Brake System

[Bob Steward writes] The brake system on the Grumman American singles is listed in the parts manual and sales brochures as having "optional" passenger side brakes. Not many seem to have been built with the "standard" brakes, so I'll only discuss the brake system as if they ALL have brakes on both sides.

The hydraulic brakes use a Mil Spec fluid commonly referred to as "5606". Its a red petroleum based fluid, as opposed to the Glycol based automotive fluids, and the system is not compatible with any other fluid.

The pilot's side master cylinders each have a built in reservoir to contain the surplus fluid needed as the brake pads wear and the wheel cylinder piston moves out to take up the missing pad thickness. The proper fill level is approximately 1/4" below the top of the reservoir, and can be measured with a pipe cleaner. Filling the system before the fluid level drops far enough to suck in air will prevent the loss of directional control on the ground, due to the steering inputs being only rudder and brakes with the castering nose wheel.

In the event of a soft brake pedal, the brake can be bled by pumping clean 5606 fluid into the bottom bleeder valve on the brake cylinder located on the inboard aft side of each main wheel. A 1/4" box end wrench is needed to loosen the bleeder. Note that many people are confused about the direction to turn the bleeder screw, since its upside down.

A pistol grip type oil can with a short section of clear plastic line slipped over the tip is a good way to force fluid into the system. The vinyl line used on aquariums air systems works well, as does some types of surgical rubber tube. Have the oil can filled with several ounces of 5606 and the flex hose installed and pre-filled with fluid before beginning. Take the filler plug out of the master cylinder reservoir on the correct side of the brake system, and then put your 1/4" box end wrench on the bleeder fitting and crack it open. A drop of fluid ought to come out to let you know you have opened the valve enough for the fluid to flow. Leaving the wrench on the bleeder screw hex, slip the end of your flex hose over the end of the bleeder screw and begin pumping. You are probably going to force a small air bubble into the system, so you will need to bleed it enough to purge it from the lines to the master cylinder on the passenger side and then through the lines to the pilot's side master. My hand pump oil can takes 15-20 strokes to accomplish this. Snug the bleeder and leave the hose attached.

Check the pedal on the pilot's side and if firm, then you can stop pumping. If not, open bleeder and repeat until the pedal is firm.

Now check the fluid level with a pipe cleaner. If its not up to within 1/4" of the top of the reservoir, bring your pump inside and fill the reservoir. Re-install filler plug when done.

There are many reasons why the brake pedal might get soft. Not all of them are due to the loss of fluid. A continual history of fluid loss requires that a careful inspection of the brake masters, flex lines in the cockpit, hard lines in the cockpit and especially the aluminum hard line from the wing walk area to the wheel cylinder need to be inspected to find the cause of the fluid loss. Cracks in the flare of the aluminum tube where it enters the caliper are very common, especially on the older members of the fleet. The entire line can be replaced with a new part from FletchAir or one fabricated in the field from 5052 aluminum tube (0.035" wall) or many have been repaired with a 6" section of teflon lined steel braided hose and a straight union AN fitting to couple the re-flared line to the female flex hose.