Small Engines (Lawn Mowers, etc.): Murray 46, murray lawn tractor, tension spring

Question
I have a Murray lawn tractor with 46" cut. After engaging the blades and mowing for a few feet the blades stop rotating. After you back up where you have mowed they start spinning again. When it first started I replaced both belts and it was better but it would slow down sometimes and the speed back up. Then I noticed that some of the bearings were bad . I replaced all 3 spindles with new shafts and blade mounts. Then when I tried to mow it just completely stops.  

Answer
 Hello Larry:

 Send me the Model Numbers and Serial Numbers Off the Mower, Please. It Sounds like a Tension Spring May be Broken/Missing/Weak. With the Model Numbers I can see a Diagram of the Mower Deck and Assist you Better. Thanks.

 Respectfully

 John