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DOT5 is silicone based and not hygroscopic. It doesn't attract moisture. It's non-corrosive. If you put DOT5 in the system, you can leave it there. It's quite a bit more expensive than DOT3 or 4.

There's almost zero substantive difference between DOT3 and DOT4. If I were going in that direction, I'd use the 3.

But, from everything I've read, I'd go with DOT5.

If the system is NEW, and I mean NEW, and all components are bone dry and clean, I'd be inclined to use DOT5. 

If any part of the system is used, like the metal brake lines, I'd just go DOT 3/4(usually labeled as such, I use Valvoline Synthetic 3/4) and change it every 2 years like you're supposed to. The problem is nobody changes it. Come to think of it, I built my Spyder in 2017 and didn't flush last year, as the engine and trans got rebuilt last summer. So it's on my to-do list for this spring.

DOT 5 is NOT compatible with even a trace of regular brake fluid.

Gordon Nichols posted:

Or just leave what'cha got in there like all of us do in our daily drivers for 10 - 15 years.

Jus' Sayin'..........

I mean......    Do you think and anyone ever changed brake/hydraulic fluid in an old Volkswagen Beetle during the life of the car?

But that's why they had to replace or rebuild all the hydraulic parts, MC, and wheel cylinders. If you change the fluid every two years, you don't have to replace anything, except hoses that dry up and crack.

I started using Motul 5.1 on my bikes and I'm in the process of changing everything else  over to it. Unlike Dot 5, it's compatible with DOT 3/4 but has the added bonus that it's not corrosive to automotive finishes.

I would have done it last summer, but my Motul distributor went out of business and I haven't found anyone else that can supply me a 5L can. It's $11/.5L, so buying it in quantity is a must. I'm redoing the brakes n the Spyder and need to flush the 968 and the ML and Smart as well.  

DOT 5.1 has the same negatives as Dot 3 or 4. It will absorb water AND is corrosive to painted surfaces. It is glycol-based, which is why it is compatible with DOT 3 or 4.

Do not make the mistake of putting in 5.1, and then thinking you no longer have to change your brake fluid.

The benefit of 5.1 is that it's boiling point is higher than DOT 3 or 4, and has about an equal boiling point to silicon-based DOT 5.

https://epicbleedsolutions.com...-dot-5-1-brake-fluid

http://www.safebraking.com/wha...dot-5-1-brake-fluid/

Last edited by DannyP

Everyone has the 5.1, in .5L bottles. I have 4 cars and a motorbike to do.  That's why I want a 5L can, which no one has. I'm going to check with one more retailer here in town tomorrow and if they can't order it, I'll throw in the towel and use Ate or Pentosin, both of which are available in 5L cans from Pelican and ECS.

@DannyP posted:

DOT 5.1 has the same negatives as Dot 3 or 4. It will absorb water AND is corrosive to painted surfaces. It is glycol-based, which is why it is compatible with DOT 3 or 4.

Do not make the mistake of putting in 5.1, and then thinking you no longer have to change your brake fluid.

The benefit of 5.1 is that it's boiling point is higher than DOT 3 or 4, and has about an equal boiling point to silicon-based DOT 5.

https://epicbleedsolutions.com...-dot-5-1-brake-fluid

http://www.safebraking.com/wha...dot-5-1-brake-fluid/

I've been using 5.1 in my bikes since ~2005 and I've never had it damage a painted  surface. And with the tiny reservoirs on the handles bars, it's nearly impossible to fill/bleed a system without getting at least a drop on a painted surface no matter how careful you are.

Last edited by dlearl476

I have a Motiv pressurized tank and Gordon made one by himself  My cap did not work out well so I had to gerryRig it but I managed it.  Honestly, it was not a big job and I bought a 1 Liter and an extra 500ml that is left unopened.   I think it is doable at a more consistent pace with this set up.  An extra pair of hands, or feet should you need to pump the pedal,  is really nice to have.

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