Which Brakes? Avid Mechanical Disc? Magura Big or Marta HydraulicDisc?

"coyoteboy" wrote in message
...
Paul Boyd wrote:
(can you even still get open systems?), and they just keep

Lots of the top end systems are open - its how they get automatic pad wear
adjustment. Certainly most of the systems I've seen on the trail have been
open - closed just makes no sense - need to adjust pad on the fly and back
it off if you heat the caliper up.

Indeed. If you get your brakes hot, closed doesn't work. And I got that on
hardly any hill at all. But then this was on a tandem.

working. They may need to be bled once every so often, but cables need
maintenance more than once every so often. All brakes need pads/blocks
replaced periodically, so I'm genuinely interested in why you think discs
aren't "fit and forget".

And if you want to bleed them, which isnt really needed for a decade at a
time, you just lob a piece of hose on the nipple, take the top off the
caliper and squeeze, undo, tighten, release a few times and its done - not
even as complex as replacing a cable!

Hmm. I'm guessing you've never bled a set of Hopes then. I've done one end
of ours, and it was a right pain, even with the bleeding kit.

One problem is them using DOT brake fluid. I _hate_ DOT brake fluid. (My car
doesn't use it either...). It needs changing in a way that the mineral oil
doesn't - 2 years, not 10.

I guess if I had Magura disks, some of my complaints may go away. (Shimano's
a no-no based on the use we give them).

The reason I say the discs aren't fit and forget in the same way as the
magura rims is that I have had to do this sort of crap on them, whereas the
rims have been sealed since I fitted them 10 years ago, and have never given
any problems.

There is another question though : is it worth the hassle? And the answer
for the MTB tandem is definitely yes. Can't tell for the road tandem since
nobody makes suitable hydraulic discs...

(Paul - does this answer your question too?)

cheers,
clive

On 29/08/2007 19:58, coyoteboy said,

Lots of the top end systems are open - its how they get automatic pad
wear adjustment. Certainly most of the systems I've seen on the trail
have been open - closed just makes no sense - need to adjust pad on the
fly and back it off if you heat the caliper up.

OK - I didn't realise the first bit, but the second bit? That's why
Shimano have the bladder in the lever - so that as the fluid expands the
air in the bladder compresses to compensate. Perhaps I'm
misunderstanding what is meant by a closed system.

And if you want to bleed them, which isnt really needed for a decade at
a time, you just lob a piece of hose on the nipple, take the top off the
caliper and squeeze, undo, tighten, release a few times and its done -
not even as complex as replacing a cable!

Surely that's the same for any system, except I assume you mean take the
top off the lever?

--
Paul Boyd
http://www.paul-boyd.co.uk/

"coyoteboy" wrote in message
...

Many disc manufacturers use mineral oil like maggies so it doesnt absorb
water, but even so the DOT based fluids never reach the sort of heat
required to "wet boil" in anything other than extreme downhill conditions.

Remember I'm using ours on a tandem...

I just dont understand where this idea that hydro discs are "high
maintenance" comes from.

I'm not sure where you get it from either. I'm talking about relative to the
rim brakes.

But if you consider this experience -

Rim brakes : Worked out of the box, zero maintenance required of the
internals in 10 years

Discs : Need bedding in, needed bleeding to make the back brake work,
pistons misbehaving a little in 2 years. And of course there's the way the
disc pads can't cope with oil on them :-( (got sintered now, so you just
need to let the smoke out to fix this - but the rims don't suffer in this
way)

them you might understand where I'm coming from.

cheers,
clive

Paul Boyd wrote:
(can you even still get open systems?), and they just keep

Lots of the top end systems are open - its how they get automatic pad
wear adjustment. Certainly most of the systems I've seen on the trail
have been open - closed just makes no sense - need to adjust pad on the
fly and back it off if you heat the caliper up.

working. They may need to be bled once every so often, but cables need
maintenance more than once every so often. All brakes need pads/blocks
replaced periodically, so I'm genuinely interested in why you think
discs aren't "fit and forget".

