I am going to ask the moderator to remove the word preliminary from the title of this thread because the test is now complete and I can complete the write-up. The purpose of this test was to find answers for the continuing controversy about the use of DOT-5 silicone brake fluid in C2 and C3 brake calipers with O-ring conversions. The suppliers of these o-ring conversion kits and whole calipers equipped with o-rings or stock type lip seals now attach a disclaimer to their products announcing that the use of DOT-5 silicone fluid will void the warrantee. Many C2 and C3 owners like DOT-5 fluid because it will not hurt our expensive paint jobs and it prevents rust within the brake system without the need for periodic flushing, and we wonder if we really have to forgo the benefits of DOT-5 fluid if we want new calipers or o-ring conversions. Federal motor vehicle safety standard (No. 116) that sets requirements for all brake fluid, not just DOT-5, is obsolete because the only rubber compatibility requirement it imposes for SBR rubber. This was the common seal material 50 years ago. Since then EPDM rubber has become common, but brake fluid compatibility with it is not guaranteed by the FMVSS N0. 116 certification of any DOT brake fluid including DOT-5. We assume that most aftermarket brake equipment uses EPDM rubber, but we usually have no way of being certain. The rubber could be Chinesium.
My brake fluid compatibility test:
I intended to perform the more stringent of the 2 material tests in SAE J1703b (incorporated in FMVSS 116). It calls holding a rubber sample submerged in the brake fluid at 248 degrees F for 72 hours. The rubber sample was to be evaluated for swelling and changes in hardness following the exposure to heated brake fluid. The test is to determine if the test fluid is compatible with the predefined rubber samples. The rubber samples were the Red Silicone O-rings in the High Temperature O-ring conversion kit sold by ZIP, and two kinds of EPDM rubber O-rings I found in the same size as the in ZIP front kit. The test brake fluids were a 1977 Dow Corning preproduction Silicone fluid and the current Carquest brand DOT-5 fluid sold by regular auto parts stores.
I used an old toaster oven to heat small aluminum cans holding all three o-ring samples submerged in each brake fluid. I tried to use an infrared temperature sensor to calibrate the oven to 250 degree using an empty can as the target, and it seemed to call for a higher setting on the oven than I expected to yield 250 degrees. However, this turned out to be incorrect.
After 24 hours of heat in the toaster oven, I returned to the test site, and measured the sample cups to be about 335 degrees rather than 250 degrees. Since the EPDM rubber had a maximum 300 degree service temperature, I was afraid I had botched the test and would have to start again. I removed the sample cups from the oven and found the brake fluid to be discolored. I removed the O-rings, and found the red silicone o-rings to have failed dramatically. The ring tested in the 1977 fluid was grossly swollen and the ring in the Carquest fluid had turned to mush and broken into many pieces as shown in the photo. Surprisingly, Both EPDM rings in both brake fluids had not changed in cross section width and looked fine. The measurement technique is shown in the photos.
Despite testing at a much higher temp for the first 24 hours, I continued the test of the EPDM samples because they appeared to be compatible with silicone fluid in a tougher test than J1703b. I replaced the discolored fluid in each cup, and put the same EPDM o-rings back in each cup.
I tried to lower the toaster oven setting to keep the test cups at 250 degrees for the rest of the test. When I checked the samples after 24 hours I found that I was still overheating the samples at 270 degrees, so I lowered the toaster oven setting again. The Carquest fluid was discolored from purple to light brown, but the clear Dow Corning 1977 fluid has not changed much.
At the end of the third day, the test was completed. I checked the cup temperatures and they were only 220 degrees. I had over corrected the toaster oven. However, I think the test of one day at 335 degrees, one day at 270 degrees and one day at 220 degrees is much harsher than the correct J1703 test of three days at 248 degree, especially since the first day exceeded the temperature rating of the EPDM o-ring samples.
The change in the cross section width of the o-ring samples was the objective test criterion. I had no way of testing any hardness change in the EPDM o-rings, but there was no subjective change in their feel or appearance.
