I am in the process of replacing all of my brake calipers and hoses on '73 1.7 that has been sitting for about 15 years.. From notes that I got from the previous owner says he changed to silicone brake fluid (many years ago). Fluid in the reservoir is kind of purple in color so I'm guessing its DOT 5 type.
Before I start pulling this fluid thru the new calipers, any reasons why I shouldn't just stay with DOT 5 fluid? Any downside to using DOT 5 in these cars?
Thanks for the comments
EJP914

DOT5 is so easy to contaminate and it likely is after sitting that long, I'd flush it all out and just use ATE Dot4.

dot 4 and dot 5 do not mix

do not use dot 5

It is probably ATE Super Blue. The Federal Government outlawed the sale of Blue brake fluid a year or so ago.

Flush the system with Dot4 fluid and go on about your merry way.

Clay

What fluid would you recommend to flush the system before refilling with DOT4?

I just use the same new good fluid to flush with.
it takes a little extra... but that way you know what the final boiling point will be rather than a mix

Just so I understand correctly. Put in DOT 4 and bleed the system. Eventually all of the DOT 5 will get pushed out. Any problem with any residual DOT 5 remaining in the hard line a nd proportioning valve?

I've always heard that dot 4 and dot 5 do not mix
that you have to disassemble the system to get the 5 out

my guess is... purple (or blue) is ATE dot4, in the old color they quit making
that is the only blue fluid I know of.

maybe use a turkey baster
take a little of the purple out of the reservoir
mix it in a butter tray with some new dot 4 and see if they mix or seperate

bet your old fluid is dot 4 also

https://www.jalopyjournal.com/forum/threads...-brakes.629650/

ATE Super Blue is DOT 4, not DOT 5 silicon. So it should be fine with any DOT 3 or DOT 4 fluid (except it dyed everything blue).

Don't use DOT 5 silicon unless you're willing to completely pull everything apart and completely flush out the old fluid. I wish they'd pull that crap from the shelves because it is not good stuff. Just don't.

I use Ford brake fluid inalmost everything. It's a solid DOT 4 fluid and works great. I think even the NAPA stuff in the big bottles is DOT 4.

And honestly, on the street, you'll never notice the temperature differences if you went with DOT 3. It's fine, too.

I have four bottles left of the Super Blue... I'd trade for a some cases of the good Brakleen (can't get it in CT any more...)

If it's a street car, what's wrong with DOT3 you can get from the local parts store? If I'm not mistaken, brake fluid is hydroscopic and should be flushed every year anyway.

I only buy the smallest little plastic bottles I can. Once you crack the seal, the clock starts to tick.

Do I actually flush fluid on all my cars every year. Yup, wife is the pedal pusher.

The significant rating difference between DOT 3 and DOT 4 is the "wet" boiling point. DOT 4 is higher.

"Wet" boiling point is the temperature at which the fluid will boil when it has absorbed all the moisture it can. Which means every Hyundai, Civic, Camry out there today.

DOT 4 actually absorbs moisture faster, so should be changed more often.

If you flush it regularly* DOT 4 is perfectly fine. If you're street driving, never tracking, and you'l let it ride for 5+ years, DOT 3 may be a better option.

I race on DOT 4 and change it a couple times a year. My street cars typically have DOT 3.

*I think "every year" is a bit anal...but at least I know I'm safe around you. My wife is my pedal pusher too. I just noticed that Harbor Freight as a vacuum bleed system that runs on shop air, I'm tempted to give it a try.

Genuinely confused by this stuff then...which is it? Bought it to have on hand at the new garage.

Anyone have a guess how it could be 3, 4, and 5.1?

It's DOT 5.1 (Backwards compatible with 4 & 3 )

Yes, just not dot5 silicone. They also say the flush interval recommendation is every 2 years with dot5.1 instead of 1 year for all others, excluding dot5. I have had dot5 in mine for over 20+ years and haven't had any issues. It's very purple and non-hygroscopic.

Probably my lack of skill, but I always make such a mess when I use a pressure bleeder. Wound up getting rid of mine years ago. But again, probably me, not the pressure bleeders fault.

Me too, I never liked them. But this one is a vacuum bleeder, using shop air (I have a compressor). Recommended to me by a good buddy. At $90 it's worth a shot.

https://www.harborfreight.com/merchandising...-kit-57057.html

Well, I will again be a heretic. I have three Porsches and one LBC. In that other world of Britishness it is common to use silicone oil (DOT5) brake fluid. You have to clean out all of the system from master to pipes and slaves, and then you can add the silicone. At least the one I buy is purple. It does not mix with the regular brake fluid, but in my experience it isn't affected by a few drops. It is not hygroscopic so it doesn't rust the parts and you don't have to change it as often. When you start to have a small herd of old cars that is a real bonus. Durn batteries and tires and other old parts keep you chasing maintenance.

It is said that the oil produces a mushy pedal. I will admit the standard 914 braking system takes some work to stop and doesn't need any added problems. Maybe. My TR6 has a vacuum booster, and drums in the back, so it isn't a perfect comparison. Still I run silicone in my TR6 and my son has it in his MGB and they both will lock up the wheels readily. I may feel a bit of spring in the pedal, but it might also be my imagination.

Got one, tried it tonight.

I made a mess.

Granted, I didn't use it completely correctly, so I'll give it another shot later. But it does not like the very small nipples on the Wilwood Dynalite calipers. More in tune with larger stock ones.