BCPs

I need a little help. Hoping someone has come up against a similar situation and can offer some guidance.

So I flew the 180 to Atlanta for Heli-Expo last week and when we landed it felt like the brakes were dragging. By the time we got to the FBO it was hard to taxi, requiring significantly more power than normal.

We headed to the expo but asked Hill Aviation to have someone look at it. A&P called a few hours later and said all was fine and he could not find anything wrong with the system.

We managed to get back to NC but they were still dragging to the point that you can't push the airplane easily on the ramp. Here is what I know:

- Aircraft upgraded to Cleveland 199-62 Wheels and brakes
- New linings install at recent annual. Log book shows the correct (199-10500) P/N but I have no way to verify thats what was installed.
- I disassembled the caliper and it is clean and floating easily
- as soon as I cracked the 4 AN-3s that hold the two caliper halves together the wheel spins freely
- installed brake linings mic at about .238" (ish) thick each
- Parking brake cable is loose when off

The only thing that makes sense to me is that the replacement linings are too thick and dragging. As they heat up they drag more causing even more heat and drag.

Does anyone have a new set of Cleveland 199-10500 or Rapco RA99-105s that they could throw the micrometers on?

Any other thoughts? Ill check the master cylinder fill port vents to make sure they are not plugged but that seems unlikely on both at the same time.

Thanks in advance\

N2732K

I’ve seen them shimmed many times when they do that. My mechanic made them out of scrap sheet aluminum but I think you can also buy them.

Water in the brake fluid maybe? As it heats it expands and causes more pressure...

Shims are a good idea...ill check that out.

Should not be water as the system has not been opened, but 5606 is cheap so maybe a flush is in order for good measure.

Did you disassemble the pistons from the calipers, clean any corrosion from the caliper and replace the O-rings on the pistons?

This happened to me when I replaced the pads once. The issue in my case was a ridge in the wheel cylinder that prevented reliable releases for the new pads. I spent about 2 hours to go to NAPA for a $10 brake cylinder hone, honing and cleaning the cylinder, reassembling, and taking for a high speed taxi test. Never saw the problem after that.

Might not be the issue, and shims would address the same issue in a rough way if that was the issue.

Good point regarding the caliper piston. Ill order the o-rings and have a look inside.

If you have pressure in the brake lines, then the problem is in your master cylinders behind the rudder pedals. Often neglected. The Loc-O-seals need to be replaced. They aren’t allowing the fluid to flow back to the reservoir when you release the toe brakes.

Buy all new seals per your parts manual, and new hoses to connect the master cylinders to the hard lines if they’re more than 10 years old. Install these new parts, and enjoy peace of mind.

There are factory insulator/shims you can get. Not knowing the all there is about your particular set they may have been originally installed and left out over time. They do degrade with time and crumble, so they just get left off. These are some from Spruce, by Rapco:

https://www.aircraftspruce.com/catalog/lgpages/rapcoshiminsulator.php?clickkey=88897

Pinecone wrote:If you have pressure in the brake lines, then the problem is in your master cylinders behind the rudder pedals. Often neglected. The Loc-O-seals need to be replaced. They aren’t allowing the fluid to flow back to the reservoir when you release the toe brakes.
…..

I'm also thinking the loc-o-seals might be the issue.
It's a little washer with an even smaller o-ring inside it.

It’s a fairly inexpensive fix. Even if my diagnosis is wrong, I’d wager that you’ll find a lot of crap in the bottoms of the master cylinder reservoirs, and deteriorated brake hoses that no one ever sees. You’ll be glad you dug into them even if it isn't the final solution.

Based on the report of residual system pressure, I wager it is the final solution.

So with a big trip coming up I decided to heed the good advice and have ordered all of the parts for a brake overhaul. Too cheap not to just go through it. Interestingly, at looks like there was a design change at S/N 1805301 and the later model master cylinder no longer have the "Lock-O-Seal" and only contains 1 o-ring. (as far as I can tell from the IPC).

Ill post what I find when complete. Thanks for the advice and nudge in the right direction..

Regards,

W

I looked up your parts on McFarlane’s site and agree you have selected the correct part numbers.

Thanks Pinecone.

A 2nd set of eyes makes me feel better. Parts arrive tomorrow so hopefully will be back in the air by this weekend!

Brake rebuild step 1 complete...

- Calipers stripped, honed, plastic media blasted, and painted
- Pistons cleaned up and ready for re-install

Parts arriving tomorrow...flying Saturday. (hopefully)

Brakes are working better than ever and we are back in the air. Thanks for the help and comments.

Regards,

W

Was there a smoking gun?

Yes. It turned out to be the calipers, not the master cylinders. Both the pistons and bores were nasty and gummed with brake dust and a little corrosion (only on the caliper). This was causing them to hang up and not retract / relax.

Once cleaned up, the pistons were in great shape and the o-ring surface of the bore was smooth and without ridges. Went back together no problem and no leaks.

The $80.00 pressure bleeder was a good investment and worked perfectly first try. less than 10 minutes to bleed both sides with little mess.

Cwillfly wrote:...The $80.00 pressure bleeder was a good investment and worked perfectly first try.....

I'm low budget, and use a metal pump-type oiler can from Napa along with a short piece of clear plastic tubing.
Works just as well as the aircraft-specific equipment in my experience.

Cwillfly wrote:Both the pistons and bores were nasty and gummed with brake dust and a little corrosion (only on the caliper). This was causing them to hang up and not retract / relax.

Once cleaned up, the pistons were in great shape and the o-ring surface of the bore was smooth and without ridges. Went back together no problem and no leaks.

Bingo. Glad it worked.