This page was last updated on $Date: 2000/03/06 00:01:08 $

DOT 5 Brake Fluid

Mike Burdick (on the SOL list) says:

A while back when this topic came up, I posted excerpts from a Skinned Knuckles article on silicone brake fluid. They made the best attempt I've seen so far to actually address this issue with hard data instead of anecdotes. The data they used came from military tests in jungle conditions and tests from the original producer of DOT5 fluid (DuPont? I can't remember...). Even so, they were not able to come up with many conclusions about DOT5 fluid. In a nutshell, the conclusions were:

  1. DOT5 does not absorb water and may be useful where water absorption is a problem.

  2. DOT5 does NOT mix with DOT3 or DOT4. They also maintain that all reported problems with DOT5 are probably due to some degree of mixing with other fluid types. They said the proper way to convert to DOT5 is to totally rebuild the hydraulic system.

  3. Reports of DOT5 causing premature failure of rubber brake parts were more common with early DOT5 formulations. This is thought to be due to improper addition of swelling agents and has been fixed in recent formulations.

  4. DOT5 is compatible with all rubber formulations.

  5. DOT5 doesn't eat paint.

They also made some general recommendations based on this data and personal experiences. These, along with recommendataions of list members included:

  1. If it works for you, use it. You won't hurt anything if you do the conversion correctly. (See, #2 above)

  2. Careful bleeding is required to get all of the air out of the system. Small bubbles can form in the fluid that will form large bubbles over time. It may be necessary to do a series of bleeds.

  3. DOT5 is probably not the thing to use in your race car although it is rated to stand up to the heat generated during racing conditions. The reason for this recommendation is the difficult bleeding mentioned above.

  4. DOT5 is a good choice for the weekend driver/show car. It doesn't absorb water and it doesn't eat paint. One caveat is that because it doesn't absorb water, water that gets in the system will tend to collect at low points. In this scenario, it would actually be promoting corrosion! Annual flushing might be a good idea.

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