Dot 5 silicone compatibility

[paulswagelock]

My 65 mustang blew the rear rubber brake line. After 46 years I guess it was time. It still had the original single bowl master cylinder, so I figured since the system was down, time to change it to a dual bowl (safety over period correctness since i don't show it much). The previous owner converted to Dot5 silicone fluid many many years ago. While researching, I found numerous stories and warnings about trying to convert back to Dot 5.1 that I decided to leave it alone and refill with Dot5. Other than $50 in brake fluid, no big deal.
MC swap went easy, bleeding was easy.

Question is, what is the truth on converting back? Would it have been possible to flush the silicone and go to 5.1 or was staying the course the only option without changing all the remaining brake components?

 

[EricF]

I've always assumed once you have dot 5 you can simply flush the lines out with whatever else and you're ok.

 

[97prizm]

Converting back to dot 4 or 5.1 is a nightmare. You must replace all hoses master cylinders etc, the entire braking system as dot 5 will not mix well with other brakefluids. If you want to go back you'll be in for some expense and time consuming work. I've worked on race cars and other cars and will say that dot 5 and other fluids are absolutely not compatible as most are glycol, and dot 5 which is silicone based.

 

[mechtech2]

For all the trouble to do it right [conversion], it is best o leave the 5.0 in there.

But it makes me wonder if the original swap to 5.0 was done right!

 

[oliveoil]

Go back to oem Dot3. Dot5 is not compatible with anything. Flushe the system good with lots of Dot3.

 

[paulswagelock]

The Dot 5 has been in there for well over a decade and a half with no issues at all. So, I assume it was flushed correctly. When I bled the brakes, the old fluid was crystal clear, no gunk, rust pieces, etc. This is a garage queen car - sunny days, no rain or snow in 30 years.
It sounds like it is far riskier to try to flush and return to glycol based fluid then to leave it be.

 

[zrxkawboy]

I love the DOT 5 in my older cars. I would use it in everything, but it's not supposed to be used in ABS.

I would recommend keeping DOT5, but if you must switch, just switch. When I convert a car to DOT 5, I just suck as much old fluid out of the MC as I can, fill it with DOT 5, and bleed the system til I see purple at each wheel. No "nightmare" at all, and never any problems.

 

[zrxkawboy]

Here's some more info:
http://www.moparaction.com/Tech/quest/BINDER_JUICE.html