chronically dragging brakes

[GeorgeC]

They ended up not replacing the flex hoses, but I should have insisted. After my second landing today, it felt like it was pulling a bit and needed more rpm to taxi than it should have.

 

[Tom-D]

check to see that the hose is routed properly.

 

[GeorgeC]

There was some corrosion on the left caliper piston which was causing it to get hung up. I think I will add that to the list of things to check at annual whether it needs it or not.

The internal flex hoses were the originals from 1950. For completeness, I had them replaced, along with the external flex hoses.

 

[Dan Thomas]

The internal flex hoses were the originals from 1950. For completeness, I had them replaced, along with the external flex hoses.

They sure didn't owe you anything. I've replaced hoses from the late '50s and they were as hard as wood and the steel braid was corroded. Bending them usually resulted in breaking them.

 

[GeorgeC]

Typically when brakes drag either the caliper is due for replacement or there is corrosion on the hardware.

Next question, do the calipers have a practical calendar life?

 

[Dan Thomas]

Next question, do the calipers have a practical calendar life?

Depends on the environment. They're aluminum, and they're not sealed up like auto calipers, so they corrode when moisture and dirt and airborne pollutants get into them. Corrosion causes leakage and sticking. The O-rings take a set, since they're Buna N (neoprene), a material dating from WW2, and auto calipers use more modern seals made of more modern materials. Hangaring the airplane helps reduce the corrosion issue, but the O-rings still suffer.

The calipers I've replaced were either corroded and pitted and couldn't seal, or the bores were scored and didn't seal. Sand can get in there and the piston starts grinding it against the bore and cutting grooves that let the oil start seeping out. The oil attracts more dirt, making the problem worse.

 

[Magman]

I’ve seen tubing or so-called “flex-hoses” that weren’t .

This can load the caliper against the disc.

The Torque Plate that carries the load can distort and

lead to rubbing.

When Looking at the mating surface of caliper it should parallel disc .

Occasionally, the pad wears the disc and leaves a ridge at the edge.

This can give a rubbing , chatter or poor braking .

Might be more prevalent on McCauley.

 

[Ron Stowell]

Look at the o rings on the brake pucks themselves. The most common is MS28775-222, about .75 cents a piece and you will need 4 each. We have found that over time they become hard and do not move as freely as when first installed.

 

[GeorgeC]

After a couple of trouble-free years, the right brake dragged a bit yesterday. Once more unto the breach...

 

[GeorgeC]

I pulled them apart yesterday and the guide pins were nasty. They cleaned up easily with scotchbrite and antiseize. Lesson learned: don't assume they were cleaned at annual.

An A&P friend also suggested that my flex lines were bulging because they were too long, which sideloads the guide pins and makes them more likely to get hung up.

 

[Doug Reid]

You did good. Always check simple things first..pads need to float on guide pins. Also, verify that brake cylinders are releasing pressure. You should be able to see slight movement of brake pads when applying brake pressure, and a slight movement when released. I helped a friend push his Cub into a hangar a few years ago and the right brake was dragging so bad that we could barely push it into the hangar.

 

[Magman]

I never tell owners to “Fill the brake fluid”.

It’s “ Add more 5606”.

Encountered one guy that put auto fluid in reservoirs on a Vagabond.

One of the lightest aircraft made was very hard to push.

Ultimately both expander tube brake assy. had to be replaced.

 

[Dan Thomas]

I pulled them apart yesterday and the guide pins were nasty. They cleaned up easily with scotchbrite and antiseize.

The antiseize will attract dust and make a sticky sludge and it will seize again. One needs to use a dry silicone spray lube, or dry graphite.

Annuals don't typically include taking the calipers apart and cleaning stuff. That's an IRAN item. The short hoses will indeed cause some binding. Sometimes you can fix that by rotating the hose elbows a bit.

 

[Dan Thomas]

I never tell owners to “Fill the brake fluid”.

