Grob 103 Twin II Brake Master Cylinder

The only way I ever got a Grob brake to bleed properly was to use a
pressure bleeder where fluid is forced up through the system from the
slave cylinder. Not too expensive from Spruce & Specialty.
JJ

Mike McCarron wrote:
JJ,

I used Dot 3 fluid with compatible O ring on the slave cylinder. The cap
on the BMW master cylinder said to use DOT 3/4 brake fluid only.

MC

At 14:22 22 October 2008, JJ Sinclair wrote:
Why didn't it work, Mike? Hydraulics are hydraulics, the Clevland
brake slave cylinder doesn't know (or care) where that pressure is
coming from? Make sure you have compatible seals. What type fluid does
BMW use? Can't mix the red stuff with the clear stuff.
JJ

Mike McCarron wrote:
JJ,

I did purchase a master cylinder from a BMW motorcycle dealer that did
fit
in place. Unfortunately it did not function properly. It was
properly
bled and all but it did not work. I don't know what to do next.
There
must be at least 100 of these gliders in the US that will need a
master
cylinder replacement in the future. I don't see how we can junk a
$30K
glider for lack of a functioning master cylinder.

Thanks for your comment,

MC

At 13:41 22 October 2008, JJ Sinclair wrote:
If memory serves me, its a motorcycle master cylinder BMW? I believe
they cut it down from the original, good luck getting your inspector
to sign off on installing it!
JJ

Mike McCarron wrote:
My club has a 1983 Grob 103 Twin II that needs a new master
cylinder.
Over
the years the Grob factory has made changes to the system without
full
documentation and as a result the US distributor can not be sure of
how
I
go about purchasing the proper master cylinder for this glider.

If you or anyone you know has replaced the master cylinder on a
vintage
Grob 103 Twin II recently I would appreciate your input on where I
might
purchase the correct system.

Thank you,

Mike

there is now a new bleeder system from TOST
for details please see http://www.wingsandwheels.com/page32.htm
tim
Please visit the Wings & Wheels website at www.wingsandwheels.com

"Mike McCarron" wrote in message
...
How can one tell where to position the lever? Half way through it's total
travel or some other location?

MC

At 16:33 22 October 2008, Uncle Fuzzy wrote:
On Oct 22, 8:22=A0am, Uncle Fuzzy wrote:
On Oct 22, 8:01=A0am, "bumper" wrote:





Yup, what JJ said. The "red stuff" is Mil Spec 5606 hydraulic oil
and
i=
s
compatible with Buna-N O-rings and seals. It's also commonly used
in
th=
e USA
for most small GA aircraft.

DOT automotive brake fluid, the "clear stuff", most often
glycol-ether
based, and is compatible with EPDM rubber seals.

If you are switching parts from one fluid to the other, you gotta
chang=
e the
rubber stuff.

bumper

"JJ Sinclair" wrote in message


..=
..

Why didn't it work, Mike? Hydraulics are hydraulics, the Clevland
brake slave cylinder doesn't know (or care) where that pressure
is
coming from? Make sure you have compatible seals. What type fluid
doe=
s
BMW use? Can't mix the red stuff with the clear stuff.
JJ

Mike McCarron wrote:
JJ,

I did purchase a master cylinder from a BMW motorcycle dealer
that
d=
id
fit
in place. =A0Unfortunately it did not function properly. =A0It
was
p=
roperly
bled and all but it did not work. =A0I don't know what to do
next.
=
=A0There
must be at least 100 of these gliders in the US that will need a
mas=
ter
cylinder replacement in the future. =A0I don't see how we can
junk
a=
$30K
glider for lack of a functioning master cylinder.

Thanks for your comment,

MC

At 13:41 22 October 2008, JJ Sinclair wrote:
If memory serves me, its a motorcycle master cylinder BMW? I
believ=
e
they cut it down from the original, good luck getting your
inspecto=
r
to sign off on installing it!
JJ

Mike McCarron wrote:
My club has a 1983 Grob 103 Twin II that needs a new master
cylin=
der.
Over
the years the Grob factory has made changes to the system
without=
full
documentation and as a result the US distributor can not be
sure
=
of
how
I
go about purchasing the proper master cylinder for this
glider.

