Function - description
When the foot pedal is depressed the piston is
moved forwards.
The primary sleeve (2) passes over the equalis-
ing passage (3).
This causes pressure to rise in chamber A, and to
be exerted on piston (4).
As movement continues, primary sleeve (5) passes
over equalising passage (6).
The pressure is now the same in chambers A and B.
Chamber A operates the front wheel brakes.
Chamber B operates on both rear and front wheel
brakes.
If one brake circuit should fail, pedal travel will increase
considerably.
If one brake circuit fails, pressure will rise in cham-
ber A and piston (1) will cause piston (4) in the pressureless
chamber B to be pressed against the dual master cylinder
housing, thus operating the first brake circuit.
If the front brake circuit should fail, piston (1) in the pres-
sureless chamber A will be pressed against the spring cap
(7) and the second brake circuit will be fully effective by
way of chamber B.

Block the outlets from the brake fluid reservoir with two
pointed wooden sticks.
Pull off the hoses at the master cylinder and raise the free
ends above the fluid level.
Warning: Do not tilt the pipe bend when removing, but
pull off carefully while keeping vertical. If carelessly
removed, the pipes may fracture at the bend.

Detach the brake lines:
1 front right 2nd brake circuit
2 front left 2nd brake circuit
3 front right 1st brake circuit
4 front left 1st brake circuit
5 rear brakes 1st brake circuit
Unscrew the master cylinder from the brake unit.
When installing: Check correct seating of sealing plugs

in master cylinder and examine pipe bends for damage.

When installing: Check condition of rubber sealing ring (1).
If the ring is defective no vacuum will be built up.
When replacing master cylinder: check clearance between
thrust rod and master cylinder piston with plastigage and
if necessary set to 0.5 mm (0.02 in.) with a shim (2) behind
the plunger head.
Bleed the brakes (34 00 046).


34 00 046