Results for Dow Corning 1977 pre-production fluid (a colorless experimental fluid that predated the DOT-5 spec)
1) Red Silicone O-ring from ZIP conversion kit -------- Original C/S = 0.207" After test, grossly swollen (see photo)
2)EPDM o-ring, sulphur cured (most common type)----Original C/S = 0.209" After test, C/S = 0.207"
3)EPDM o-ring, peroxide cured (more expensive)-------Original C/S = 0.209" After test, C/S = 0.208"
Results for Carquest Dot-5 brake fluid
1) Red Silicone O-ring from ZIP conversion kit -------- Original C/S = 0.206" After test, mushy and disintegrated (see photo)
2)EPDM o-ring, sulphur cured (most common type)----Original C/S = 0.210" After test, C/S = 0.210"
3)EPDM o-ring, peroxide cured (more expensive)-------Original C/S = 0.209" After test, C/S = 0.209"
Conclusions:
The Silicone o-rings (color coded red) are dramatically incompatible with silicone brake fluid.
EPMD o-rings are compatible with silicone brake fluid, both a commonly available brand of DOT-5 and a preproduction experimental fluid made in 1977. It is hard to understand why the Corvette aftermarket parts suppliers are so opposed to DOT-5 fluid, assuming their parts are made of EPDM rubber. That may be a "big if", and the companies at the retail level probably have no idea what kind of rubber seals they are selling.
There was a difference between the fluids in that the o-rings in the preproduction fluid actually had a very slight possible shrinkage while the o-rings in the DOT-5 fluid had no measurable change in cross section width. Also, the DOT-5 was much more destructive to the
red silicone rubber o-rings. It is likely in view of the silicone o-ring destruction that some swelling agent was added to the preproduction silicone brake fluid as it became a DOT-5 retail product. But there is no evidence that this amount of swelling agent is harmful to EPDM. In fact the Carquest DOT-5 prevented the slight shrinkage of the o-rings tested in 1977 preproduction fluid.
Bottom Line:
I am using the preproduction fluid in Lone Star o-ring calipers on my 1967 Corvette. I ignored the warning and gave up the warrantee for the benefits of Silicone brake fluid. I have had no problems in the 5 years since. I also put the preproduction fluid in my friend's 65 Corvette that had the ZIP regular o-ring (not red silicone) conversion kit. He has had no problems in about 4 years since.
I suppose these installations were a risk since we had no idea what the o-rings were made of. If I were doing another car, I would buy EPDM o-rings myself and discard the unknown o-rings from the supplier. You are giving up the warrantee anyway. I bought the o-rings used in this test from an online supplier: theoringstore.com They have an large range of sizes, metric and inch in EDPM that would surely match whatever size comes in your o-ring calipers. They are cheap too: the sulphur cured EPDM o-rings were 78 cents each, and the peroxide cured were $1.67.
My brake fluid compatibility test:
I intended to perform the more stringent of the 2 material tests in SAE J1703b (incorporated in FMVSS 116). It calls holding a rubber sample submerged in the brake fluid at 248 degrees F for 72 hours. The rubber sample was to be evaluated for swelling and changes in hardness following the exposure to heated brake fluid. The test is to determine if the test fluid is compatible with the predefined rubber samples. The rubber samples were the Red Silicone O-rings in the High Temperature O-ring conversion kit sold by ZIP, and two kinds of EPDM rubber O-rings I found in the same size as the in ZIP front kit. The test brake fluids were a 1977 Dow Corning preproduction Silicone fluid and the current Carquest brand DOT-5 fluid sold by regular auto parts stores.
I used an old toaster oven to heat small aluminum cans holding all three o-ring samples submerged in each brake fluid. I tried to use an infrared temperature sensor to calibrate the oven to 250 degree using an empty can as the target, and it seemed to call for a higher setting on the oven than I expected to yield 250 degrees. However, this turned out to be incorrect.
After 24 hours of heat in the toaster oven, I returned to the test site, and measured the sample cups to be about 335 degrees rather than 250 degrees. Since the EPDM rubber had a maximum 300 degree service temperature, I was afraid I had botched the test and would have to start again. I removed the sample cups from the oven and found the brake fluid to be discolored. I removed the O-rings, and found the red silicone o-rings to have failed dramatically. The ring tested in the 1977 fluid was grossly swollen and the ring in the Carquest fluid had turned to mush and broken into many pieces as shown in the photo. Surprisingly, Both EPDM rings in both brake fluids had not changed in cross section width and looked fine. The measurement technique is shown in the photos.
