Is there a reason why brakes designed for dot fluid can’t be used with mineral oil instead? I understand why it won’t work the other way round given how corrosive dot fluid is but given that mineral oil isn’t harmful, what would be the issue? I ask because I fancy trying sram road levers with different callipers.I know Hope mentioned producing some but have heard nothing since and it would be easier if cheap shimano ones worked. Also, if Hope were going to do after-market callipers, it would seem to be simpler to make one if they could rather than a variety.

Posted 5 years ago

It will swell and ruin the seals.

Hope make two different road calipers because of this.

Well, that and piston ratios. Either way, the two fluids are not interchangeable either way around.

Posted 5 years ago

Mineral oil is oil like alkanes

DoT fluid is a mix of synthetic compounds like glycol ethers.

So no you can’t interchange them.

Posted 5 years ago

Yeh it’s the seals that are incompatible. Made of different material to work with the different types of oil to stop swelling etc.

Ratios have nothing to do with it, a hydraulic ratio doesn’t change when you change the fluid, it’s created by the difference in piston diameter.

Posted 5 years ago

Are the hope ones available yet?

Posted 5 years ago

As mentioned above, the Hope callipers for Sram and Shimano are different, different seals and different piston sizes and volumes. The calliper has to work with the reservoir volume.

Posted 5 years ago

Thanks for the answers.I thought there must be a reason though it would not appear to be beyond the wit of man to make different rubber seals for the same calliper. As for piston sizes, if they were similar diameters I would have thought they would behave similarly.

Posted 5 years ago

Similar piston sizes will behave similarly. The same piston sizes with behave the same.

However, it can be a fine line between working and not working.

The Hope road calipers come in two types because of seals AND pistons. Otherwise, they’d only make one caliper and fit different seals.

Ratios have nothing to do with it, a hydraulic ratio doesn’t change when you change the fluid, it’s created by the difference in piston diameter.

Thanks!

Posted 5 years ago

I’m sure you could make different seals to allow the different oils to be used in the same calipers.

Problem would be inability to tell what you had and ensuing warranty and injury claims when brake seals started failing due to oil mix. Physical exterior difference makes it easy to tell even if company uses same internal with different seals…

Posted 5 years ago

Erm, do SRAM and Shimano use different fluid?

Posted 5 years ago

Yes, shimano is proprietary mineral oil, sram is DOT fluid.

Also, despite the comments above, both road calipers push different amount of fluid, enough to justify producing two different calipers.

I asked how they got around the fluid difference when they first released these. The answer was, they didn’t, they had to produce 2 version but as they pushed different volumes of fluid, they had to anyway.

Posted 5 years ago

Erm, do SRAM and Shimano use different fluid?

yes.

Posted 5 years ago

Are the hope ones available yet?

Yes

Posted 5 years ago

Erm, do SRAM and Shimano use different fluid?

yes.[/quote]
Well I’d better remember that. Thanks.

Posted 5 years ago

Slight thread drift:is there any technical reason for different brakes using different fluids? Or is it just brand preference?

Posted 5 years ago

This is a good read…

http://www.epicbleedsolutions.com/blog/dot-brake-fluid-vs-mineral-oil/

Posted 5 years ago

Primarily higher boiling point in DOT 5.1, less brake fade (in theory). Less compressible so less spongy (in theory, so long as well bled).

Noting that DOT 5 is a different thing and you should never put DOT 5 in DOT 5.1 brakes (4 is okay though, but has a lower boiling point).

DOT glycol based stuff are hygroscopic so absorbs water from air moisture which can mess it up.

Posted 5 years ago

Viscosity

Tech Speak: Brake Fluid Break Down & Implications for Road Disc

Posted 5 years ago

Mineral oil is more stable and non corrosive – but goes thick in the cold.

Its interesting that Shimano and Citroen are the only folk I know who use mineral oil and citroen have to as its all part of a hydraulic system

Posted 5 years ago

Its interesting that Shimano and Citroen are the only folk I know who use mineral oil and citroen have to as its all part of a hydraulic system

Errm and Magura and Clarks and Tectro…

Posted 5 years ago

Post 1980 Rolls Royce also use Mineral oil 8)

Rolls Royce Brake Fluid

Posted 5 years ago