Blade Brake Clutch System; Control Box Operation; Description - Toro 20330 - Low Wheel Walk Power Mower Service Manual

BBC / BOS / BCS

BLADE BRAKE CLUTCH SYSTEM

(BBC)

Description

There are two basic blade clutching system designs.
The fi rst is commonly referred to as the BBC or Blade
Brake Clutch. It has two versions which have been used
on many Toro models as well as Lawn-Boy Medallion
mowers. The second design was introduced in 2005 and
is used on Toro (Blade Override System) and Lawn-Boy
(Blade Clutch System) (Fig. 146 and Fig. 147).
6-2
Fig 146 3428-0001
Fig 147 3428-0004
The blade clutch system offers the customer
convenience to stop the blade while allowing the engine
to continue to run.
Before troubleshooting the BBC deck mechanism, be
sure that it is adjusted properly. Refer to the BBC cable
adjustment section for proper adjustments.
BBC Clutch Operation
The clutch operates by using a fl ywheel which turns with
the engine crankshaft and a brake drum and blade that
are free to turn separately from the fl ywheel. The two
are connected by tensioning a drive belt between the
fl ywheel and brake drum. The combination idler arm and
brake controls the belt. When the control is engaged,
the idler with the brake pad backs away from the brake
drum and tightens the belt. When the control is released,
a spring causes the idler to pivot towards the brake drum
releasing the belt and engaging the brake. This stops the
blade but allows the fl ywheel and crankshaft to continue
to turn.
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. The control mechanism meets
the federal government's "2-step" blade engagement
procedure. The traction drive can also be integrated with
this control system.
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