Use the Proper Brake Fluid

Improper brake fluid will ruin seals in the brake system. Use only standard aircraft
Mil-H-5606 red hydraulic fluid. Never use automotive brake fluid!

Bleed the Brakes

The best method to fill and bleed aircraft brakes is from the bottom up:

  1. Loosely connect a 1/8″ ID clear hose to the brake caliper bleeder screw from your brake fluid source (an oil can works well).
  2. Pump the oil can until the hose is full of fluid with no air bubbles.
  3. Tightly secure the hose to the bleeder valve (open a quarter turn), then pump fluid until the brake cylinder reservoir fills.
    (Leave the reservoir filler/vent cap open.)
  4. Tighten the bleeder valve screw, remove the hose, and reseal the reservoir.
  5. Verify a “hard pedal.” If you get a soft-pedal, pump the brakes several times.
    If it persists, drain and repeat the process.

Tighten & Safety Wire the Brake Calipers

Torque the brake caliper bolts to 90 inch-pounds, then safety-wire per standard aviation practice.

Seat the Brake Pads

New non-asbestos organic brake pads require a thin glazed layer on the friction surface for maximum performance.
Create this layer by:

  1. “Drag” the brakes while taxiing at slow speed with moderate power (do not use maximum braking pressure).
  2. Allow the brakes to cool for 5–10 minutes.
  3. Test at full static run-up. If the brakes hold, break-in is complete; otherwise, repeat steps 1–2.

Hydraulic Fluids

Always refer to your aircraft manufacturer’s maintenance instructions for the proper hydraulic fluid.
Grove brake systems use Buna-N (Nitrile) O-Ring seals compatible with MIL-H-5606, the long-standing
industry standard (–65 °F to 274 °F).

Due to MIL-H-5606’s flammability, phosphate-ester fluids emerged in commercial aviation (not compatible with MIL-H-5606).
The military developed the more fire-resistant synthetic hydrocarbon fluid MIL-PRF-83282, later improved by
MIL-PRF-87257 to address low-temperature viscosity.

Bottom Line: MIL-H-5606 has been replaced by MIL-PRF-83282 and MIL-PRF-87257. All three fluids
are fully compatible and miscible—mix as needed without ill effects.

When switching from MIL-H-5606 you can either:
1. Drain and refill with MIL-PRF-83282 or MIL-PRF-87257, or
2. Top off the reservoir with MIL-PRF-83282 or MIL-PRF-87257 as needed.
Both methods have proven successful with no reported issues.

Other Articles