Hydraulic Brake Fluids (A Relaxed Talk)

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
As many of you already know, manufacturers of hydraulic bike brakes are divided into ones that use proprietary mineral oil (Shimano, Magura, Tektro/TRP...) or DOT (glycol based fluid) -- and that would be SRAM -- for their system. It is not worthwhile to discuss pros and cons of both systems, as such information can be readily found in numerous online articles. Suffice to say, mineral oil is less effective than glycol at temperatures below the freezing point while glycol based fluid could potentially boil on long descents when the brakes are hot. Another point is, DOT fluid composition and properties are perfectly known while no one except the manufacturer knows anything about the proprietary mineral oil of given brand. Finally: you cannot replace mineral oil with DOT and vice versa.

My brother has done quite a research about automotive brake fluids. He has found mineral oil was used for cars by 1970s, and Citroen was making car braking systems based on mineral oil by 1982. (Afterwards, DOT fluids totally replaced the mineral oil for cars). Nowadays -- he says -- all agricultural machinery including tractors use mineral oil for hydraulic brakes. The only information given for such mineral oil brake fluid is its pour point (and viscosity at different temperatures). And, the fact all such fluids contain ZDDP (Zinc Dialkyldithiophosphate) as an additive is widely known.

As he was indeed irritated with poor performance of Shimano brakes at recent low temps, he did test Febi Bilstein 06162 (power steering fluid); he put a bag of such oil with pour point of -40 C (-40F) into the freezer to find the apparent viscosity didn't change very much from the room temperature down to -12 C (the cold fluid behaved as it were water). Encouraged, he replaced dirty oil in his 4-piston Shimano disk brakes with that mineral oil.

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The transfusion :)

He reports his brakes act normally after the oil replacement. Now, we are waiting for severe frosts again to test the performance of his brakes in real life.

I have not written the above to encourage anybody to experiment with their hydraulic brake fluid. I'm just curious... Given neither Shimano nor Magura nor Tektro/TRP publish any data about their mineral oil brake fluids, is that possible each of those brands found their single source for relatively cheap mineral oil, and just pour such oil into small bottles, and charge a lot for the proprietary mineral oil?
 
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PDoz

Well-Known Member
Stefan, I have zero experience in cold temperatures, but my recollection is the issue with mineral based hydraulic systems in cold is related to their BENEFIT - mineral brake fluid is hydrophobic , so water in the system separates out and then collects around the calipers ( lowest point) - causing stiction at the seals. I suspect your brother has flushed out that water when bleeding the brakes?

Personally, I prefer shimanos mineral system. But that's because of years of DOT fluid sucking up water then having brakes fail at the worst possible moment.....I have way too many cooked brake stories from decades of doing silly things on motorbikes. Plus an extremely frustrating to bleed set of sram brakes on my levo sl.
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
This is not exactly so, PDoz. True, glycols are hygroscopic. However, any moisture that might enter the hydraulic lines gets totally dissolved in glycol, and glycol-water mixtures have extremely low freezing point (that's why DOT fluids are commonly used in automotive brakes). With mineral oil -- as you said -- water separates out and collects near the calipers. With low temperatures, pistons just freeze, and the brakes cease to work. (We heard from @Prairie Dog about mysterious brake blocking at very low ride temperature). Another phenomenon is increased viscosity of mineral oil in low temps, causing delays on braking.

Of course my brother flushed and bled the hydraulic lines; it was actually him who told me about freezing the pistons because of the presence of free water in the system, and about the delay in braking due to higher oil viscosity.

On the other hand, you know very well what happens at the opposite end of the temperature spectrum, when the brakes are hot because of violent and/or prolonged braking in the mountains. Some DOT fluids boil pretty easily. If glycol has absorbed water, the boiling temperature becomes pretty low. Not sure whether free water in mineral oil system could boil as well, making the brakes ineffective?
 
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PDoz

Well-Known Member
This is not exactly so, PDoz. True, glycols are hygroscopic. However, any moisture that might enter the hydraulic lines gets totally dissolved in glycol, and glycol-water mixtures have extremely low freezing point (that's why DOT fluids are commonly used in automotive brakes). With mineral oil -- as you said -- water separates out and collects near the calipers. With low temperatures, pistons just freeze, and the brakes cease to work. (We heard from @Prairie Dog about mysterious brake blocking at very low ride temperature). Another phenomenon is increased viscosity of mineral oil in low temps, causing delays on braking.

Of course my brother flushed and bled the hydraulic lines; it was actually him who told me about freezing the pistons because of the presence of free water in the system, and about the delay in braking due to higher oil viscosity.

On the other hand, you know very well what happens at the opposite end of the temperature spectrum, when the brakes are hot because of violent and/or prolonged braking in the mountains. Some DOT fluids boil pretty easily. If glycol has absorbed water, the boiling temperature becomes pretty low. Not sure whether free water in mineral oil system could boil as well, making the brakes ineffective?

Can you explain what us different about what you just wrote and what I was describing?