And if you want to bleed them, which isnt really needed for a decade at
a time, you just lob a piece of hose on the nipple, take the top off the
caliper and squeeze, undo, tighten, release a few times and its done -
not even as complex as replacing a cable!

On 29 Aug, 19:19, Paul Boyd wrote:
On 29/08/2007 19:58, coyoteboy said,
OK - I didn't realise the first bit, but the second bit? That's why
Shimano have the bladder in the lever - so that as the fluid expands the
air in the bladder compresses to compensate. Perhaps I'm
misunderstanding what is meant by a closed system.

Yup, i think thats where the confusion comes in - a closed system is
one where the entire volume of the fluid is under pressure when the
lever is squozed An open system has a reservoir (be it a bladder or
a cup etc). A closed system is like the magura HS33 - there is no
reservoir meaning if the system heats enough to make the fluid expand
you have to back off either the lever position or a separate adjuster
(just another piston essentially) to stop the brakes binding. The open
system relies on seal flex to pull the pistons back and pushes spare
fluid back into the reservoir, but as the fluid heats up it gets
pushed back into the reservoir naturally and doesnt affect the piston
position.

Surely that's the same for any system, except I assume you mean take the
top off the lever?

Yes, it is for any hydro system (I wasnt disagreeing with your post, I
was confirming). Maggies (HS33) are harder than most to bleed when
needed due to the fact that they are closed and you need to remove
every last bubble from the lever to prevent spongeyness - this was the
main problem I had brought back to me time and time again by HS33
owners who had had a go at bleeding.

J

Clive George wrote:

That isn't "forgotten about them". I've never opened the rim brake
internals - and they are 10 years old now.

I've replaced the magura blood after 4 years (just because I got some
for free) and it makes definite difference to pad movement feel. But
then my other HS33s had their oil replaced with chip oil when i ripped
the hose out of them on holiday and that works just as well to this day.
I think the point is that there is no need to bleed a disc, as there
isnt with a HS33. Many disc manufacturers use mineral oil like maggies
so it doesnt absorb water, but even so the DOT based fluids never reach
the sort of heat required to "wet boil" in anything other than extreme
downhill conditions. People often bleed hydro discs because they assume
they "should" - there is no need.

All brakes need pads/blocks replaced periodically, so I'm genuinely
interested in why you think discs aren't "fit and forget".

Compared to the magura rim brakes, they aren't IME. That's it.

IME (I "maintain" 2 sets of HS33s - one pair of Raceline D and one
newer, 2 hope DH4s, 1 hope mini, 1 hope mini mono, a pair of louise FRs
and have direct contact with owners of cheapo cable and shimano XT discs
and have plain old Vs on the old machine that gets no use these days)
they are comparable to maggies - in fact less effort required, and less
problems with rim damage effecting them. The worst thing is the
occasional bouts of squeel, but then the HS33s get that with the wet
weather pads from time to time too. I managed to melt a set of HS33 pads
to the rim in the alps (DH course) and have blue'd the rotors on the
DH4s and mini several times. I just dont understand where this idea that
hydro discs are "high maintenance" comes from. I'd not replace my
maguras on my trials bike because the discs just dont bite as
aggressively at low speed, but then the maggies dont control as well at
high speed so I wouldnt use them on my MTB anymore - even with the
maggies I've run into the back of my brother (DH4s) on numerous
occasions due to the poorer high-speed braking (which is still
blisteringly good IMO).

On 29 Aug, 19:13, "Clive George" wrote:
"coyoteboy" wrote in message
Indeed. If you get your brakes hot, closed doesn't work. And I got that on
hardly any hill at all. But then this was on a tandem.

Tandems are a tad of an issue being essentially twice the energy being
dissipated as the brake was designed for. Must say I've never worked
on them but I cant see any reason why the mechanics of the work is any
different.

Hmm. I'm guessing you've never bled a set of Hopes then. I've done one end
of ours, and it was a right pain, even with the bleeding kit.

