bleeding maguras?

water ftw![/QUOTwater is good aslong and it dosint get below 32 degrees where you live. and sorey jc im still going to have to desagree with you on the mineral oil thing

If this applies, add antifreeze. Some trials riders swear by a mix of water, antifreeze, and mineral oil.

Is water more or less compressible that mineral oil (Magura blood or Finish Line Shock Oil)?

I believe water is more compressible, but I’m not sure by how much. Wouldn’t that make water less desirable to use as a brake fluid? Sure, it’s thinner (less viscous) which means the brake pads and brake lever will be more snappy and quick. But when you squeeze the brake lever tight the water would compress more and it might feel a little more spongy.

And would antifreeze be a good thing for the internal seals inside the brake? Might it cause the seals to deteriorate faster?

After ripping my crossover line at CMW, I had to replace line and oil. It was much simpler than I expected it to be.

I tried to find Finish Line 5wt, but none of the LBSs in town carried it (nor did the motorcycle shops). I spoke to a mechanic I trust, who ran HS33s for several years on his bike in the late 90s, and he recommended sewing machine oil as a substitute. It’s very light mineral oil (looks almost like water), and cost less than $2 for something like 6oz.

I had some spare Magura parts and some old tubing from an aquarium’s air pump, and bought a big plastic syringe from my local feed store (a syringe turkey baster would also work fine). I stuck the appropriate fittings on the tubing, then stuck that on the syringe, opened up the bleed port on the brake lever, and pushed the fluid through. I had a second fitting with a tube hooked to the bleed port, and attached that tube to a second bottle to collect the oil again. It took maybe 15 minutes total.

I would recommend reading up a little on the procedure at that execulink site somebody already linked to earlier. The important thing is to back out the TPC and before bleeding, and the guides on that site tell all about how to do that. It’s not a difficult procedure at all, and was actually kind of fun. I figure that, for a cost of maybe $5 out of pocket, I learned how to take care of my brakes, and if it had been a complete disaster, there were always LBSs that would be happy to fix it for me.

yes, no

antifreeze dosent just change the freezing/boiling point of your coolant, it also lubricates the seals in your waterpump.

the rear brake on my bike is pretty solid,the only flex I feel (very minimal) comes from the pads and frame. Since when do liquids ever compress?

sorry but i’m a real noob with hydraulic brakes.

would it work if you got a big tub full of the stuff you are doing, put all the stuff in the liquid, wait for the lquid to fill up into all the neccesary parts, then assemble it all in the liquid?

would that work cause there’s no air that can get in the line?

i assume this would only work with water cause the other stuff is probably expensive and would cost A LOt to do this.

haha, that’s what I do.

Small bubbles can stick to the side of the hose, so I submerge the lever and use the syringe like a plunger to get all those out. foolproof bleed

Liquids do compress due to pressure. Different liquids compress different amounts due to pressure. I don’t know if the pressures in a bicycle hydraulic brake are enough to make a difference.

Here’s some info about water being compressible:

Re: bleeding maguras?

john_childs <>,
quoting []

>> If water got in your brake lines (which is VERY dangerous!) you
>> would notice your pedal would feel sluggish and the brakes wouldn’t
>> work very well, and may not work at all! This is because water
>> compresses much more relative to brake fluid.

This quote is misleading. Actually, water has very low
compressibility, with a volume reduction of 1/3% per 1000 PSI
[]. This is
comparable to hydraulic oil (e.g. mineral oil type brake fluid), which
is somewhat more compressible at 1/2% / 1000 PSI. Glycol- and
silicone-based brake fluids are in the same ballpark, and I vaguely
recall reading that one of these is 1/2 as compressible as the other.

To understand what this means, consider that the brake hose on my
bicycle is rated to 4600 PSI. Water, at this maximum pressure will
lose about 1% of its volume. Of course, the brakes are very
responsive and do not require anything close to max pressure to
securely lock wheel.

The biggest problem with water in a brake system is that the water can
boil at which point it is useless. Other issues I’d worry about are
lubrication and corrosion inside the brake mechanisms.

Hope that helps.


Ah, I thought water was more compressible than that. Seems water would work as a hydraulic brake line fluid for Magura rim brakes. The heat generated by the brake pads is not an issue for the fluid with the rim brakes like it would be for disc brakes.

Thanks for the numbers. I was having a hard time finding that info with Google.