Water that comes out of mineral systems freezes the calipers.
Water in dot fluid allows it to boil easier halfway down heart attack hill....
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
Can you explain what us different about what you just wrote and what I was describing?

Water that comes out of mineral systems freezes the calipers.
Water in dot fluid allows it to boil easier halfway down heart attack hill....
The main difference is the DOT system causes no issues during the frost.
I do not know if free water in mineral oil might boil during a downhill ride.

If there has been any misunderstanding from my side, please attribute that to my poor command of Australian :)
 

sc00ter

Active Member
My E-Lux brakes were acting weird and I mentioned it to a friend at work. He races mountain bikes and does all his own service work. He offered to bleed the brakes and check the rotor torque for a lunch. It was very involved, much more than a motorcycle. He had the equipment and fluids but I did as much as possible under his guidance. Brakes worked perfect afterwards. I not only bought him lunch but grabbed him a six pack of beer as well. You always hear people complain about the labor rates at bicycle shops, but modern bicycles are so technical now.
 

Marcela

Well-Known Member
Way back I had a british MG Midget car. It required a type of brake fluid that was compatible with the seals, whatever that was. I mistakingly used regular dot 3 brake fluid, the seals swelled up and had all sorts of trouble. One being the brakes froze up and the rotors were glowing red.

Be careful what ye mix and match.
 

PedalUma

Well-Known Member
Region
USA
I highly suspect that the proprietary fluids are just small bottles with generic stuff from a rail tanker with dye added, exactly as suggested by Stefan. I wish that there was a brake system for bikes that used DOT 5. Or if systems were sold dry so that we could use DOT5 from day one. DOT 5 is used in antique cars because it is chemically inert. Sitting for years will not effect it. It won't even damage paint. It has a boiling point of 260C and it cannot absorb moisture.
How much would you need to flush a system to use it instead of mineral oil? It cannot hurt anything because it is inert.
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
The pros and cons of DOT 5 are exactly same as of mineral oil. Additionally, DOT 5 will absorb air, which is not a good thing.
 

Marcela

Well-Known Member
Wonder how sewing machine oil would work, which I think is something like 10w mineral oil without any additives. Or something synthetic like 0w non detergent would be pretty thin. Hydraulic fluid is pretty thin.
 

PedalUma

Well-Known Member
Region
USA
Getting air out of the brake fluid such a DOT 5.1 before using it by keeping in a vacuum is an ordeal. It will bubble like sparkling wine for an hour while dissolved gasses are released.
 

Prairie Dog

Well-Known Member
Region
Canada
City
Red Deer
We heard from @Prairie Dog about mysterious brake blocking at very low ride temperature). Another phenomenon is increased viscosity of mineral oil in low temps, causing delays on braking.
My cold clime experience with Shimano brakes on the Trance could only be described as at below normal operating parameters, -30C to be exact. Lever action on both brakes was noticeably stiffer and I would contribute that to the oil in the lines becoming more viscous, water collecting at the calipers or both. Brakes were also squealing quite loudly albeit only during sudden stops. I’ve had the bike out before at -20C with no visible side effects.

Mineral oil may have less viscosity stability than DOT but at that low a temperature I can’t say if there would have been any significant improvement with a glycol brake fluid. With that said, I’ve been told that mineral oil-based systems from Shimano also use a different piston material in their seals and that its elastomer properties tend to change under extreme cold which I can only assume happened in my situation. Once the bike was brought inside the house, I noticed slight weeping around the rear brake lever pivot post several hours later. I suspect some fluid managed to escape past the compromised seals as a result of the cold conditions. There was also a significant loss of pull tension on the rear brake lever which I attribute to air being present in the line. The front brakes were fine. A full bleed on the rear brakes appears to have resolved the issue and there’s no further sign of visible oil seeping at the lever. The same brake was recently bled five months ago.

From now on, I intend to be more selective with respect to the days that I ride or simply resume riding my standard reliable rigid with its mechanical cable actuated brakes on extremely cold days. FWIW, we hit a low of -29C this morning and it appears that the cold will be here to stay at least until the weekend.

Stefan, I look forward to Jacek’s further cold weather testing using the mineral oil-based PSF. I’ve also heard that Castrol and Citroen offer low temp (mineral oil) fluids as well.
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
My cold clime experience with Shimano brakes on the Trance could only be described as at below normal operating parameters, -30C to be exact. Lever action on both brakes was noticeably stiffer and I would contribute that to the oil in the lines becoming more viscous, water collecting at the calipers or both. Brakes were also squealing quite loudly albeit only during sudden stops. I’ve had the bike out before at -20C with no visible side effects.

Mineral oil may have less viscosity stability than DOT but at that low a temperature I can’t say if there would have been any significant improvement with a glycol brake fluid. With that said, I’ve been told that mineral oil-based systems from Shimano also use a different piston material in their seals and that its elastomer properties tend to change under extreme cold which I can only assume happened in my situation. Once the bike was brought inside the house, I noticed slight weeping around the rear brake lever pivot post several hours later. I suspect some fluid managed to escape past the compromised seals as a result of the cold conditions. There was also a significant loss of pull tension on the rear brake lever which I attribute to air being present in the line. The front brakes were fine. A full bleed on the rear brakes appears to have resolved the issue and there’s no further sign of visible oil seeping at the lever. The same brake was recently bled five months ago.