Yup, hopes were my first ever disc, never had a problem, never had the
bleed kit. I've shortened hoses on them a few times between frame/fork
changes on other peoples bikes and I didnt find bleeding them an issue
at all? Certainly easier than magura HS33s. But then I'm used to
bleeding the brakes on my car - maybe that helps? I didnt think it
could possibly be considered a difficult task?

One problem is them using DOT brake fluid. I _hate_ DOT brake fluid. (My car
doesn't use it either...). It needs changing in a way that the mineral oil
doesn't - 2 years, not 10.

No it doesnt - this is where you are mistaken. It requires changing
only if you are going to overheat it - recommendations of 2 years are
set by car standards (which were thought up decades ago when brake
systems were considerably more agricultural and allowed moisture
absorbtion easily) and our brakes do not reach the heat of a car
caliper (though, of course, a tandem may get closer). Even on a DH run
in the alps myDH4 /calipers/ rarely got hot enough to burn with me
(15stone, the bike at 40lbs and speeds of 40mph). The wet boil temp of
DOT4 is 155 degrees C - if you get your calipers to anywhere near 155C
i bow down to your superior braking! (or pass you on the way down :-),
most braking is un-necessary if you pick the right lines) I've yet to
hear of anyone boiling fluid in a bike brake - fading organic pads due
to outgassing, yes (solved by choosing a correct pad material from the
start). On a car - yes. The primary reason for bleeding DOT fluids is
to remove the fluid which has absorbed water (hence the wet boil
temps) and return "dry" fluid which boils at 240C. I actually change
out my fluid for DOT5.1 if I change the cable routing etc and have to
bleed, much the same as I'd change the cables on a cable brake or
change the fluid on the maggies.

I guess if I had Magura disks, some of my complaints may go away. (Shimano's
a no-no based on the use we give them).

Yes, I agree you wouldnt want shimano discs on a tandem - too
lightweight IME.

The reason I say the discs aren't fit and forget in the same way as the
magura rims is that I have had to do this sort of crap on them, whereas the
rims have been sealed since I fitted them 10 years ago, and have never given
any problems.

Why did you have to bleed it? It just isnt necessary. And as
mentioned, it couldnt be an easier task to blow through new fluid, not
like when you get really bad bubbles in and have to get shut of them
too. I'll do a youtube vid soon, maybe I have some magic technique I
didnt know was magic?

There is another question though : is it worth the hassle? And the answer
for the MTB tandem is definitely yes. Can't tell for the road tandem since
nobody makes suitable hydraulic discs...

I'm missing where the hassle comes in TBH - which was my point from
the start - hydros are the most fit and forget items on any bike I've
owned or maintained!

On 29/08/2007 20:12, CoyoteBoy said,

Yup, i think thats where the confusion comes in - a closed system is
one where the entire volume of the fluid is under pressure when the
lever is squozed An open system has a reservoir (be it a bladder or
a cup etc).

I was totally confused, wasn't I? :-)

--
Paul Boyd
http://www.paul-boyd.co.uk/

On 29 Aug, 19:24, "Clive George" wrote:
"coyoteboy" wrote in message

...

Many disc manufacturers use mineral oil like maggies so it doesnt absorb
water, but even so the DOT based fluids never reach the sort of heat
required to "wet boil" in anything other than extreme downhill conditions.

Remember I'm using ours on a tandem...

I just dont understand where this idea that hydro discs are "high
maintenance" comes from.

I'm not sure where you get it from either. I'm talking about relative to the
rim brakes.

You are suggesting that hydro discs need frequent maintenance and are
more complex than the rims - im suggesting they arent.

