Hydraulic brakes: mineral oil, or brake fluid?

[Nehmo]

Lectric xp 3.0 bought used
The rear brake has no fluid. I suppose there is a leak, but I need to fill that system to find the leak. I've never had hydraulic brakes before, and I was surprised to learn they used mineral oil. Why? Why isn't regular brake fluid (like that for cars) used? Would there be any harm in using regular brake fluid?
This guy used baby oil

with reasonable results.

 

[offGridDownUnder]

The manufacturer picks materials. Those materials work well with some fluids and are damaged by other fluids.

Find out what the manufacturer says to use. Or do what you want and find out later when the brakes fail. Again?

And I wonder what the previous owner used, and whether that caused the leak by damaging the seals? And if it damaged one seal, would it damage all the seals?

 

[scianiac]

Yes only use the fluid type that are designed for, Seth used mineral "baby" oil in mineral oil brakes, so basically he just used thicker than normal mineral oil.

There are some pros and cons to mineral vs brake fluid although honestly I think for the vast majority of users mineral is better. Yes it boils at a slightly lower temp and if I recall also changes properties with temperature slightly more. But unlike DOT3/4 mineral oil doesn't absorb moisture which then lowers the boiling point significantly and makes is corrosive, is considerably more toxic and because it absorbs moisture is also not as shelf stable. Often I've seen DOT brakes where the calibers or levers have their paint or anno corroded off in spots due to fluid spills.

What I don't quite understand is why don't all bike brakes just use DOT5 fluid. Which seems to solve all of these problems, doesn't absorb water, highly temperature stable, high boiling point, very safe, good seal compatibility, doesn't harm most plastics or paints, reasonably widely available, low viscosity. Seems the main reason they don't use it in cars very often is because it can aerate in ABS systems.

 

[Chalo]

Given that glycol based brake fluid has a number of serious drawbacks including toxicity and the ability to damage many materials used in bicycles, but without having any advantages in the bicycle application, I think it's wise to reject any bicycle brakes that are designed for DOT fluid. Mineral oil hydraulic brakes are stupid and unnecessary enough; there's no need to stack up stupid and unnecessary features.

It's just more moto-fetishism, where "what's best for my atrocious pickup truck/F1 cars/helicopters must be best for my bike". In other words, infantile bozo thinking.

 

[Hillhater]

Interesting topic..but sshould be posted/moved to the “Technical” section.

 

[lnanek]

> Mineral oil hydraulic brakes are stupid and unnecessary enough

Maybe it's just because I only tried the cheap ones that came with my ebike, and read about cheap Avid ones where only one side moves, but I find mechanical disc brakes to be weak, noisy, finicky to adjust, and finicky to keep adjusted.

Give me cable actuated mineral oil hydraulic any day. I'm fine with non-hydraulic caliper rim brakes too, though. Hate adjusting the springs on v-brakes even with expensive levers with return springs and adjustable pivots and throw. Anything with springs I have a high chance of accidentally bending too much and never getting it back to working strongly enough.

I've turned down every full hydraulic bike I've been offered, but just because my first step is always to move the bars and I don't want to bother redoing hydraulic brake lines. I admit I've had to learn how to bleed my cable actuated hydraulics anyway and have a kit for it, though. So I definitely pay a cost in increased maintenance over purely mechanical.

 

[Chalo]

Give me cable actuated mineral oil hydraulic any day.

Ah, the worst of everything. Cable friction and squishiness, plus oil to leak and destroy the pads instantly. Plus, putting all the heat and all the oil right in the same place. Brilliant.

My first disc brakes were Mountain Cycle Pro Stop cable-hydraulics. They sucked even though they were friggin huge and fussy to set up. But I never rode them long enough to make them leak and annihilate their own pads, at least.

 

[offGridDownUnder]

I've switched the motor on my trike to the intended Grin All-Axle v3 rear now, and on my reference hill (measured at 12% by my iPhone app) it will slow the trike and me to a crawl downhill. I'll get into tuning the parameters and see what I can achieve, but that's good enough.

This is an electric bicycle forum, and I think the best brakes are regen brakes, backed by cable brakes for no-fuss reliability for emergencies.

Remember also there is a brake in your brain - the one that operates on the "don't ride like an idiot" principle. Judicious application of this one pays off on all fronts.

 

[Chalo]

This is an electric bicycle forum, and I think the best brakes are regen brakes,

Those aren't brakes, and they don't work as well as real brakes. It's a little like driving a standard transmission and claiming that engine drag is the best brakes. I mean, sure... but you're very wrong.

Reversing torque through a flatted axle, as with 99+ percent of direct drive hubs, is a great way to introduce very expensive show-stopping unreliability to your bike. All to save a nickel's worth of juice if you're lucky. It's nonsense bordering on the pathological.

 

[lnanek]

Flatted axle complaint doesn't apply to all axle, it has a built in torque arm. Amount of juice recovered is worthless, but some heavy users benefit from not having to replace pads every four months.

 

[gromike]

Amount of juice recovered is worthless,

but seeing on the display several hundred of negative watts is priceless.

 

[offGridDownUnder]

a flatted axle

The nonsense is using a motor with a flatted axle, just because someone was too cheap to manufacture a proper motor.

Caveat emptor. Just because a supplier is cheap or dumb, that doesn't mean I have to be cheap or dumb.

 

[offGridDownUnder]

Those aren't brakes, and they don't work as well as real brakes.

I did clearly write that I have my regular brakes as backup, so no, I'm not very wrong.

 

[wturber]

Those aren't brakes, and they don't work as well as real brakes. It's a little like driving a standard transmission and claiming that engine drag is the best brakes. I mean, sure... but you're very wrong.

Reversing torque through a flatted axle, as with 99+ percent of direct drive hubs, is a great way to introduce very expensive show-stopping unreliability to your bike. All to save a nickel's worth of juice if you're lucky. It's nonsense bordering on the pathological.

I dunno. I ran two torque arms and made sure the rear axle's nuts were tightened properly. Worked fine. Saving money on electric power is hardly a major point for regen braking. Reducing brake maintenance (time and expense) and maybe extending range a bit in some situations are the main benefits. I was quite happy with enabling even the relatively crude regen from my KT controller. It was a nice additional brake and worth having in my experience. I miss having it on my current cargo bike.

 

[marty]

If baby oil is good for brakes. Then brake fluid must be good for babies! Just wiped my new born little baby girl with some DOT 3 Brake Fluid and she loves it Smells a little funky

Olive oil is made by squeezing olives till the oil comes out. Therefore, Baby Oil is made by squeezing babies till the oil comes out. That is why baby oil smells like babies.