bleeding Duo Discus brakes

Looking for advice on bleeding the brakes on my Duo with the tost 30-9
caliper. I replaced a shot bleeder valve with a new stahlbus valve,
but after futzing with the system for over an hour, I can't get the
brake to firm up to an acceptable level.

I've tried using a suction device to pull fluid (Dot 4 in the Duo)
down through the line. I've also gone with my normal old standby of
pushing fluid up through the brake using a syringe. The Stahlbus
valve is not working as advertised or rather the brake isn't. The
brake doesn't seem to be creating enough pressure to overcome the
spring tension on the check valve.

The best I've been able to get to so far is a fairly spongy grip on
the rotor. Enough that turning by hand isn't possible, but it doesn't
feel like it would slow you down much when you needed it.

Basically it just doesn't feel like the master cylinder is drawing
fluid in or maybe there is a hidden air bubble.

Any thoughts from the internet hive on the quirks of this beast?
It's certainly been a much greater hassle than I expected. I'm
guessing at this point that either there is a trick that I don't know
about or something is malfunctioning.

Thanks,

Morgan

Not on the Duo specifically, but some thoughts none-the-less.

Best to use a pressure pot (can be a good quality pump oil can, but
better is a small pump-up garden sprayer modified for the job, as this
allows some serious through-put to overcome and move out bubbles in
high spots).
Cycle the brake lever a few times while pumping the fluid up.

Note that some installations don't have the brake line going into the
caliper at the top, thus there can be a stubborn bubble in the caliper
itself. In this case, remove caliper and but a clamp on piston to keep
it from coming out. Then bleed with brake line at top.

To get more through put, you will need remove all brake fluid from the
reservoir with a syringe. Better is to intall a fitting in the
existing cap vent hole so you can install a temporary tube to take off
the excess brake fluid. Depending on existing cap vent hole, you may
be able to use a large hypodermic needle for this (McMaster-Car sells
them 1/8" OD) or you can drill hole bigger and install a nipple to
accept the vent tube. Pump brake fluid up until no more bubbles exit
vent tube - - which can be placed in a container so bubbles are
clearly visible.

Interesting that the Duo uses automotive Dot fluid?? I know the Stemme
does also. Schleicher uses the more common (at least in the USA for
small GA) Mil Spec 5606 fluid (the good ole red stuff). You cannot mix
or substitute the two as 5606 calls for Buna-N seals and O-rings,
while Dot fluid takes EPDM rubber seals.

Tost buys some US Cleavland brake parts, such as the 30- series
caliper, and replaces the Buna-N O-rings with EPDM. The Cleveland
calipers, and their early non-anodized pistons, tend to corrode due to
moisture as the Dot fluids are hygroscopic. Later pistons, after the
mid-90's or so, are anodized, but the caliper bore is still prone to
corrode when Dot fluids are used, and this leads to leaks and poor
braking. So be sure to check caliper bore condition if using Dot
fluids. The long term fix is to sleave the bores with brass liners and
anodize the pistons if they're the early ones.

bumper
MKIV & QV
Minden

On Jan 11, 12:54*am, bumper wrote:
Not on the Duo specifically, but some thoughts none-the-less.

Best to use a pressure pot (can be a good quality pump oil can, but
better is a small pump-up garden sprayer modified for the job, as this
allows some serious through-put to overcome and move out bubbles in
high spots).
Cycle the brake lever a few times while pumping the fluid up.

Note that some installations don't have the brake line going into the
caliper at the top, thus there can be a stubborn bubble in the caliper
itself. In this case, remove caliper and but a clamp on piston to keep
it from coming out. Then bleed with brake line at top.

To get more through put, you will need remove all brake fluid from the
reservoir with a syringe. Better is to intall a fitting in the
existing cap vent hole so you can install a temporary tube to take off
the excess brake fluid. Depending on existing cap vent hole, you may
be able to use a large hypodermic needle for this (McMaster-Car sells
them 1/8" OD) or you can drill hole bigger and install a nipple to
accept the vent tube. Pump brake fluid up until no more bubbles exit
vent tube - - which can be placed in a container so bubbles are
clearly visible.