From now on, I intend to be more selective with respect to the days that I ride or simply resume riding my standard reliable rigid with its mechanical cable actuated brakes on extremely cold days. FWIW, we hit a low of -29C this morning and it appears that the cold will be here to stay at least until the weekend.
You analysis has been the most interesting!
I’ve also heard that Castrol and Citroen offer low temp (mineral oil) fluids as well.
That is correct.
 

Cowlitz

Well-Known Member
Please send your brother to my house.

I have been unable to test my brakes because the roads are very slick around here. We may get above freezing this weekend? Or not. As far as bike shops being expensive, I don't think that the one that I go to is. I do have to drive a bit to get there, and then have coffee and a pastry while waiting, and maybe go into the book store and buy a book, so maybe it is expensive?
 

Neeko DeVinchi

Active Member
Region
United Kingdom
Just out of curiosity but can anyone tell me whether it is truly beneficial to use the Royal Blood mineral oil with Magura brakes instead of traditional shimano mineral oil.

Yes, yes. I'm aware that they are different in terms of viscosity. But I've usually used shimano mineral oil for all of my mineral oil brakes.

My pistons have never seized. No leaks around the banjo or olive. The odd air build up but a simple brake burp sorts it.

Apologies if my post exceeds the threads relaxed vibe. I'm just enthusiastic 😅
 

Stefan Mikes

Well-Known Member
Region
Europe
City
Brwinów (PL)
Why You Should Not Improve Your Brakes During The Winter :D

I had a peek at the Strava activity feed to see my brother Jacek had had a 67 km Warsaw ride on the Epiphany (we call it Three Kings Day in Poland), and there was something alarming in his post. The ride description: "Some adventures. That's why you shouldn't improve your brakes during the Winter". Next, a picture of his Garmin in the Crash Mode. Next, a photo of his broken mirror on the bike path. And, a nice photo of the Warsaw Mermaid.

I was sure he lost his brakes because of using the synthetic oil in the hydraulic brake lines of his Giant Trance E+! I messaged Jacek instantly:
-- What's happened to you, bro?
-- Nothing serious. Broken rear-view mirror, a bruised elbow... And Garmin took it for a crash! Certainly, the crash sensor in the Edge works!
-- Did you lose your brakes?!
-- On contrary. They were too effective. I was taking a U-turn to take a pic of the Mermaid, accidentally hit the brake lever, the front wheel stopped me and I was on the ground! After my brake service, these 203 mm rotors are damn effective!

Meaning, he did the brake servicing properly, the synthetic oil as brake fluid turned out to be excellent, only Jacek did the same mistake as I used to do in the past on the same e-bike... (at least two hard crashes because of stopping the Trance too hard at low speed).

1641500187665.png

Jacek's son got notified his Dad had had a crash.

1641500279808.png

The glass in Mirrycles never breaks. It is the mirror arm that breaks.

1641500428776.png

The Warsaw Mermaid (the best known of all Mermaid statues of Warsaw). Brother took the picture anyway.

1641500524519.png

On his way home, mirrorless.
 
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Cowlitz

Well-Known Member
Why You Should Not Improve Your Brakes During The Winter :D

I had a peek at the Strava activity feed to see my brother Jacek had had a 67 km Warsaw ride on the Epiphany (we call it Three Kings Day in Poland), and there was something alarming in his post. The ride description: "Some adventures. That's why you shouldn't improve your brakes during the Winter". Next, a picture of his Garmin in the Crash Mode. Next, a photo of his broken mirror on the bike path. And, a nice photo of the Warsaw Mermaid.

I was sure he lost his brakes because of using the synthetic oil in the hydraulic brake lines of his Giant Trance E+! I messaged Jacek instantly:
-- What's happened to you, bro?
-- Nothing serious. Broken rear-view mirror, a bruised elbow... And Garmin took it for a crash! Certainly, the crash sensor in the Edge works!
-- Did you lose your brakes?!
-- On contrary. They were too effective. I was taking a U-turn to take a pic of the Mermaid, accidentally hit the brake lever, the front wheel stopped me and I was on the ground! After my brake service, these 203 mm rotors are damn effective!

Meaning, he did the brake servicing properly, the synthetic oil as brake fluid turned out to be excellent, only Jacek did the same mistake as I used to do in the past on the same e-bike... (at least two hard crashes because of stopping the Trance too hard at low speed).

View attachment 111159
Jacek's son got notified his Dad had had a crash.

View attachment 111160
The glass in Mirrycles never breaks. It is the mirror arm that brakes.

View attachment 111161
The Warsaw Mermaid (the best known of all Mermaid statues of Warsaw). Brother took the picture anyway.

View attachment 111162
On his way home, mirrorless.
That's a very scary mermaid.