Fairchild Club Forum

' Good  afternoon,   All the struts on my PT-19 have been apart and are clean and dry....   What is the best type fluid to use..   I appreciate your thoughts...   Thanks,  John  '

'
Hello John,

The old blue colored Mil Spec fluid is no longer available. Now is the time to switch to the standard MIL-H-5606 red petroleum based hydraulic fluid used in over 90% of all light aircraft hydraulic systems, including brakes from the end of WWII to present. If you have cleaned and rebuilt your brake system this is a good time to make the same switch there. DOT 3/4 brake fluid is tough on paint and life limited to 2 years and reservice. DOT 5 silicon has it's own problems which are primarily the same reason people tend to use it in the first place. DOT 3/4 actually absorbs moisture so it becomes less able to cope with heat which is why it must be changed every 2 years. DOT 5 does not absorb moisture but instead the moisture descends to the low points in your system (read wheel cylinders here) and starts a corrosion process. Also once aerated it is physically impossible to separate all air from silicon DOT 5 fluid which will always leave a soft feeling in the pedal. Take a little time and review the many professional web sites that treat this topic in more detail.'

' My understanding is they have replaced 5606 with a less flammable version called MIL-PRF-83282. 
5606 is still the old standard and will work just fine.
Sent from my iPad Mini

On Jan 21, 2014, at 17:27, "wsknettl@centurytel.net" wrote:

 

Hello John,

The old blue colored Mil Spec fluid is no longer available. Now is the time to switch to the standard MIL-H-5606 red petroleum based hydraulic fluid used in over 90% of all light aircraft hydraulic systems, including brakes from the end of WWII to present. If you have cleaned and rebuilt your brake system this is a good time to make the same switch there. DOT 3/4 brake fluid is tough on paint and life limited to 2 years and reservice. DOT 5 silicon has it's own problems which are primarily the same reason people tend to use it in the first place. DOT 3/4 actually absorbs moisture so it becomes less able to cope with heat which is why it must be changed every 2 years. DOT 5 does not absorb moisture but instead the moisture descends to the low points in your system (read wheel cylinders here) and starts a corrosion process. Also once aerated it is physically impossible to separate all air from silicon DOT 5 fluid which will always leave a soft feeling in the pedal. Take a little time and review the many professional web sites that treat this topic in more detail.
'

'
A couple of newer Mil Specs have superseded 5606 but 5606 is till a maintained spec and is still readily available. Unless you have issues with your hydraulic system flluid being exposed to extreme high temps there's no need to hunt for the later derivatives.

Common petroleum-based:Mil-H-5606: Mineral base, flammable, fairly low flashpoint, usable from ?65 °F (?54 °C) to 275 °F (135 °C), red colorMil-H-83282: Synthetic hydrocarbon base, higher flashpoint, self-extinguishing, backward compatible to -5606, red color, rated to ?40 °F (?40 °C) degrees.Mil-H-87257: A development of -83282 fluid to improve its low temperature viscosity.'

'At OSH last summer the Cleveland reps were asked their take on the 83282. They are fine with it, but want you to change the O rings to Viton, I believe it was. This subject seems to have become more popular due to some brake fires on Cirrus aircraft, I've heard.
Bill McC

Sent from my iPad

On Jan 21, 2014, at 7:43 PM, wrote:

 

A couple of newer Mil Specs have superseded 5606 but 5606 is till a maintained spec and is still readily available. Unless you have issues with your hydraulic system flluid being exposed to extreme high temps there's no need to hunt for the later derivatives.

Common petroleum-based:[*]Mil-H-5606: Mineral base, flammable, fairly low flashpoint, usable from ?65 °F (?54 °C) to 275 °F (135 °C), red color[*]Mil-H-83282: Synthetic hydrocarbon base, higher flashpoint, self-extinguishing, backward compatible to -5606, red color, rated to ?40 °F (?40 °C) degrees.[*]Mil-H-87257: A development of -83282 fluid to improve its low temperature viscosity.
'