Despite testing at a much higher temp for the first 24 hours, I continued the test of the EPDM samples because they appeared to be compatible with silicone fluid in a tougher test than J1703b. I replaced the discolored fluid in each cup, and put the same EPDM o-rings back in each cup.
I tried to lower the toaster oven setting to keep the test cups at 250 degrees for the rest of the test. When I checked the samples after 24 hours I found that I was still overheating the samples at 270 degrees, so I lowered the toaster oven setting again. The Carquest fluid was discolored from purple to light brown, but the clear Dow Corning 1977 fluid has not changed much.
At the end of the third day, the test was completed. I checked the cup temperatures and they were only 220 degrees. I had over corrected the toaster oven. However, I think the test of one day at 335 degrees, one day at 270 degrees and one day at 220 degrees is much harsher than the correct J1703 test of three days at 248 degree, especially since the first day exceeded the temperature rating of the EPDM o-ring samples.
The change in the cross section width of the o-ring samples was the objective test criterion. I had no way of testing any hardness change in the EPDM o-rings, but there was no subjective change in their feel or appearance.
Results for Dow Corning 1977 pre-production fluid (a colorless experimental fluid that predated the DOT-5 spec)
1) Red Silicone O-ring from ZIP conversion kit -------- Original C/S = 0.207" After test, grossly swollen (see photo)
2)EPDM o-ring, sulphur cured (most common type)----Original C/S = 0.209" After test, C/S = 0.207"
3)EPDM o-ring, peroxide cured (more expensive)-------Original C/S = 0.209" After test, C/S = 0.208"
Results for Carquest Dot-5 brake fluid
1) Red Silicone O-ring from ZIP conversion kit -------- Original C/S = 0.206" After test, mushy and disintegrated (see photo)
2)EPDM o-ring, sulphur cured (most common type)----Original C/S = 0.210" After test, C/S = 0.210"
3)EPDM o-ring, peroxide cured (more expensive)-------Original C/S = 0.209" After test, C/S = 0.209"
Conclusions:
The Silicone o-rings (color coded red) are dramatically incompatible with silicone brake fluid.
EPMD o-rings are compatible with silicone brake fluid, both a commonly available brand of DOT-5 and a preproduction experimental fluid made in 1977. It is hard to understand why the Corvette aftermarket parts suppliers are so opposed to DOT-5 fluid, assuming their parts are made of EPDM rubber. That may be a "big if", and the companies at the retail level probably have no idea what kind of rubber seals they are selling.
There was a difference between the fluids in that the o-rings in the preproduction fluid actually had a very slight possible shrinkage while the o-rings in the DOT-5 fluid had no measurable change in cross section width. Also, the DOT-5 was much more destructive to the
red silicone rubber o-rings. It is likely in view of the silicone o-ring destruction that some swelling agent was added to the preproduction silicone brake fluid as it became a DOT-5 retail product. But there is no evidence that this amount of swelling agent is harmful to EPDM. In fact the Carquest DOT-5 prevented the slight shrinkage of the o-rings tested in 1977 preproduction fluid.
Bottom Line:
I am using the preproduction fluid in Lone Star o-ring calipers on my 1967 Corvette. I ignored the warning and gave up the warrantee for the benefits of Silicone brake fluid. I have had no problems in the 5 years since. I also put the preproduction fluid in my friend's 65 Corvette that had the ZIP regular o-ring (not red silicone) conversion kit. He has had no problems in about 4 years since.
I suppose these installations were a risk since we had no idea what the o-rings were made of. If I were doing another car, I would buy EPDM o-rings myself and discard the unknown o-rings from the supplier. You are giving up the warrantee anyway. I bought the o-rings used in this test from an online supplier: theoringstore.com They have an large range of sizes, metric and inch in EDPM that would surely match whatever size comes in your o-ring calipers. They are cheap too: the sulphur cured EPDM o-rings were 78 cents each, and the peroxide cured were $1.67.
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