Hi Stephanie;
Yep, that’s the cause. Air is compressible and brake fluid isn’t.
The brake bleeding procedure on Piper airplanes is described below:
7-66. BRAKE BLEEDING PROCEDURE (GRAVITY).
a. On both main landing gear wheel brake assemblies, attach a clear plastic hose to the brake bleeders
and extend into container partially filled with hydraulic fluid, MIL-PRF-5606H. The ends of this
hose should be submerged in the fluid. Open both bleeders approximately one and one-half to two
turns.
b. Fill the brake reservoir on the fire wall with hydraulic fluid, MIL-PRF-5606H.
c. Disconnect the toe brake cylinders from the pedal connection by removing clevis pin, washer and
cotter pin.
d. Invert toe brake cylinder to aid in releasing trapped air in the top of the cylinder.
e. Check toe brake pedals in the cockpit to ensure pedals are pulled full aft.
f. Pull the hand brake handle, pumping the master cylinder very slowly approximately 25 times until
fluid is observed passing through the clear plastic hoses at the wheel cylinder.
NOTE: Fluid level in the reservoir must be maintained to prevent air from entering in the line.
g. Tighten both wheel bleeders.
h. Pull hand brake until a firm handle is maintained. PIPER SENECA II SERVICE MANUAL
VII – LANDING GEAR AND BRAKE SYSTEM 01/01/09
1L18
7-67. BRAKE BLEEDING PROCEDURE (PRESSURE).
a. Place a small clear plastic hose on the vent tube of the brake reservoir and place a second small
clear plastic hose on the bleeder fitting on one main landing gear. Place the open ends of these tubes
in a suitable container to collect the fluid overflow. Open the bleeder fitting one or two turns.
b. On the other main gear, slide the hose of the pressure unit over the bleeder fitting then open the
fitting one or two turns and pressure fill the brake system with MIL-PRF-5606H fluid.
c. With fluid continually flowing through the brake system, SLOWLY and together actuate the hand
brake and the toe brake pedal of the side being bled, several times, to purge the cylinders of air. On
dual brake installations, both right and left pedals must be actuated.
NOTE: By watching the fluid pass through the plastic hose at the fluid reservoir and the bleeder
fitting on the gear being bled, it can be determined whether any air is left in the system. If
air bubbles are evident, filling of the system shall be continued until all the air is out of the
system and a steady flow of fluid is obtained. Should the brake handle remain spongy, it
may be necessary to disconnect the bottom of the toe brake cylinders (next to the pedal)
and rotating the cylinder horizontally or even above horizontal and by use of the hand
brake alone, purge the air from the system.
d. Close the open bleeder fitting on the gear being bled. Close the open bleeder fitting to which the
pressure hose is attached; then close the pressure unit and remove the hoses from the bleeder
fittings. Check the brakes for proper pedal pressure. Replace the caps over the bleeder fittings.
NOTE: It may be necessary to remove any trapped air in the top of the wheel brake unit by
applying pressure to the system with the brake hand lever and slowly opening the bleeder
and release the hand lever.
e. Repeat this procedure, if necessary, on the other gear.
f. Drain excess fluid from the reservoir to fluid level line with a syringe.
g. Make sure all lines are secure and all fittings are tight. It should be noted that on older master
cylinders where the hole for the bleeder seat is tapered, the bleeder seat/fitting should be torqued at
75 to 90 inch-pounds. On the newer cylinders where there is a straight hole, torque the seat until the
O-ring seals the hole.
Let me know if this solves your spongy brake problem
Steve
