The Federal standard (FMVSS 116) for brake fluid cites a 1971 SAE test (J1703b) for compatibility with rubber brake parts. However the only type of rubber tested is SBR rubber which was ubiquitous at that time for brake seals. Versions of SAE J1703 starting about 1990 included EPDM rubber as well as SBR rubber in the compatibility test. However, updates to SAE standards do not automatically update the Federal standards that cite them. There has to be a formal public rulemaking procedure which invites everly kind of objection including objections to government regulation in general. In 2010, NHTSA proposed updating FMVSS 116 with the later 2008 version of SAE J1703 which included the EPDM rubber compatibility test. But, the proposal was withdrawn in 2018.
That leaves FMVSS 116 without a test for compatibility with the currently most common brake seal material, EPDM. It is not just DOT-5 that is not certified for compatibility with EPDM. The same SBR compatibility test is all that is required of DOT 3, DOT 4, and DOT5.1 brake fluid as well. From a material compatibility standpoint, a FMVSS 116 certification is now pretty meaningless. To complicate things a little further, there is no requirement that vehicle manufacturers use either SBR or EPRM. They are not going to do anything really stupid with brake seals, but the owner's manual is the only source of information about the correct brake fluid for a modern car.
For aftermarket brake parts other than fluid, the only restraint is the possibility of a safety recall. If the parts are Chinesium, a maker in China does not fear a recall, but the American seller will be stuck with the bad stuff and maybe sued.
That brings me to the question we have discussed here. The sellers of restoration brake parts warn against using DOT-5 brake fluid. Is it just legal talk or do they know the seals will fail?
With many brake seals we don't know what the rubber is, and maybe the seller doesn't know for sure either. But with the O-ring type pistons we can buy our own O-rings and know the material if the piston seller cannot identify the material.
My own experience with Lone Star O-ring calipers is that I bought some for my 67 Corvette and ignored the DOT-5 warning. My silicone fluid has been in them about 5 years with no apparent problem, but I have not taken them apart for inspection. I also used my silicone fluid in another 65 Corvette with Lone Star O-ring calipers with similar good results.
Recently, just to look at it, I bought from ZIP an O-ring conversion kit (made by SS Corvette Brake Co.) with Silicone rubber O-rings for higher temperature performance. I thought maybe these red silicone rubber O-rings would be compatible for sure with silicone brake fluid, but now believe the opposite is true. I found an O-ring supplier with a huge selection and lots of technical information on their website. The red silicone O-rings they sold were rated as compatible with glycol based brake fluid but not silicone oil or grease. They had two types of EPDM rubber O-rings and both were rated compatible with glycol based brake fluid as well as silicone oil and grease. They had a compatibility chart for a very large number of liquids but silicone brake fluid was not included.
I bought both kinds of the EPDM O-rings and I intend to perform the SAE J1703 test on them and on the silicone O-rings from ZIP. The test calls for heating the rubber samples in a jar of brake fluid at 158 degrees and at 248 degrees for 72 hours, and evaluating the swelling and change or hardness. The O-ring performance chart rated excellent compatibility as less than 10% swelling in service. I still have to research the SAE criteria.
They silicone brake fluid I have been using has been an Dow Corning preproduction fluid from 1977 that I was given to test on a Corvette SCCA car that I pit crewed for. I will also do the material test on silicone fluid I just bought at Advance Auto Parts, so maybe the idea that DOT-5 fluid has changed over the years can be tested too.
My guess is that the EPDM O-rings will pass the test in both kinds of silicone fluid, and that they are the same type used by Lone Star. But that is just a guess until confirmed. Other curious NCRS members may want to do this test also. Good luck fellow scientists.
That leaves FMVSS 116 without a test for compatibility with the currently most common brake seal material, EPDM. It is not just DOT-5 that is not certified for compatibility with EPDM. The same SBR compatibility test is all that is required of DOT 3, DOT 4, and DOT5.1 brake fluid as well. From a material compatibility standpoint, a FMVSS 116 certification is now pretty meaningless. To complicate things a little further, there is no requirement that vehicle manufacturers use either SBR or EPRM. They are not going to do anything really stupid with brake seals, but the owner's manual is the only source of information about the correct brake fluid for a modern car.
For aftermarket brake parts other than fluid, the only restraint is the possibility of a safety recall. If the parts are Chinesium, a maker in China does not fear a recall, but the American seller will be stuck with the bad stuff and maybe sued.
That brings me to the question we have discussed here. The sellers of restoration brake parts warn against using DOT-5 brake fluid. Is it just legal talk or do they know the seals will fail?
With many brake seals we don't know what the rubber is, and maybe the seller doesn't know for sure either. But with the O-ring type pistons we can buy our own O-rings and know the material if the piston seller cannot identify the material.
My own experience with Lone Star O-ring calipers is that I bought some for my 67 Corvette and ignored the DOT-5 warning. My silicone fluid has been in them about 5 years with no apparent problem, but I have not taken them apart for inspection. I also used my silicone fluid in another 65 Corvette with Lone Star O-ring calipers with similar good results.
Recently, just to look at it, I bought from ZIP an O-ring conversion kit (made by SS Corvette Brake Co.) with Silicone rubber O-rings for higher temperature performance. I thought maybe these red silicone rubber O-rings would be compatible for sure with silicone brake fluid, but now believe the opposite is true. I found an O-ring supplier with a huge selection and lots of technical information on their website. The red silicone O-rings they sold were rated as compatible with glycol based brake fluid but not silicone oil or grease. They had two types of EPDM rubber O-rings and both were rated compatible with glycol based brake fluid as well as silicone oil and grease. They had a compatibility chart for a very large number of liquids but silicone brake fluid was not included.
I bought both kinds of the EPDM O-rings and I intend to perform the SAE J1703 test on them and on the silicone O-rings from ZIP. The test calls for heating the rubber samples in a jar of brake fluid at 158 degrees and at 248 degrees for 72 hours, and evaluating the swelling and change or hardness. The O-ring performance chart rated excellent compatibility as less than 10% swelling in service. I still have to research the SAE criteria.
They silicone brake fluid I have been using has been an Dow Corning preproduction fluid from 1977 that I was given to test on a Corvette SCCA car that I pit crewed for. I will also do the material test on silicone fluid I just bought at Advance Auto Parts, so maybe the idea that DOT-5 fluid has changed over the years can be tested too.
My guess is that the EPDM O-rings will pass the test in both kinds of silicone fluid, and that they are the same type used by Lone Star. But that is just a guess until confirmed. Other curious NCRS members may want to do this test also. Good luck fellow scientists.
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