Page 19 - WHITE BOOK

the master cylinder can yield misleading results. Testing for fluid properties at the wheels introduces a whole new set of opportunities for human error at each wheel.
A simple physical master cylinder test is likely the best course to take. Examination for introduction of contaminants by visual appearance of debris, cloudiness, presence of petroleum products and examination of the gasket seal at the master cylinder is a relatively simple and risk- free method.
MetalsandCorrosioninAutomotiveBrakeHydraulicSystems: Mostofthemetallicsurface areaofthesesystemsistheinternalsurfaceofthehydraulictubing. Thistubingisusuallymade of wound thin strips of steel braised together with a copper-zinc alloy. The spiral configuration of the steel allows for better consistency of the inner cross-section through the bends in the tubing. The braising alloy is selected to maintain a good bond with the steel while allowing enoughductilitytobend. Thecopper-zincalloycoatstheinnersurfaceofthetubingwhenitis new. Asthetubingisused,thecopperandzincarethefirstmetalstoappearinthefluid. The mainfacilitatorofthisslowoxidationisairinthesystem. Withage,theanti-oxidantinthefluid is degraded to the point where the copper in solution will plate out on exposed steel and cause pitting in the steel, both in various steel parts in the system and in the inner diameter (ID) of the tubing. When the anti-oxidant is degraded, this allows both the copper and any water in the system to go to work on the other metal components.
Reference A describes tests done in a laboratory environment to age the brake fluid in conditions similar to use in a vehicle and then testing various metals for corrosion as they are exposed to the fluids. The copper-zinc found in these tests was described as gel-like masses inside the pits formedintheironalloy.
Consideration of Elastomeric Components in Automotive Brake Hydraulic Systems: Brake hydraulics requires the use of elastomeric gaskets and seals to maintain system integrity between surfacesinrelativemotion. Thesematerialsincludenaturalrubber,styrene,butadiene,ethylene, propylenerubber,andpolychloroprene. Petroleumproductsreadilyabsorbintothesepolymers andcauseswellingthatresultsinfailure. Thesepolymersarealsoverysusceptibletoabrasion andtrappingtheabrasionproducts,thusacceleratingtheabrasion. Theproximityofthemaster cylinder opening to the other various fill openings for petroleum products makes the brake hydraulic system vulnerable to contamination. Failure at a wheel cylinder allows easy introductionofair,waterandaggressivecompoundslikeNaCl(salt)intothesystem. Anytest method should include a close examination of the master cylinder area before opening it, thorough cleaning prior to opening, a close examination of the appearance of the brake fluid (water, oil, etc.), and a close examination of bottom of the master cylinder reservoir, if visible, for particulate debris.
The prohibition of petroleum based fluids as brake hydraulic fluids results in most of these fluids being glycols, glycol ethers or mixtures of various glycol compounds. Water transports through these types of fluids very efficiently. Introduction of water will degrade the fluid, increase its viscosity, lower its boiling point and accelerate oxidation.
Test Plan and Conclusions: In an effort to evaluate the levels of contamination and fluid degradation of conventional brake fluids, the AMRA/MAP Fluids Taskforce submitted 23 used brake fluid samples obtained from the main reservoirs of automobiles with mileage ranging from 22Kto175Kmiles. Themaintenancehistoryofthesevehiclewasnotknown,theywererandom examples of used fluid. The initial test sequence was the analysis of the fluids for acidity, metallic constituents, RPC analysis SEM/EDS analysis.
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