If you or anyone you know has replaced the master cylinder on
a
vintage
Grob 103 Twin II recently I would appreciate your input on
where
=
I
might
purchase the correct system.

Thank you,

Mike- Hide quoted text -

- Show quoted text -

In our club Grob 103, the master cylinder is a Magura motorcycle front
brake master cylinder. =A0Magura makes parts for a bunch of bikes, and
for the aftermarket. Motorcycle front brake master cylinders come in a
variety of piston diameters. =A0They are also somewhat weird to bleed.
They won't develop pressure unless almost all of the air is bled out
of the system. =A0"Pumping" one endlessly has no effect. =A0On a
bike,
on=
e
trick is to zip tie the handle so that the lever is halfway to the
grip, crack the bleeder on the caliper (with a tube on it to direct
the drainage), and walk away for a couple hours and let gravity do
some work for you. =A0Much quicker is to zip tie the lever halfway,
and
use a small vacuum pump rig to PULL the fluid through. =A0Once most of
the air is gone, you should be able to develop some pressure to
complete the bleeding in the normal manner. =A0YES to DOT 3/4. =A0NO
to
Mil Spec 5606 hydraulic oil. =A0As an experiment, I tossed some
motorcycle brake bits in a jar of 5606. =A0They turned into something
other than brake bits pretty quickly.- Hide quoted text -

- Show quoted text -

Clarification on the quicker way to purge the air out: Zip tie the
lever at half travel, use a vacuum pump ON THE CALIPER BLEEDER to pull
brake fluid through. Hope this helps

On 22 Oct, 19:05, "Tim Mara" wrote:
there is now a new bleeder system from TOST
for details please seehttp://www.wingsandwheels.com/page32.htm
tim
Please visit the Wings & Wheels website atwww.wingsandwheels.com

"Mike McCarron" wrote in message

...



How can one tell where to position the lever? *Half way through it's total
travel or some other location?

MC

At 16:33 22 October 2008, Uncle Fuzzy wrote:
On Oct 22, 8:22=A0am, Uncle Fuzzy *wrote:
On Oct 22, 8:01=A0am, "bumper" *wrote:

Yup, what JJ said. The "red stuff" is Mil Spec 5606 hydraulic oil
and
i=
s
compatible with Buna-N O-rings and seals. It's also commonly used
in
th=
e USA
for most small GA aircraft.

DOT automotive brake fluid, the "clear stuff", most often
glycol-ether
based, and is compatible with EPDM rubber seals.

If you are switching parts from one fluid to the other, you gotta
chang=
e the
rubber stuff.

bumper

"JJ Sinclair" *wrote in message

...=
..

Why didn't it work, Mike? Hydraulics are hydraulics, the Clevland
brake slave cylinder doesn't know (or care) where that pressure
is
coming from? Make sure you have compatible seals. What type fluid
doe=
s
BMW use? Can't mix the red stuff with the clear stuff.
JJ

Mike McCarron wrote:
JJ,

I did purchase a master cylinder from a BMW motorcycle dealer
that
d=
id
fit
in place. =A0Unfortunately it did not function properly. =A0It
was
p=
roperly
bled and all but it did not work. =A0I don't know what to do
next.
=
=A0There
must be at least 100 of these gliders in the US that will need a
mas=
ter
cylinder replacement in the future. =A0I don't see how we can
junk
a=
$30K
glider for lack of a functioning master cylinder.

Thanks for your comment,

MC

At 13:41 22 October 2008, JJ Sinclair wrote:
If memory serves me, its a motorcycle master cylinder BMW? I
believ=
e
they cut it down from the original, good luck getting your
inspecto=
r
to sign off on installing it!
JJ

Mike McCarron wrote:
My club has a 1983 Grob 103 Twin II that needs a new master
cylin=
der.
Over
the years the Grob factory has made changes to the system
without=
full
documentation and as a result the US distributor can not be
sure
=
of
how
I
go about purchasing the proper master cylinder for this
glider.

If you or anyone you know has replaced the master cylinder on
a
vintage
Grob 103 Twin II recently I would appreciate your input on
where
=
I
might
purchase the correct system.

