 You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
Hope Mini brake bleeding...
Upon internet stumbling, for years I've been using 5 DOT AP Lockheed car brake fluid, with no major problems. Looking at bleeding them today, apparently I should have been using 5.1 DOT on my first gen Hope mini's.
I've not noticed any poor performance of such over the many years of having the wrong fluid in.
I'm a bit puzzled as all articles I've read say I would have knackered all my seals and should flush out my old DOT 5?
Have I just been really lucky and they're due to gush any day?
DOT5 is silicone based.
It has it's own downsides but it's 100% compatible with DOT 3/4/5.1 which are glycol-based.
The downsides are it won't mix with water, which means any water in the system will collect at low points (in a bikes case the caliper) and potentially cause corrosion. This also means that water in the caliper has the potential to boil. It's also hard to bleed the water out as there isn't a low point to bleed it from (because normally you just have to deal with bleeding air from high points).
Also I don't think it's miscible with the other DOT fluids, so if you change it now you'll have to disassemble each part and clean it out, flush the hoses etc.
The advantages are:
It's not hygroscopic, so if the seals do actually work 100% then it won't absorb water from the atmosphere and degrade over time. But the seals aren't perfect, especially on an MTB where they're designed to move a lot further than a car or motorbike where the pads barely move when the pedal is pressed.
It is (generally) compatible with paint so won't damage it when you spill it.
Dot 5 is very different to 5.1, it made from different stuff. You should never mix them. As to whether it is worth changing, I probably wouldn't if it has been working for a long time. If you do then you'll need to get rid of the dot 5, I don't think a flush would be enough to get it all out. I've no idea what the perils of mixing them are but every article about brake fluid in cars says not to mix them.
DOT 5 is silicone based, not mineral oil based. It's mineral oil that destroys the seals. AFAIK, you can replace DOT 4 or DOT 5.1 with DOT 5, but you are supposed to completely flush all the old fluid out because they won't mix.
Ta, helped me decide to go the way I've always gone!