Interesting that the Duo uses automotive Dot fluid?? I know the Stemme
does also. Schleicher uses the more common (at least in the USA for
small GA) Mil Spec 5606 fluid (the good ole red stuff). You cannot mix
or substitute the two as 5606 calls for Buna-N seals and O-rings,
while Dot fluid takes EPDM rubber seals.

Tost buys some US Cleavland brake parts, such as the 30- series
caliper, and replaces the Buna-N O-rings with EPDM. The Cleveland
calipers, and their early non-anodized pistons, tend to corrode due to
moisture as the Dot fluids are hygroscopic. Later pistons, after the
mid-90's or so, are anodized, but the caliper bore is still prone to
corrode when Dot fluids are used, and this leads to leaks and poor
braking. So be sure to check caliper bore condition if using Dot
fluids. The long term fix is to sleave the bores with brass liners and
anodize the pistons if they're the early ones.

bumper
MKIV & QV
Minden

After replacing the seals on my Discus 2 hydraulic brake, the only way
we could bleed the system was to pump upwards from the bottom to
remove some stubborn air bubbles. It was a pig to do and took a long
time to get it properly working.

I have no idea why your syringe would not work, but all of Bumper's
suggestions sound good.

Mike

Bumper and Mike thanks for the suggestions. Adding the automatic vent
to the top of the cap sounds like a good move. I have pumped the
reservoir full from the bottom and wasn't seeing bubbles, but maybe
there is a big one hiding and being able to push more volume sounds
like a reasonable start. I have a big syringe from the pet store
that probably holds 3x the capacity of the system, but the reservoir
at the top becomes the limiting factor. The garden sprayer is another
great tip.

The caliper is mounted near vertical. I may pull it just to orient it
better and eliminate that variable.

Thanks again for the suggestions.

Morgan

Good luck . . .

And if it is Dot fluid, be really careful about clean up, given some
time this stuff is as good a paint remover as anything else. Once upon
a long time ago, I thought I was being fastidious cleaning up and used
compressed air to blow out one of the tubes I'd used for bleeding. The
little bits of brake fluid spray settled unnoticed on my car hood and
fender some 25 feet away. Next morning that car had a serious case of
the measels.

bumper

IIRC, note not all Duos have the same setup as SH have
tried to improve it a few times now...

On Wednesday, January 11, 2012 11:10:10 AM UTC-5, Morgan wrote:
The caliper is mounted near vertical. I may pull it just to orient it
better and eliminate that variable.

Right, its still got a cavity trapping air in the mounted position.

Be careful with the adjustments.
Things I have seen, which you REALLY want to avoid:

(1) adjustment so that vent in top of master is blocked;
this is supposed to be a normally open system.

(2) adjustment so that the spoiler travel is restricted;
check that the spoilers can come full out (cases some
complaints about Duo spoilers !)

Hoe that helps,
Best Regards, Dave "YO electric"

On Jan 11, 9:40*am, Dave Nadler wrote:
IIRC, note not all Duos have the same setup as SH have
tried to improve it a few times now...

On Wednesday, January 11, 2012 11:10:10 AM UTC-5, Morgan wrote:
The caliper is mounted near vertical. I may pull it just to orient it
better and eliminate that variable.

Right, its still got a cavity trapping air in the mounted position.

Be careful with the adjustments.
Things I have seen, which you REALLY want to avoid:

(1) adjustment so that vent in top of master is blocked;
this is supposed to be a normally open system.

(2) adjustment so that the spoiler travel is restricted;
check that the spoilers can come full out (cases some
complaints about Duo spoilers !)

Hoe that helps,
Best Regards, Dave "YO electric"

I have a Nimbus which I assume isn't too different regarding the
brakes. I rebuilt the entire brake system last winter and found that
using the oversize veterinary syringe and pushing fluid from the
bottom works well as long as the caliper is off the gear and oriented
so that the brake line port points straight up. Schemp does use DOT
fluid. I didn't find any severe pitting of the caliper or pistons,
but it's worth looking out for.

Best regards,
Craig

I'll pull the caliper before my next bleed attempt. I also picked up
a pump bottle and some hardware to potentially make this easier to do
solo.