It’s “ Add more 5606”.

Encountered one guy that put auto fluid in reservoirs on a Vagabond.

One of the lightest aircraft made was very hard to push.

Ultimately both expander tube brake assy. had to be replaced.

Yup. The wrong fluid destroys the rubber stuff. For 12 years I was a foreman in a large brake rebuilding shop, mostly air stuff but some vacuum and some hydraulic. One of the biggest causes of failure in the hydraulics was using engine oil in the brake system. The seals in those are close to natural rubber, and the DOT3 fluid is a vegetable-based fluid, compatible with the seals. In the airplane, the seals are synthetics and the DOT3 fluids, containing alcohols, attack them. That DOT3 stuff will lift the paint off your car, too.

 

[GeorgeC]

The short hoses will indeed cause some binding. Sometimes you can fix that by rotating the hose elbows a bit.

That sounds worth trying. It's like there's a foot of hose that only has to go 11 inches, and it makes a bulge in the middle like in the picture above.

The antiseize will attract dust and make a sticky sludge and it will seize again. One needs to use a dry silicone spray lube, or dry graphite.

Funny. An A&P friend said to use oil. That sounded like a terrible idea to me.
A fellow tailwheel pilot uses grease. That also sounded like a terrible idea to me.
An A&P/IA friend said to use antiseize. I figured I'd give it a try. It smelled pretty volatile so I figured that whatever solvent/carrier would eventually evaporate, but maybe not. I'll have to re-do them soon enough, and I need more practice safety wiring anyway.

Ida thunk silicone or graphite wouldn't hold up to the temperatures involved, but I'm willing to be wrong.

I'd previously purchased a can of dry moly spray lube, maybe I'll give that a try next time.

 

[Bell206]

I'd previously purchased a can of dry moly spray lube, maybe I'll give that a try next time.

FYI: As I recall for years Cleveland didn't call for any lube on the anchor bolts. Keep them clean and everything worked well. However, at some point they went with a dry lube recommendation which I believe is called out in the Cleveland CMM if you want specifics. I've only used a dry lube or nothing at all.

 

[GeorgeC]

FYI: As I recall for years Cleveland didn't call for any lube on the anchor bolts. Keep them clean and everything worked well. However, at some point they went with a dry lube recommendation which I believe is called out in the Cleveland CMM if you want specifics. I've only used a dry lube or nothing at all.

Son of a gun...

Anchor Bolts / Torque Plate Bushings
...
Non-Amphibious environment:
* Silicone Spray
* Dri-Slide Multi-Purpose Lubricant
* LPS Force 842 Dry Moly Lubricant

GeorgeC,
TYFTMTRTFM

 

[GeorgeC]

I'd only painted on a thin layer of antiseize with a qtip, but after a month, it indeed felt like a sticky sludge. I wiped it off and went with dry moly.

Next question: it occurred to me that nothing prevents rainwater from wicking into the gap between the piston and its bore, which I'm sure creates an environment conducive to corrosion. If I can get an A&P's help to pop the piston out and clean things up, can anything be done to prevent future corrosion? I'd think a thin film of something (silicone grease?) would help keep water out.

 

[flyingron]

Left side was vented, right side was not.
.

My Navion uses Cessna rudder pedals on the pilot side to work the toe brake STC. I've broken a couple of them over the years. The good news is that the master cyls only connect to one tang, so you can flop them left for right in a pinch.

 

[Magman]

My belief is that any treatment you mentioned WILL come in contact with the

o-ring. If not compatible the seal will swell and the brake will drag.

It seems that corrosion issues are much more prevalent in low usage

aircraft.

Low fly time = High corrosion time

 

[Bell206]

I'd think a thin film of something (silicone grease?)

