lube on brake fittings?

[prkaye]

For the fittings on the cleveland brakes, should any lube be used, or should they be installed dry? Is fuel lube OK?

[mannanj]

Phil:

I would use some sort of anti-sieze compound on the pipe thread fittings. Fuel Lube, I believe states on their container that it is good for anti-sieze use in aluminum. (Double check, I could be wrong.)

For the AN flare fittings Fuel Lube would be ok, but probably not totally necessary

[alpinelakespilot2000]

Bakerseal or some other teflon PASTE works good here. Of course do NOT use teflon tape.

I've always heard that AN flare fittings should always be fitted dry--only NPT threads use fuel lube or paste of some sort.

[roee]

I asked Matco tech support a while back what sealant to use on the NPT threads in the brake system. They recommended Loctite 567.

As has already been said, that's for NPT threads only. Do not use any sealant on flared fitting connections.

-Roee

[mburch]

Originally Posted by alpinelakespilot2000

I've always heard that AN flare fittings should always be fitted dry--

To add to what Steve said... I usually put a small dab of fuel lube (aka EZ-Turn) on the threads of a flare fitting connection to prevent galling - but never anything on the mating surfaces. The seal is formed by the mating surfaces of the flare fittings making hard contact, so you don't want to put anything on there.

mcb

[Dave Cole]

From the LOCTITE technical data sheet:

"LOCTITE 567 is designed for the locking and sealing of metal tapered threads and fittings. The product cures when confined in the absence of air between close fitting metal surfaces and prevents loosening and leakage from shock and vibration. The high lubricating properties of this compound prevent galling on stainless steel, aluminum and all other metal pipe threads and fittings."

[G-force]

567 is all we have used for over 10 years of assembling fuel and oil systems, and prevent galling on stainless to stainless hardware. You could not pay me to use something else.

[Jimd]

What about lube on the pins that the inside pads slide on? I thought maybe they would be getting better by now.

It seems like after I use the brakes on landing they get heated up (not more than I would expect but then they do not want to release?)

I can get the airplane rolling straight down the taxiway and take my feet off and tell they are dragging. I also notice that all the sudden they sometimes DO release and it feels like someone just gave me a big push!

After they cool down the are fine, in fact for the first flight of the day, as I taxi out I can hear them rattle and the nosie stops as I apply brake pressure. The noise occurs at each tar strip in the taxiway at slow taxi speeds.

[Lycosaurus]

Originally Posted by Jimd

What about lube on the pins that the inside pads slide on?

I was told to use a dry lubricant by the factory such as graphite. I found a graphite spray at our hardware store. Actually looks and goes on like black paint.

[robpar]

As a licensed auto mechanic you NEVER NEVER NEVER NEVER use grease on ANY hydraulic brake component. There are special approved Silicon base lubes that can be used on components that contact brake fluid. For the sliding parts of the caliper there are also special lubes that do not drip when they get hot. These are available at most Auto Supply outlets as well as dealerships. Generally one does not lube the pins that go through the brake pads as you do not want any of that lube to drip onto the pads.

I know that aircraft use hydraulic fluid in their brakes and that a thread exists on this topic. Using flammable oil based brake fluids certainly goes against all my training and I will have to deal with that when I get there. The above lubes are compatible I'm sure with hydraulic fluid seals but check that first.

A common cause of brakes dragging after they have heated up is the length of the master cylinder push rod being a bit too long. When the fluid heats up the rod it gets a little longer and the piston can not retract far enough and the compensation port in the master cylinder is covered and the pressure in the system does not release fully. I have had customers, especially in old Volkswagens, adjust their brakes with this push rod and the brakes then lock on. Most domestic manufacturers do not make this adjustable but I do not know about aircraft brakes. It is worth checking to make sure that the length is correct.

Bob Parry