Service Manual
SECTION
4
BLADE
BRAKE AND CLUTCH (BBC)
SYSTEM
introduction
In
1982 the federal government mandated that all
consumer walk behind mowers with a cut of
63.5
cm
(25‘)
or
less
be
equipped with safety devices. There
are
two
primary criteria which these safety devices
must meet.
1. A
two
step operation must be performed
in
order
2. The blade must come to a stop within
3
seconds
One of the ways The Toro Company met these
requirements was with the Blade Brake and Clutch or
BBC System. This system
uses
a clutch on the engine
crankshaft
so
that the blade can freewheel on the
crankshaft.
It
also uses a brake to stop the blade within
3
seconds of when the operator releases the control
bar. This system has the advantage of allowing the
operator to stop the blade without stopping the engine.
The BBC system is somewhat complex,
and
will
therefore be broken down into
4
subsections:
BBC Control Box
BBC Bellcrank System
BBC Deck Mechanism
BBC Cable
to get the blade turning.
of the operator leaving the operator’s position.
BBC CONTROL
BOX
BBC
Control Box Operation
The BBC control mechanism’s purpose is to actuate
the deck mechanism.
It
does this by tensioning and
loosening the BBC cable. While this sounds simple
enough, keep
in
mind that the control mechanism must
also meet the federal government’s ‘2-step’ blade
engagement procedure, and on many models must
also control traction.
First, let’s take a look at normal operation of the BBC
control box. See Figure
74.
The normal or ’at rest’ position
of
the control bar is
indicated by the number 1
in
the previous figure.
In
order to engage the blade, the operator must first
‘cock’ the control
bar
down to position 2, then raise the
control bar to position
3.
Notice that position
3
is approximately 12
cm
(5”)
below
the handle. This distance between position
3
and the
handle is resewed for engagement
of
the transmission
on those models equipped with the self propel. On
units without self-propel the control bar can be lifted to
Vacu-Power Mower
47
the handle without affecting operation of the BBC
system.
GROUND
SPEED
Figure
74
After engagement
of
the blade, release
of
the control
bar causes
it
to drop to the number 1 position which
disengages the blade and, on self-propel models, the
transmission.
Next, let’s take a
look
inside the control
box
at the
various components and identify their function. See
Figure
75
and the corresponding explanations that
follow.
d
Figure
75
BBC System