Exactly! I recognized it as soon as I saw it. It is a 13mm bore Magura
master cylinder common on many BMW and other motorcycles from the early to
mid-eighties. I rebuilt ours using a rebuild kit available through our
local BMW motorcycle dealer. It is very simple to do and it is very
doubtful that you would need it honed - just clean it up with a very fine
silica paper. If you need a complete new cylinder, check with Grob and if
the price seems high, have your local BMW dealer try to order one for you.
They may not be able to get one though given teh age and the fact that it
may not be a BMW part. Most BMW's of the era had square reservoirs on them
and not the round type used in the Grob. This particular Magura may have
actually been from a dirt bike since Magura master cylinders were used by
many manufacturers.

I had to laugh the first time I saw it in the Grob! I imagined a bunch of
German engineers leaned over the glider with slide rules and calipers trying
to design the ultimate brake cylinder when some apprentice walks in holding
the master cylinder he just took off his motorcycle in the parking lot! I
also laughed when these same engineers evenually threw up their hands and
used the brake disc and caliper off a Cessna!!! (Ahhh, the myth of German
enginering prowess exposed!!!)

Bleeding is best done from the caliper by forcing the fluid up. It is
nearly impossible to "pump" out the air bubbles from the top. I learned of
the problems bleeding these Magura cylinders from a motorcycle tech site on
the net. Here's a cheap, easy and effective tool to use. Get a hand pump
like used on a soap dispenser (or go all out and buy a similar plastic hand
pump sold at a marina as a tool for adding oil to the lower case of a marine
outboard motor) and attach a piece of hose from the spout to the caliper
bleed nipple. Screw it on to the plastic brake fluid bottle (fit seems to
be universal) and start pumping. After only a few strokes, the job is done.
You just have to wrap some paper towel around the open reservoir to catch
the excess or use a syringe to draw it off as the level goes up. (Forget
using the syringe from the bottom. It is not as easy as the hand pump since
the back pressure makes it hard to operate.)

After resurfacing the pads and disc as well as the cylinder rebuild, our
Grob now stops like a lawn dart.


"Buck Wild" wrote in message
om...
Ray Lovinggood wrote in message
...
Our club's G-103 Acro needs a new brake master cylinder.
We can probably get one from Grob in Ohio within several
weeks, but we would like to get one sooner.

Does anyone, anywhere, have a master cylinder they
would sell us? Then, we would pay overnight freight
to our club's location in North Carolina, USA.

Please contact me at:

Thanks,
Ray Lovinggood
Carrboro, North Carolina, USA

Ray, that master cylinder is from a BMW motorcycle. It's the front
brake cyl with the hand lever cut short. Im sure you can get it
cheaper than from Grob if you check cycle salvage places.
-Dan