First of you should check to see if you can tighten the idler chains. If you cannot tighten them then you will need to replace them. Just count the number of links and then look around for the chain...local dealer, farm supply store, etc.
If they are already doing a lot of jumping then you may also want to take a look at the teeth on the disc to make sure that the teeth are not worn to much (very pointy like shark teeth). You may also need to replace them as well.
I had the same problem with my machine once when I first got an argo. When I went for a ride ended up shearing all the teeth of one side disc. Had a fun time trying to get back home....
Even if you’re on the right track, you’ll get run over if you just sit there.
—Will Rogers