Thank you,

Mike- Hide quoted text -

- Show quoted text -

In our club Grob 103, the master cylinder is a Magura motorcycle front
brake master cylinder. =A0Magura makes parts for a bunch of bikes, and
for the aftermarket. Motorcycle front brake master cylinders come in a
variety of piston diameters. =A0They are also somewhat weird to bleed.
They won't develop pressure unless almost all of the air is bled out
of the system. =A0"Pumping" one endlessly has no effect. =A0On a
bike,
on=
e
trick is to zip tie the handle so that the lever is halfway to the
grip, crack the bleeder on the caliper (with a tube on it to direct
the drainage), and walk away for a couple hours and let gravity do
some work for you. =A0Much quicker is to zip tie the lever halfway,
and
use a small vacuum pump rig to PULL the fluid through. =A0Once most of
the air is gone, you should be able to develop some pressure to
complete the bleeding in the normal manner. =A0YES to DOT 3/4. =A0NO
to
Mil Spec 5606 hydraulic oil. =A0As an experiment, I tossed some
motorcycle brake bits in a jar of 5606. =A0They turned into something
other than brake bits pretty quickly.- Hide quoted text -

- Show quoted text -

Clarification on the quicker way to purge the air out: *Zip tie the
lever at half travel, use a vacuum pump ON THE CALIPER BLEEDER to pull
brake fluid through. *Hope this helps- Hide quoted text -

One possibly non-obvious thing is that if there are flexible
rubber hoses in the pressure side of the system they you
need to check that they are servicable.

With age they lose stiffness and expand sufficiently under
pressure such that the brakes do not work. Indistinguisable
symptoms from air in the system.

If you have one that is 30 years old then I would just get a new one.

I don't suppose that the fancy teflon ones suffer from this.
http://www.goodridge.co.uk/buy-goodridge-hoses.htm

1 The master cylinder in the Grob103 Acro is a BMW front brake master
cylinder from a R series motorcycle. The actuating lever is the cut off
front brake lever.

2 It is virtually impossible to bleed the brakes in the normal way and the
following method is used by the Royal Air Force techies who service the 99
Grobs owned by the RAF

a. Cover the open master cylinder in the cockpit with a cloth, important
if you do not want fluid all over the floor.

b With the slave unit removed from the wheel but attached to the pipe
remove the slave piston from the cylinder.

c Turn the unit so the slave cylinder is facing upwards and fill with
DOT3/4 fluid, it tells you the correct one on the master cylinder cover.
Make sure that the bottom of the cylinder is the lowest point.

d Insert the piston and very slowly push completely home in the cylinder,
and I do mean very slowly forcing fluid and any trapped air upwards into
the master cylinder. Clean up the slave and reassemble.

e Fill the master cylinder in the normal way.

Saves spending a fortune on specialist tools which may or may not work.

Soaring Oxford Ltd. Fosse Rd, Syerston, Newark, Nottinghamshire NG23 5NG.
Tel: +441636 525318 are the UK suppliers and supply the RAF. They may help
in sourcing the correct cylinder.

This thread started with the necessity of replacing the brake master
cylinder, right? Did anyone mention why it needed replacement? My first
guess is wear or corrosion in the cylinder bore causing it to leak
pressure. If this is the case, there are places that will bore the
cylinder and sleeve it with either stainless steel or brass. It's done
all the time for old cars.

On the other hand, I don't know anything about the legality of doing that
for an aircraft brake system. And on the Gripping Hand, I would probably
do it that way myself.

Jim Beckman

There's a thread about this he

http://www.aviationbanter.com/archiv...p/t-22487.html


some old G103 maintenance manual on the web http://tinyurl.com/G103MM
doesn't mention anything about changing brake fluid every two years as is
common in most cars, however the DG505 needs it done every 4 years.
http://tinyurl.com/5zy2wj












At 13:00 23 October 2008, Jim Beckman wrote:

This thread started with the necessity of replacing the brake master
cylinder, right? Did anyone mention why it needed replacement? My
first
guess is wear or corrosion in the cylinder bore causing it to leak
pressure. If this is the case, there are places that will bore the
cylinder and sleeve it with either stainless steel or brass. It's done
all the time for old cars.

