Simple question
Can I use fluid designed for cars/motorbike (dot 5.1)…
Or does it need to be cycle specific

What brakes?

Some use dot 5.1 or maybe 4, e.g. Avid brakes. Some use mineral oil, weight may vary.

Dot 5.1 you can use the car stuff, though while the big bottles are far less of a rip off than the bike specific bottles and is the same stuff, supposedly the stuff reacts with moisture in air once opened so if you don’t use the remains for a long time it may be no good when you do come to use it. Not sure that’s true or just what people repeat having read it somewhere.

Mineral oil, just find the weight you need.

It does NOT need to be bike specific. I bought some motorcycle Motorex branded DOT 5.1 for my Avid brakes. Less than 1/2 the price of the bike stuff, and available locally.

DOT will destroy brakes that are made for mineral oil, though. They’re not interchangeable. (Shimano, Magura, for example use mineral oil)

So long as the bottle top is on properly the Dot fluid can only absorb the tiny amount of moisture in the air inside the bottle, which can be reduced by squeezing the bottle before you put the top on.

Dot 5.1 has a higher boiling point (when new) than Dot 4 at the expense of being more hygroscopic, so should be changed more frequently.

Hope, x2 evo front. V2 rear. Bought them both used but nearly new. Want to swap calipers also put new braided hoses on.
Looked at the you tube how to vids. I’m pretty sure I can do it all myself. Looking on ebay at fluid. Some decent shell 5.1 is around £7 per litre but it’s in car section.
Also unsure whether I should / can swap the levers?
I know the evo lever is newer /better, and more suited for use on the front, but it would be easy enough to switch them in the future!
Think I will just keep them paired up as they came for now.

Looking on ebay at fluid. Some decent shell 5.1 is around £7 per litre but it’s in car section.

Just pop into your local motor factors or halfords and pick some up. The Type is the Dot 5.1 do not use Dot 5 it is not the same. There is no such thing as bike specific Brake Fluid it just the same stuff in a different bottle.

Drop hope a quick e-mail for confirmation on the swap, they are really helpful.

Dot 5.1 has a higher boiling point (when new) than Dot 4 at the expense of being more hygroscopic, so should be changed more frequently.

Not always, some dot 4 fluids have a higher boiling point than 5.1 😉

I wouldn’t buy as much as a litre unless you’re planning on using some in the car as well, it doesn’t keep forever on the shelf. I’ll stick my neck out and say that it’s available in ANY petrol station, no need to go to any special shops!

Watch your furniture with DOT 5.1. It’s really very nasty stuff. Eats through everything.

Halfords sell a small bottle of their own brand, in the cars section- it’s expensive by volume but it’s a pretty sensible size for bikes.

I’ve never been too paranoid about using unopened bottles, tbh, I can see the reasoning but in practice if you close up the bottle as quick as you can and store it somewhere dry, water contamination shouldn’t be too big an issue. But it’s not best practice, that.

On the v2, how do I get an over extended piston to go back in

If it’s clean and in good condition, just pushing it back in should do it. Though if you’re unlucky you can damage the seals.