part of the car, like the frame or body panels. The creeper and carpet will ease any movement under the car so you can reach where the lines and hoses attach to the calipers and wheel cylinders.

Usually pumping the system with the car off is enough to look for most leaks. However, if you still suspect a leak then start the car and pump and hold the brakes adding the brake booster to the pressure potential.