Small Engines (Lawn Mowers, etc.): toro blade brake clutch

Question
Working on a Toro GTS 20624 self propelled push mower.  The blade is slow to engage and then when you mow if the grass has any thickness, the blade slows way down almost like the blade brake is engaging.  Also the toro is noted for the "bang" when the brake engages and I am not hearing that.  What should I be looking for to check in this situation?  Thanks

Answer
Have you downloaded the service manual from the URL below?

http://www.toro.com/en-us/parts/Pages/PartsDetails.aspx?mybeid=1448&serialNumber

The URL below may be be closer to your model:
http://www.amopower.com/Toro%20Lawn-Boy%20Walk%20Behind%20Power%20Mower%20Drive%

The most common problem we find are wore belts or old cables that stop properly working...they get dirty and rusty and need to be replaced every now and then.

Have you checked the belt and engagement cable?
Eric