Since I replaced everything in this 68 Mustangs braking system I figured I would tear down the distribution block and proportioning valve.
1. Inside of the distribution block there is a spool that has three O-rings on it. I noticed that two of them were the square type and one was round. Would it make a difference if I use all round O-rings or should I try to find square ones?
2. I bought a kit to rebuild the stock proportioning valve and noticed that the O-rings are made of Viton. Would this be ok to use with DOT 3 brake fluid or should I replace them with EPDM O-rings?
Looks to me that the Viton is a no good with DOT type 3 fluid and I should use the EPDM. Anyone think otherwise?
EPDM (Ethylene Propylene, EPM)
EPM is a copolymer of ethylene and propylene. Ethylenepropylene-diene rubber (EPDM) is produced using a third monomer and is particularly useful when sealing phosphate-ester hydraulic fluids and in brake systems that use fluids having a glycol base.
Heat resistance
Up to 300°F (149°C) (max. 400°F (204°C) in water and/or steam).
Cold flexibility
Down to approximately –70°F (–57°C).
Chemical resistance
Hot water and steam up to 300°F (149°C) with special compounds up to 400°F (204°C)
Glycol based brake fluids up to 300°F (149°C)
Many organic and inorganic acids
Cleaning agents, soda and potassium alkalis
Phosphate-ester based hydraulic fluids (HFD-R)
Silicone oil and grease
Many polar solvents (alcohols, ketones, esters)
Ozone, aging and weather resistant.
Not compatible with:
Mineral oil products (oils, greases and fuels).
Viton (Fluorocarbon, FKM)
Fluorocarbon rubber has excellent resistance to high temperatures, ozone, oxygen, mineral oil, synthetic hydraulic fluids, fuels, aromatics and many organic solvents and chemicals. Low temperature resistance is normally not favorable and for static applications is limited to approximately –15°F (–26°C) although in certain situations it is suitable down to –40°F (–40°C). Under dynamic conditions, the lowest service temperature is between 5°F and 0°F (–15°C and –18°C). Gas permeability is very low and similar to that of butyl rubber. Special fluorocarbon compounds exhibit an improved resistance to acids, fuels, water and steam.
Heat resistance
Up to 400°F (204°C) and higher temperatures with shorter life expectancy.
Cold flexibility
Down to –15°F (–26°C) (some to –40°F (–40°C)).
Chemical resistance
Mineral oil and grease, low swelling in ASTM oil No. 1, and IRM 902 and IRM 903 oils
Non-flammable hydraulic fuels in the group HFD
Silicone oil and grease
Mineral and vegetable oil and grease
Aliphatic hydrocarbons (fuel, butane, propane, natural gas)
Aromatic hydrocarbons (benzene, toluene)
Chlorinated hydrocarbons (trichlorethylene and carbon tetrachloride)
Fuels, also fuels with methanol content
High vacuum
Very good ozone, weather and aging resistance.
Not compatible with:
Glycol based brake fluids
Ammonia gas, amines, alkalis
Superheated steam
Low molecular organic acids (formic and acetic acids).
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