Toro 20330 Service Manual - Page 88

BBC / BOS / BCS BLADE BRAKE CLUTCH SYSTEM (BBC) Description There are two basic blade clutching system designs. The first 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). 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 flywheel which turns with the engine crankshaft and a brake drum and blade that are free to turn separately from the flywheel. The two are connected by tensioning a drive belt between the flywheel 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 flywheel and crankshaft to continue to turn. Fig 146 BBC Control Box Operation 3428-0001 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. Fig 147 3428-0004 6-2 WPM Drive Systems Manual