[wslade2]

Oh so familiar that corroded look! I have been living in the zone. Mine were similar (but sorry not that bad).

I have attached a picture below.

I have been working on brakes for months and months. Felt it was so necessary for an event of engine out on take off, launch abort and emergency stop on remaining runway.

First of all how have your brakes been performing? I have noticed a slow sinking and softness of the pedals (just not present on my other airplane) ever since I took possession.

I started with rebuilt swivels as mine were leaking quite badly and the system mostly had air. Next was all new flexible lines. Then rebuilt master cylinders (set that gap right on the lock-o-seal) and rebuilt parking valve.

Still softness.

I changed the o-rings in the calipers and through all this purged/flushed the system what seems a hundred times after all the multiple fixes. Tip: aircraft spruce has a fitting that tightens onto the brake bleeder screw to make back flushing a breeze. They also sell a whole set up but I just got the connector, sold separately, and hooked it up to a $19 garden sprayer with some vinyl tubing; much more cost effective. A tube in the master cylinders routed to catch bottle and flush until bubbles out. Also aircraft spruce sells a bleeder nut that has an o-ring eliminating any chance of air and leakage while flushing the system. I also ended up cracking the lines at the parking valve to get a persistent bubble out that wouldn't flush.

changed rotors and pads (their own story as the cleveland brake manual has errors for our aircraft).

Despite all this, persistent softness and high speed taxi stop tests were disappointing in what would happen with a panic stop.

I'm getting to the point.

Very frustrated with all this work and persistent softness, so went over the system multiple times. As mshac points out check for leakage at the calipers. But here's the twist. I saw none. Until one day I braked hard and right after removed the shoes and pulled the calipers. There I saw a slight ooze from around the pistons that was not enough to to cause a drip outside of the assembled caliper but was not holding full pressure. Gummy residue confirmed oozing that on the hot brakes never led to an easily seen drip.

Closer exam on disassembly after some good cleaning showed what I call micro pitting in the cylinder wall that was letting the brake fluid ooze out past the new o-ring. (see attached photo). An unexpected corrosion induced complication. Tried smoothing the wall with 2000 grit till the pits were gone but appears this lead to larger bore, thousands of an inch oval shaped and did not stop the oozing; now oozing by a new issue-out of round and too large.

So, I gave up and headed for a pair of brake assemblies. Voila, lots of calls, very expensive and not available in our supply chain pandemic world.

After some thinking it dawned on me I can reuse all the parts of the original assemblies and just get new caliper cylinders. Discovered the hard way through parts ordering and returning, the cleveland application manual has incorrectness for our aircraft. Be sure to carefully look at their diagrams and make sure their diagram matches what is on your aircraft. I think I have something similar to a seneca setup in the end. Once again, supply chain and stock issues. Aircraft spruce had one cylinder in the their multiple warehouses. Chief Aircraft after a couple weeks was able to get the other cylinder drop shipped from cleveland brakes with notice another production run was a couple months off if anything else needed. At the time felt like I had the only 2 brake caliper cylinders in the world.

This seems to have solved my problem.

So take a close look at the cylinder wall and see of any if that micro pitting is there. Be aware of oozing that may not be outwardly visible. You do not have to get a whole brake assembly (unobtainium) but might be able to just get corroded component (less unobtainium?) at reduced price and reuse everything else. Test your brakes.