But if you consider this experience -

Rim brakes : Worked out of the box, zero maintenance required of the
internals in 10 years

Discs : Need bedding in, needed bleeding to make the back brake work,
pistons misbehaving a little in 2 years. And of course there's the way the
disc pads can't cope with oil on them :-( (got sintered now, so you just
need to let the smoke out to fix this - but the rims don't suffer in this
way)

It takes a short ride to bed a disc - 10-20 miles - if it takes longer
you have the caliper mis-aligned. Maggies also need you to carefully
align the pads or you get squeeks and the pads wearing unevenly. Why
would you have to bleed the rear? Presumably to fit to the frame- the
same with any hydro brake such as HS33? Why (and how) are the pistons
misbehaving - this again suggests you have the caliper misaligned to
start with - the pads pushing at odd angles tend to get jammed and not
retract well? This is totally contrary to my experience with well set
up discs, but i did get to practice on a few customers bikes before I
could afford my own! No, pads cant cope with oil on them, but then
maggie pads cant cope well in mud and ice. If you get oil on them then
thats carelessness, not the brake at fault - at least when out on the
trail a disc will work when drowned in mud and ice (better in most
cases) while maggies tend to tail off a little, especially at speed
again. If you ride in any real snow you'll find maggies get a nice
smooth layer of snow-ice packed onto the rim eventually - this isnt
fun - discs remain hot and prevent this.

"CoyoteBoy" wrote in message
oups.com...
On 29 Aug, 19:13, "Clive George" wrote:
"coyoteboy" wrote in message
Indeed. If you get your brakes hot, closed doesn't work. And I got that
on
hardly any hill at all. But then this was on a tandem.

Tandems are a tad of an issue being essentially twice the energy being
dissipated as the brake was designed for. Must say I've never worked
on them but I cant see any reason why the mechanics of the work is any
different.

No, the mechanics are the same.

Hmm. I'm guessing you've never bled a set of Hopes then. I've done one
end
of ours, and it was a right pain, even with the bleeding kit.

Yup, hopes were my first ever disc, never had a problem, never had the
bleed kit. I've shortened hoses on them a few times between frame/fork
changes on other peoples bikes and I didnt find bleeding them an issue
at all? Certainly easier than magura HS33s. But then I'm used to
bleeding the brakes on my car - maybe that helps? I didnt think it
could possibly be considered a difficult task?

Maybe the mono levers are more of a pain then. Certainly the bits which are
similar to a car were no problem whatsoever - but the reserviour is
significantly more hassle, being all tiny and fiddly and having no spare
capacity.

One problem is them using DOT brake fluid. I _hate_ DOT brake fluid. (My
car
doesn't use it either...). It needs changing in a way that the mineral
oil
doesn't - 2 years, not 10.

No it doesnt - this is where you are mistaken. It requires changing
only if you are going to overheat it

Or if it gets wet. The mineral oil I have sitting around won't suffer this -
but the container of DOT fluid may well do :-(

The wet boil temp of
DOT4 is 155 degrees C - if you get your calipers to anywhere near 155C
i bow down to your superior braking! (or pass you on the way down :-),

Probably both. I'm not a fantastically confident descender, so will use the
brakes, and as you noticed I can put twice the energy into them. (Actually
it's potentially more than that, since I can't endo...)

The reason I say the discs aren't fit and forget in the same way as the
magura rims is that I have had to do this sort of crap on them, whereas
the
rims have been sealed since I fitted them 10 years ago, and have never
given
any problems.

Why did you have to bleed it?

Because there was air in it. I think the people who put the tandem-length
pipe on it got it wrong - that was Hope BTW.

It just isnt necessary.

Except it was...

And as
mentioned, it couldnt be an easier task to blow through new fluid, not
like when you get really bad bubbles in and have to get shut of them
too.

Like I did?

There is another question though : is it worth the hassle? And the answer
for the MTB tandem is definitely yes. Can't tell for the road tandem
since
nobody makes suitable hydraulic discs...

I'm missing where the hassle comes in TBH - which was my point from
the start - hydros are the most fit and forget items on any bike I've
owned or maintained!

If you get oil on them then thats carelessness, not the brake at fault

Actually, it's the fork air seal failing and dumping the oil on the brakes.

The sensitivity of the brakes to oil is a definite downside - with care, the
problem can be avoided, but I'm sure you'd agree the it would be better if
it wasn't there in the first place.

I think my discs are set up fairly well - they're definitely straight (I
spent a while getting that right when first installing them, and I'm not
completely mechanically inept.)

cheers,
clive