On the other hand, I don't know anything about the legality of doing
that
for an aircraft brake system. And on the Gripping Hand, I would
probably
do it that way myself.

Jim Beckman

There's a thread about this he

http://www.aviationbanter.com/archiv...p/t-22487.html


some old G103 maintenance manual on the web http://tinyurl.com/G103MM
doesn't mention anything about changing brake fluid every two years as is
common in most cars, however the DG505 needs it done every 4 years.
http://tinyurl.com/5zy2wj












At 13:00 23 October 2008, Jim Beckman wrote:

This thread started with the necessity of replacing the brake master
cylinder, right? Did anyone mention why it needed replacement? My
first
guess is wear or corrosion in the cylinder bore causing it to leak
pressure. If this is the case, there are places that will bore the
cylinder and sleeve it with either stainless steel or brass. It's done
all the time for old cars.

On the other hand, I don't know anything about the legality of doing
that
for an aircraft brake system. And on the Gripping Hand, I would
probably
do it that way myself.

Jim Beckman

On Oct 23, 7:15*am, P Ilatus wrote:
There's a thread about this he

http://www.aviationbanter.com/archiv...p/t-22487.html

some old G103 maintenance manual on the webhttp://tinyurl.com/G103MM
doesn't mention anything about changing brake fluid every two years as is
common in most cars, however the DG505 needs it done every 4 years.http://tinyurl.com/5zy2wj

At 13:00 23 October 2008, Jim Beckman wrote:





This thread started with the necessity of replacing the brake master
cylinder, right? *Did anyone mention why it needed replacement? *My
first
guess is wear or corrosion in the cylinder bore causing it to leak
pressure. *If this is the case, there are places that will bore the
cylinder and sleeve it with either stainless steel or brass. *It's done
all the time for old cars.

On the other hand, I don't know anything about the legality of doing
that
for an aircraft brake system. *And on the Gripping Hand, I would
probably
do it that way myself.

Jim Beckman- Hide quoted text -

- Show quoted text -

I wouldn't let it go that long myself. I change the brake fluids (all
fluids really) in my bike every year. It's the water accumulated in
the automotive brake fluid that causes the corrosion that kills the
cylinders.

"Jim Beckman" wrote in message
...

This thread started with the necessity of replacing the brake master
cylinder, right? Did anyone mention why it needed replacement? My first
guess is wear or corrosion in the cylinder bore causing it to leak
pressure. If this is the case, there are places that will bore the
cylinder and sleeve it with either stainless steel or brass. It's done
all the time for old cars.

On the other hand, I don't know anything about the legality of doing that
for an aircraft brake system. And on the Gripping Hand, I would probably
do it that way myself.

Jim Beckman


One shop that does a good job with this is:

http://www.brakecylinder.com/

Part of the problem, as has been posted before, is that DOT brake fluids are
hygroscopic. If brake parts are aluminum, then water in the fluid can
promote corrosion. Anodizing the aluminum parts, or sleeving them in the
case of caliper housings, can help prevent this. To test to see if a given
part is anodized, say a piston from a caliper, touch the part with the leads
from a ohm meter (digital meter set on ohms). The anodize layer is an
insulator and won't conduct.

bumper
QV and MKII

At 13:00 23 October 2008, Jim Beckman wrote:

This thread started with the necessity of replacing the brake master
cylinder, right? Did anyone mention why it needed replacement? My
first
guess is wear or corrosion in the cylinder bore causing it to leak
pressure. If this is the case, there are places that will bore the
cylinder and sleeve it with either stainless steel or brass. It's done
all the time for old cars.

On the other hand, I don't know anything about the legality of doing
that
for an aircraft brake system. And on the Gripping Hand, I would
probably
do it that way myself.

Jim Beckman

Old cars normally have steel brake cyliders, the BMW part we are talking
about is aluminium. Putting a steel or brass sleeve in will almost
certainly cause corrosion (disimilar metals).
A new part is available and is not expensive. All that needs to be done is
to swap over the lever.