Soft Brake Pedal

[GAHorn]

Why the left brake pedal required “pumping” to build brake pressure:

NOT the Master Cylinder, which was rebuilt thinking it had a defective “Lok-O-Seal”.

NOT the hydraulic lines leaking.

NOT the flexible line to the caliper, which had been replaced because it was old, stiff, and applied a “twist” to the caliper that appeared to move the linings away from the disc between brake applications.

Nor the brake linings themselves which are new.

But THIS…. which moved the linings away from the disc between brake applications…and therefore required multiple applications of pedal-pumping to gain any braking action. (Click on the pic to set the video in-action): https://photos.app.goo.gl/hHQeBDWfusi38aMGA

(This was first noticed while spinning the wheel on the airplane…After discovering that while looking down from above the wheel…”light” could be seen between the linings and the disc. Normally linings remain in-contact with the disc between brake applications…they just aren’t applying pressure until the pedal is applied.)

Both brake discs are being replaced since these old ones are at minimum thickness (0.20”)

[Richgj3]

This is similar with what happens in C2 and C3 corvettes when the trailing arms need rebuilding. Because a car does many more revolutions of the wheel than our planes, this action actually generates bubbles in the brake fluid. The owner suspects his brakes need bleeding and does so. Then has a firm pedal until driving a few miles again. Similar symptoms with the same root cause. Nice catch.

[Bruce Fenstermacher]

Might never have thought about that. Hope I can remember it next "my brakes are soft" complaint.