John Deere is not the company they used to be. I doubt they have a tensioner and if there is it has little, little adjustment. If the belt keeps breaking clean you better bring it in for some warranty work. If it shreds everytime your working it too ...
Call the John Deere house in your area...they will know this...most John Deere Dealers only work on John Deere., and in my area, we don't have those..Texas...but, any John Deere House will be able to tell you...I can work on the engines...anything el...
hahah, sorry, you cannot change the speed of you tractor unless you change the gaering in the transmission or you change the belt system. which if you have time on your hand, haha, go ahead, give it a try. the easiest change would be the pulleys. goo...