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.