Anyone switch to "Dot 5" brake fluid?

[yechave]

Came across this on one of the tech shows on tv last week. Wondered if anyone is using this. "DOT 5 is silicone chemistry."

http://www.xs11.com/tips/maintenance/maint1.shtml

[bigbear]

Be very careful, The company i work for was doing testing with silicone based hydraulic fluids and found this fluid required different seal materials. I am not sure if DOT 4 seals will work with DOT 5.
Also silicone is compressible. The reason silicone was beings used was for temperature range.

Roy

[Dick]

Be very careful, The company i work for was doing testing with silicone based hydraulic fluids and found this fluid required different seal materials. I am not sure if DOT 4 seals will work with DOT 5.
Also silicone is compressible. The reason silicone was beings used was for temperature range.

Roy
Yup - the big boyz disapprove of DOT 5 brake fluid as a conversion fluid in a system set up and using DOT 4. We have an article on the subject around here somewhere - I'll see if I can find it.

[jzeiler]

I never base a decision on 13 year old information. But 13 years ago I did consider it for my MGB and decided it was way too much hassel to completely flush out the dot 3 and then change all the natural rubber seals to some that were compatible to the silicon dot 5.

[Morley]

I am not sure if DOT 4 seals will work with DOT 5.

Don't think so. Dot 3 and 4 are pretty much interchangeable, you can go from 3 to 4 but they don't recommend you go from 4 to 3. So, the seals would need to be replaced for Dot 5.

[petepeterson]

DOT 3, DOT 4, and DOT 5.1 are all glycol based fluids..... DOT 5 is synthetic fluid so don't mix it with the others...HD is the only bike manufacturer that uses DOT 5... It aireates bad so ya got to let it sit for awhile before you pour it in the reservoir

But really,, why change????? DOT 4 is as good as any............Pete

[dshealey]

As others have said, DON'T TRY IT! To do so you would have to COMPLETELY clean the entire system out so not trace of the DOT 4 remains, a daunting task to say the least. Then you would have to worry about seal compatibility. As well as I remember though, the rubber parts were not an issue with DOT 5. Silicone is less reactive than the Glycol based DOT 4.

The silicone fluids were developed for heat resistance mostly, and used in high performance brake systems. It is not a panacea, and really does nothing for the normal street driver. In fact, it has a rather serious drawback for most street systems. Moisture will not be absorbed into it, and will eventually puddle at the lowest points in the system, where it will cause corrosion. DOT 3/4 will absorb small amounts of moisture and not let it pool in small spots.

The new DOT 5.1 is compatible though, just a shame that they did not call it DOT 6 to prevent people from ruining brake systems in the future by putting DOT 5 in systems that have DOT 5.1 in them! As DOT 5.1 becomes more used, that danger will increase.