My issue is probably made worse by the angle of the glider in the
driveway which causes it to sit very high in the cradle making the
angle to the caliper even farther off 90. I suspected that might be
contributing to the issue, and the comments would confirm that it
probably isn't helping.

I appreciate all of the feedback and support.

Morgan

On Jan 11, 12:30*am, Morgan wrote:
Looking for advice on bleeding the brakes on my Duo with the tost 30-9
caliper. *I replaced a shot bleeder valve with a new stahlbus valve,
but after futzing with the system for over an hour, I can't get the
brake to firm up to an acceptable level.

I've tried using a suction device to pull fluid (Dot 4 in the Duo)
down through the line. *I've also gone with my normal old standby of
pushing fluid up through the brake using a syringe. *The Stahlbus
valve is not working as advertised or rather the brake isn't. *The
brake doesn't seem to be creating enough pressure to overcome the
spring tension on the check valve.

The best I've been able to get to so far is a fairly spongy grip on
the rotor. Enough that turning by hand isn't possible, but it doesn't
feel like it would slow you down much when you needed it.

Basically it just doesn't feel like the master cylinder is drawing
fluid in or maybe there is a hidden air bubble.

Any thoughts from the internet hive on the quirks of this beast?
It's certainly been a much greater hassle than I expected. *I'm
guessing at this point that either there is a trick that I don't know
about or something is malfunctioning.

Thanks,

Morgan

Hi All, I have owned a lot of SH gliders and have had success doing
the following -
unbolt the brake cylinder and raise it up so there is no "loop" in the
brake line -
so the path from the brake calipers to the brake cylinder goes only
uphill -
first try to actuate the brake cylinder lever - sometimes this will
"burp" the air
bubble up into the brake cylinder - otherwise fill fluid from the
bottom nipple
until the air bubble goes into the brake cylinder reservoir - most
times the
air bubble will burp into the reservoir and no filling is necessary -
good luck,
Ralph Woodward

This pretty much nails what ended up working for me. I ended up
removing the whole system from the ship and flushing it forwards and
backwards to make sure there wasn't any old fluid or particles in the
system. Popped the piston out and inspected it and the cylinder wall
for corrosion and pitting. Overall things looked pretty good, but it
got a good cleaning while I was in there.

Funny, you'll jump through all sorts of hoops and delays to avoid
doing it the "hard way" and in the end that was the least traumatic
and fastest way to get it to work. It took me way longer than it
should have, but the upside is that I know my braking system inside an
out now and it is time for new pads as well.

Thanks for the tips.

Morgan




On Jan 16, 9:23*am, rhwoody wrote:
On Jan 11, 12:30*am, Morgan wrote:









Looking for advice on bleeding the brakes on my Duo with the tost 30-9
caliper. *I replaced a shot bleeder valve with a new stahlbus valve,
but after futzing with the system for over an hour, I can't get the
brake to firm up to an acceptable level.

I've tried using a suction device to pull fluid (Dot 4 in the Duo)
down through the line. *I've also gone with my normal old standby of
pushing fluid up through the brake using a syringe. *The Stahlbus
valve is not working as advertised or rather the brake isn't. *The
brake doesn't seem to be creating enough pressure to overcome the
spring tension on the check valve.

The best I've been able to get to so far is a fairly spongy grip on
the rotor. Enough that turning by hand isn't possible, but it doesn't
feel like it would slow you down much when you needed it.

Basically it just doesn't feel like the master cylinder is drawing
fluid in or maybe there is a hidden air bubble.

Any thoughts from the internet hive on the quirks of this beast?
It's certainly been a much greater hassle than I expected. *I'm
guessing at this point that either there is a trick that I don't know
about or something is malfunctioning.

Thanks,

Morgan

Hi All, *I have owned a lot of SH gliders and have had success doing
the following -
unbolt the brake cylinder and raise it up so there is no "loop" in the
brake line -
so the path from the brake calipers to the brake cylinder goes only
uphill -
first try to actuate the brake cylinder lever - sometimes this will
"burp" the air
bubble up into the brake cylinder - otherwise fill fluid from the
bottom nipple
until the air bubble goes into the brake cylinder reservoir - *most
times the
air bubble will burp into the reservoir and no filling is necessary -
good luck,
Ralph Woodward