I wouldn't do that. The only grease recommended in the piston bore is o-ring grease. Keep in mind added grease holds dirt and debris just like your anti-seize did. From a corrosion standpoint, I had good success by keeping the whole area clean especially if you operate in grass or other similar areas. For example, disassembling the caliper at every annual and clean things ups will go a long way in keeping corrosion at bay. I wouldn't sweat rainwater so much but if you think its a problem you could also make some wheel covers, etc. Regardless, corrosion needs an anode, cathode, and electrolyte to form so by simply keeping things clean you usually prevent all 3 from setting up shop. Just don't use a pressure washer.

 

[Magman]

There are MANY aircraft that have calipers that are 50+ years old.

Even some of the dreaded “ 3 piece McCauley’s “ are still in existence!

 

[Dan Thomas]

Any grease on the caliper piston will attract grit that will score the bore. I've seen that too often.

On the pins, a dry lube is best, as Cleveland mentioned. If you're concerned about heat, you can get a dry spray-on teflon lube. Bendix specified it for the rubber contact nipples for the ignition harness in their magnetos.

 

[Racerx]

Anti-seize is great... depending on the application.

On our ironworker, the guards have acme thread. I lost an argument with my dad. He insisted on anti-seize. Within a month they were so gummed up you could hardly move them. I eventually won the argument.

 

[geezer]

There may be a better solution to the rusting pin problem
The 'blue' on firearms is a phosphate process that makes the steel rust resistant, and harder.

Go to a gun store and buy a bottle of the bluing chemical, and follow the directions explicitly, as there are several chemicals that can do the process. There are both liquid and paste versions, I prefer liquid

4 applications using a qtip and re polishing and cleaning produces a good thickness of 'blue'.

Follow with a light oil, rubbed in thoroughly, to fill any pits in the surface, then with a clean cloth and friction only, no solvents, remove the oil as completely as you can. The trace of oil remaining will not hold much dirt. Dry lube to your preference.

If convenient, the inside of the holes in the plates may be done too. Skip the steel wool polishing of the hole!

I have done this to a lot of steel tools, and the results are very satisfying.

 

[Dan Thomas]

There may be a better solution to the rusting pin problem
The 'blue' on firearms is a phosphate process that makes the steel rust resistant, and harder.

Go to a gun store and buy a bottle of the bluing chemical, and follow the directions explicitly, as there are several chemicals that can do the process. There are both liquid and paste versions, I prefer liquid

4 applications using a qtip and re polishing and cleaning produces a good thickness of 'blue'.

Follow with a light oil, rubbed in thoroughly, to fill any pits in the surface, then with a clean cloth and friction only, no solvents, remove the oil as completely as you can. The trace of oil remaining will not hold much dirt. Dry lube to your preference.

If convenient, the inside of the holes in the plates may be done too. Skip the steel wool polishing of the hole!

I have done this to a lot of steel tools, and the results are very satisfying.

If it isn't approved by the manufacturer of the brakes, don't do it. Hardening steel makes it more brittle and more likely to break. Many paint strippers are famous for hydrogen embrittlement of steel parts and are not approved for use on steel aircraft parts. Imagine stripping the paint off a set of Cessna gear legs and then later having one of them snap on landing.

https://en.wikipedia.org/wiki/Hydrogen_embrittlement

Hydrogen peroxide is commonly used in the bluing process, and it's also part of the environmentally-friendly paint strippers. Phosphoric acid is used to remove rust before bluing, and it has hydrogen in it, like most acids.

 

[GeorgeC]

An A&P friend also suggested that my flex lines were bulging because they were too long, which sideloads the guide pins and makes them more likely to get hung up.

I had shorter ones installed, they bulge less:

I'd only painted on a thin layer of antiseize with a qtip, but after a month, it indeed felt like a sticky sludge. I wiped it off and went with dry moly.

Dry moly doesn't seem to do much in terms of preventing corrosion. Rather than painting on a layer antiseize, I blotted some onto a paper towel and rubbed it into the surface of the metal, leaving it looking matte and dry. We'll see how that goes.