Brake Fluid

[JW Scud]

The Colonel seems to know a lot. Is this statement true about the hydraulic fluid?

"Brake caliper pistons apply hydraulic pressure when you push the pedals but there’s no retraction mechanism when you let off the pedals. The tolerance between brake pads and rotors is very small. As brake pads wear we add fluid to the system so that tolerance remains constant."

Thanks

[Colonel]

Funny you mention that. On the weekend, Eric says, "I have no right brake".

Out comes the armrest. I have a thumb pump from Home Depot with 41 in
it. I pop the filler cap, and sure enough, it's down. I top it up, and Eric says
it's better than the left one now.

A thumb pump with 41 is an essential part of any hangar. I used to top up
brakes in just about everything with it.

I might suggest that before you just top it up, that you take a flashlight
and peek at the pads. Make sure there is some meat remaining on them,
and that they are dry. You need to stock some of those O-rings that go
on the puck, because over the years, they square off and start to leak.

While you're ordering O-rings, get some for the 1/8th fuel drains. I am as
guilty as everyone else of changing them, when all you need to is replace
the tiny o-ring on the tip, which gets distorted over time.

Also, be sure and stock some pads and rivets, and a riveting tool. They
don't cost much, and with a 1/8 inch drill bit, allow you to change brake
pads on light aircraft.

Don't over-squeeze the rivets - it cracks the heads, ok?

Final note: never, ever mix brake fluids. Light aircraft use mineral oil
aka Aeroshell 41 which has a conveniently low flash point and will catch
fire if you look sideways at it.

Cars use DOT3/4 or DOT 5 (rare). Do NOT mix them.

[Scudrunner]

Neat little feature I recall from flying the Islander was the little brake reservoir on the back side of the rudder pedals.
We had a slow leak on the one side so before we could get her in the shop every few landings I would pop the top and filler up and keep going.

I really appreciated that part of British Engineering not much else but that was nice.

[JW Scud]

So it looks like having to add a bit of brake fluid to a non-leaking brake, is a sign of normal brake wear.

[Colonel]

Oh yeah. It brings the pedal back up again.

Try to do it, before it gets ridiculously low. I remember topping up the brake for the kid,
and he complained that there was air in the line. I told him, go up and sustain +6G, because
fluid goes down, and air goes up.

Sure enough, after he landed, it was perfect. Fluid down, air up.

Another time, Bob's Pitts had a flat right brake. No time to pull the armrest. Told him
the crosswind was from the right, so he only needed the left brake anyway. He asked,
what if I need to make a right turn? I told him, make a left 270 and off we went. He
was fine, and we topped the brake up after he landed.

That's just what BAD PEOPLE do, I guess. Topping up brake fluid is elementary work,
unless TC personally dislikes you, and then you don't get to live in Canada or own
property in Canada any more.

[Colonel]

a slow leak

generally that's a squared-off, hard old o-ring, which are cheap.

Over time, you will accumulate quite a stock of different sizes of them.

As Chuck would say, keep changing the rubber. Don't let it get old and
brittle.

You wouldn't believe how much maintenance (on all vehicles!) that aging
rubber causes - change those o-rings and hoses and belts!

[cgzro]

The Colonel seems to know a lot. Is this statement true about the hydraulic fluid?

"Brake caliper pistons apply hydraulic pressure when you push the pedals but there’s no retraction mechanism when you let off the pedals. The tolerance between brake pads and rotors is very small. As brake pads wear we add fluid to the system so that tolerance remains constant."

Thanks

There must be a little bit of retraction otherwise the brakes would drag and they don't. Most of the little master cylinders have a spring that you push against and which pulls back on the piston when you release the pressure, that has to cause a small bit of a vacuum above the brake puck which likely pulls it back a bit. Not sure, but its definitely only a one way system unlike systems that need powerful force in both directions that have a two way piston.

[Chuck Ellsworth]

As Chuck would say, keep changing the rubber. Don't let it get old and
brittle.

When they insist I wear a rubber I cut the ring off the condom and roll the ring on, they can feel the ring and think everything is just fine.

[Colonel]

It's amazing how much trouble rubber can cause.

I'm sure there are people reading this, that are here because the rubber broke.

Keep changing the o-rings and hoses and belts! There may be no regulatory requirement for you to do so, but the fucking things can't read.

I remember changing a magneto on a Citabria a few years back. The hoses were harder than granite. Tag said they were over 30 years old. I was afraid to touch them, in case they started to leak.

Is it really a good idea when your aircraft hoses - forward of the firewall! - are older than your girlfriend?! I suppose you could get an older girlfriend, but ....

My experience is that they deteriorate faster in the presence of heat and solvents, but I'm not very bright. Ask anyone.

[Chuck Ellsworth]

One of the most perplexing things about a lot of airplane owners is their inability to understand the need for replacement of hoses and seals, they seem to be unable to understand that proper ongoing maintenance saves tons of money in the long run.

P.S.

I don't use condoms Colonel because I tear them with the tire iron trying to get then on.