Leaking Maguras

I've had leaking problems in the past. To find where it is, you need to
do the equivalent of submerging a tire to find the leak. Do a bleed on
it so the system is both full and fully-capped (closed system). Then do
a quick surface clean of everything using a cloth with some
grease-breaking detergent (like Dawn). Dry thoroughly. Then pull the
lever to increase the pressure in the system, and look for where the
leak is coming from. Once you know where it's happening, then it's a
different problem-solving exercise to figure out how to fix it. With
any luck it will be a simple part replacement.

There might be better approaches, but that's how I went at it. Key is
to get the oil cleaned off so when you pull the lever you can find out
where the oil is coming from.

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Im sorry I cant be of much help. When my next to new Maguras lost
pressure, I stopped by my LBS and asked them what was up. In my case
there was oil leaking onto the lever. The owner of the bike shop called
up Magura, and they sent a bleed kit and whole new brake lever and top
cylinder setup(dont remember what it is actually called) all without
charge. I paid a few dollars for the bike shop to do the fix.

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I had a case of a leaky Magura that was caused by one of the bolts
actually starting to crack from being overtightened. The head of the
bolt was actually starting to come unattached. Replacing the bolt
fixed the problem.

A rather worrying problem because if the head of the bolt had actually
broken off it would have required some minor surgery to remove the
broken bolt.

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I'm not sure what brake fluid is made of, but it's not oil. There are
several different types, DOT 1, 3, 4 and 5 I think. These aren't
compatible with each other, so you must know what type of fluid to use
before you add any.

I rebuild my motorcycle calipers every few years, as crud and corrosion
makes them stick and leak.

There is a rubber ring around the brake piston that seals in the fluid.
If you get any oil products, like wd40, onto this rubber ring, it will
swell up. The brake will then leak. Be very sure never to get any oil
products near your brakes. There is a special synthetic brake grease
you can buy to lube the pins and piston during assembly.

I don't know why yours are leaking. Rebuilding a caliper is the sort of
thing you want to do every so often anyway.

It's pretty simple, there are few parts. After removing the pads, use
the pressure of the fluid to drive the piston out. If that won't work,
use compressed air. Clean the parts with soap, water, and fine emery
paper. If the rubber parts look new, you can reuse them, although a new
kit isn't usually very expensive.

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The Magura rim brakes use a mineral oil. They do not use DOT brake
fluid. DOT brake fluid is nasty stuff and will mess up paint and do
other nasty things. Some bicycle disc brakes do use DOT brake fluid.

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I followed Tom Blackwood's good advice (thanks, Tom!), and found the
leak on the crossover cable's coupling where it went into the slave
cylinder. I just took it off, cleaned threads etc., reattached, and
then bled it. Seems to be holding up now, but I've ordered a braided
cable set anyway--the plastic hoses really have no flexibility and are
a bit of a pain to work with.

I used standard Magura Blood fluid, but have used sewing machine oil in
the past (my last Craigslist set of HS33s came with a pint of the
official Magura stuff). Many trials riders just use water because it
makes bleeding the system really simple--they submerge the whole thing
in a tub of water, and keep squeezing the lever until all the air's
purged from the system. The risk there, according to some Magura
guru-types, is corrosion.

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I have never seen hydraulic brakes that didn't use some type of brake
fluid, but if John says they use mineral oil, he's usually right.

The point was to be sure, from a manual or site, what type to use. Most
cars and motorcycles will have it stated somewhere on the fill cap.

It's good that you seem to have fixed it. Calipers do benefit from
disassembly and cleaning every few years. I have also seen them messed
up by spraying wd40 on the pistons. If they start to drag, usually it's
the piston sticking a tiny bit.

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maguras use mineral oil, as do some other bike brakes.

I would worry about disassembling the calipers, as the manual says
never to mess with them.

Joe

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Yes magura specifically mention that you should not use DOT fluid, as it
will affect the seals.

The other risk with water is that it will freeze, causing your system
to rupture. Magura reccomend water if you've got no other option, but
suggest that you flush and refill the system with magura blood asap.

--
kington99

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In motorcycles, brake fluid is replaced because it absorbs water from
the atmosphere. So it is changed yearly.

This water in brake fluid is considered super bad on a motorcycle.
Brake friction heat moves from the pads into the calipers. If there is
water there, it will boil, locking the brakes.

Unis, with our super low rpm, and low load, never get that hot I
guess.

I would think that some down hill bikes could boil water. I haven't
worked on any. I have never heard of using water as brake fluid. For
that matter, brake fluid is cheaper then water in many places.

They always say never to rebuild their stuff, buy new stuff. I would
expect any caliper used outside to get gunky and sticky. Trucks seem to
last longer then cars, and motorcycles need work 3x as often as a car.
I would expect tiny bike calipers to need the most work of all. It's
just a piston in a can, sealed with a rubber ring. This pushes against
the brake pad. They are all the same, more or less. Some fancy set ups
will have many pistons etc. Hydraulics is pretty simple.

Car and truck calipers are often a big messy job to clean and
reassemble. The cost of a factory rebuilt item is low.

For old motorcycles, and I will guess bikes, parts for these little
things are costly, compared to car parts. Because the parts are small,
the cleaning and reassembly job is fast and worth doing. Or just buy
new parts. In any event, don't expect calipers to work so great after a
few seasons in the great outdoors. Crud builds up around the pistons
and the brakes start to drag.

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feel the light said:

This water in brake fluid is considered super bad on a motorcycle.
Brake friction heat moves from the pads into the calipers. If there is
water there, it will boil, locking the brakes.

interesting that you say this, coming from the world of car circuit
driving the fear with boiled brakes is that the brakes will be
ineffective as there is gas in the line which is highly compressable.
The effects are most common when returning to the pits, as heat soak
sets in. I've seen guys run in to other cars in the pits at 5mph
because their brakes weren't effective enough to stop them.

I've had mtbing mates who've boiled their brakes with DOT fluid on
serious downhills, the advice to use water always comes from trials
bikers who of course put virtually no heat in to their brakes.

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I have seen many cases of locked brakes on disk trucks, cars and
motorcycles.

The surface between the brake piston and the caliper cylinder collects
dirt, corrosion, dried brake fluid, etc. This makes it want to stick.
Prolonged braking, say an overloaded car going down a mountain, will
boil water in the brake fluid and push the dirty piston out and it gets
stuck.

So it's about dirty brake pistons getting stuck. Anyway, I would buy
new calipers for a car or truck. I could fix them, but it ain't worth
the mess.

I just want to encourage those with older bike disk brakes to consider
that proper disassembly , cleaning and reassembly, is likely to be not
much of a mess, and should restore new performance.

I have never actually worked on any bike disk brakes. 🙂

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