| Brake fluid and moisture [message #155945] |
Sun, 08 January 2012 14:14  |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
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Senior Member |
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As I was reading the thread on dot 5 fluid the message seemed to say the best fluid for our units is dot 5, and therefore anything else is not best. Wait a minute!! The brake hydraulic system actually has a constantly changing fluid volume due to temperature expansion, pad and shoe wear, stretching brake hoses, and moisture. Tiny amounts of air in the system also compress. Air is the medium that makes up the differences in this volume through the changing levels in the reservoir. Mostly, air gets into and is expelled in the system through the master cylinder reservoir and even a little past seals Yes, tiny amounts of air gets into the system due to sepage past seals (not enough to make brakes unusable however, but enough that over a long period of time must be dealt with). This air will have moisture and as temperatures drop will condense in the brake system. Hense water in the system. Water causes rust, pitting in cylinders and lines, and sludge. All bad things in the system. Some of you have even experienced rusted through brake lines in our 35 year old machines. (I have)
Dot3 and dot4 fluids allow the water to chemically combine with the fluid and disperse throughout the system through the movement of fluid while using the brakes to prevent the sludge, rust, and pitting. Pretty good thing right? Once the fluid absorbs all that it can, it is known to be wet and can no longer do it's job properly. (we want to be sure we flush the system before this point). Vehicles that sit for long periods of time are worse. ( topic for another discussion).
Dot5 fluid does not absorb moisture therefore the water stays as a separate component and pools in parts of the system, allowing the water to do it's damage starting immediately. Car collectors and race drivers use these to avoid some of the breathing absorption while their vehicles sit. But must flysh regularly Dot5 actually needs more frequent flushing than dot3 or 4. The difference between 3 and 4 is the boiling point when wet. Another problem with moisture.
All types of fluids need flushing and replacement on a regular basis. The time between these is a matter of opinion I suppose, but recommendations by the manufacturers will keep you out of trouble.
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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