How often to change brake and landing gear fluids?

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peter-h

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peter-h
What is the actual life of this stuff?

The legal requirements vary, and here in the UK most maintenance firms never change the fluids (regardless of what the maintenance manuals say); only top them up as necessary.
 
peter-h said:
What is the actual life of this stuff?

The legal requirements vary, and here in the UK most maintenance firms never change the fluids (regardless of what the maintenance manuals say); only top them up as necessary.
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Just follow the manufacturers recommendations.
 
AFaIK unlike automotive brake fluid, the hydraulic fluid used in aircraft brake systems is not hygroscopic (affinity for water) and therefore doesn't degrade or need replacement periodically.
 
The recommendation for me is every 3 years for both fluids.

I know it's never been done :) (8 years). Never had a problem, but then the airplane is hangared. Time to do it, I think.
 
gismo said:
AFaIK unlike automotive brake fluid, the hydraulic fluid used in aircraft brake systems is not hygroscopic (affinity for water) and therefore doesn't degrade or need replacement periodically.
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5606 is pretty much just a low viscosity mineral oil which means it will eventually oxidize and change properties. How long will that take? I don't know but I expect it to be many, many years. Keep the system clean and the oil should provide very long service. I expect just the make-up fluid added when seals and hoses are changed is enough to keep the additive package up to required performance levels.

Used in nitrogen charged struts, it'll probably last the life of the strut.

I've reviewed the service history of my 30 year old Dakota pretty closely and don't recall any brake fluid changes. I've bled the brakes and the color and odor of the old fluid was the same as the new make-up fluid. I'm certainly not rushing out to change the brake fluid any time soon...
 
Cessna has a procedure to check the fluid in their landing gear systems. If it has darkened, it needs checking with a bit of shiny copper, IIRC. If the copper discolors, the fluid has become acidic or something. Im a long way from the shop today and can't look it up.

Small amounts of water can get past the brake caliper piston seals, mix with the oil, and start corrosive chemical reactions. The brakes should really be dismantled and cleaned up every few years. They're not built nearly as weatherproof as automobile brakes.

Dan
 
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