I didn’t want the title to be forty words long so I’ll keep the details here. I replaced my deck belt a few weeks ago. While mowing it seemed the blades were spinning and then losing speed, then they would catch back up. II was pretty much done and decided to lower the deck a bit to get this one area a little shorter and then the belt jumped off the pulleys and started shredding. Obviously a new belt is in order but I wanted to ask on here what sort of troubleshooting I can do to try and isolate the problem without buying unnecessary parts. I assume it could be the pulleys, the spindles, some sort of alignment issues but I really don’t know enough about tractors like this.

The MTD model is 13AK673G088

 

Look for places it's rubbing with the lever in the on position. Probably against one of the belt guides on one of the center idler pulleys or the guide bar up at the engine pulley.

 

Remove the belt and spin the blades by hand, should be able to spin them with one finger.

 

Thank you both very much. I’ll get it in the air in my garage tomorrow and start checking things out.

 

Make sure the belt is the correct length and cross section for the pulleys, Insure the belt tensioner is free to pivot thru its full arc.

 

I don't think these MTD Decks have a Tensioner or Idler Pulley; they engage and disengage as they're lowered or raised, so having the correct belt length is absolutely critical.

This sounds like some foreign object is involved . . . . or there's some mis-routing of the belt.

I have one of these mowers and I always dread the deck removal and belt replacement process . . . . in comparison of the design of another mower I have made by Murray.

 

Yeah, I just looked at a diagram for that model and it doesn't have the idlers, it's the older style with just an engine pulley and two blade pulleys. Still, check for something rubbing the belt. It might just have been time for the belt to go.