Hi Dyke,We have a couple of vehicles (64 sport and 61 Willys pickup) where I replaced the master and all wheel cylinders and hoses but kept it Dot3, before I was aware of the benefits of Dot5. If I can convert these to Dot 5 without replacing everything all over again that would sure be nice. I was under the impression you had to replace hoses and wheel cylinders, even the master cylinder, and flush all hard lines with alcohol or some solvent when converting. That way it’s pretty well like starting from new. If you’re saying the system will tolerate just flushing and bleeding Dot5 until you are basically seeing purple, I would do it. For some reason I was under the impression that anything that has Dot3 already in any rubber seal should be replaced.D&KSent from my iPhoneOn Jul 3, 2024, at 17:03, Dyke Ridgley <ridgley...@xxxxxxxxx> wrote:We have had another round of member discussion regarding DOT 5 brake fluids, so I wanted to separate my comments from other threads about master cylinders, etc.Everybody has opinions on DOT5 brake fluid. This has been my personal experience:
1. I have converted over 150 cars to DOT5 since 1977.
2. I have only had two issues. On two cars with Brand New master cylinders with new “tight” seals, both cars’ brakes had a millisecond delay in releasing. Just enough delay that you noticed it. I converted them back to DOT3/4 and the issue went away. Now that the cars both have years of usage, and the seals have settled into the cylinders, I am sure a DOT5 conversion would have no problems.
3. I have never flushed a brake system prior to DOT5 conversion. I drain the system, add DOT5 and bleed until I have 95% DOT5 exiting the system. Never had a problem with mixing fluids.
4. Dow Corning did extensive testing with mixing DOT5 and DOT3 fluids and found no resulting issues.
5. Don’t shake or drop the container of DOT5 fluid. It aerates easily and it takes some time for the air to leave the fluid.
6. My bleeding method of preference is “gravity”, with vacuum bleeding next and “pumping” the pedal as a last hope (see Item 5 above).
7. It makes no difference which corner of the car you bleed first. I start at the corner closest to the master cylinder to get new fluid through the master as quickly as possible.
8. I change DOT5 fluid every 10 years because I feel guilty and to continue to remove any remaining DOT3/4 fluid from the system. I change conventional fluids every five years.
9. DOT5 fluid will not work in ABS systems due to the higher viscosity of DOT5 not being able to pass through the microvalves in the ABS controllers.
10. We DO NOT use DOT5 fluid in our race cars. It has a high temperature “window of compressibility”. Below that temp the pedal is hard, but within the temp “window” you get a spongy pedal. Not a good thing on a race car.
11. If people complain about a “spongy” pedal with DOT5, they have not done a good bleed of the system or are not bleeding the brakes correctly. DOT5 will give just as good a pedal feel as any other fluid. I have NEVER encountered a “spongy” pedal using DOT5.
Remember, before you start yelling and screaming, this has been my experience and your results may vary.
Dyke Ridgley
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