I replaed the blade drive mandrel and reattacheed the blade and the blade does not freelyturn t is so bound up tht I cannot turnit manually

The answer may be the blade breaks on the mower deck. If you have completely reassembled the mower deck assembly to include the pulleys make sure the breaks are in the correct position or they will bind and lock the blades. If you have bolted on the mandrels and pulleys only and the blades will not turn you may have left the pulley spacer off. This has to be on the pulley end of the mandral to prevent contact between the pulley and fixed portion of the mandral. A quick test would be to losen your pulley bolt to see if this frees your blades. Good luck with your issue.

Okay check see if brakes is on the mower, not the tractor but the blades of the mower deck if not then take belt off of the new mandrel side and try turning blade by hand. should turn freely if not mandrel is bad but unlikely. sounds like you changed wrong side mandrel I presume you have 2 blades and mandrels. or when you installed it back on. the belt may be bound up between a guide and pulley just kind of look things over before a tear apart. and then do your tear apart one step at a time then check blade to see if it turns does not seem serious you may have put belt on wrong, I have done it my self. hope this helps major note do not do this with engine running cut you hand off in a flash.