case 15 30 not turning ,but drives in forward and reverse fine ?

[dr.diesel]

I just picked up a case 15 30 and am having an issue with it, so I figured I would post here before digging into it. A little background on the machine. The guy I bought it from replaced the air cooled Wisconsin with a liquid cooled 4 cylinder Toyota gas motor from a sweeper of some sort. He also removed the variable speed drive and made it a single speed. After cleaning the carb up and making some adjustments the skid steer drove off the trailer with no problem. (It was loaded onto my trailer with a forklift as it did not run.) The lift and tilt work, aside from a hose that burts up front for the bucket tilt. The problem with the machine is that it will go forward and reverse with no issue at all, however when you try to turn the machine by moving one drive lever forward and the other in reverse it moves forward, but the side that is in reverse doesn't really move. The weird part at least to me is that if you move both drive levers together in forward or reverse the machine moves in those directions with no issues and at decent speed with no abnormal noises. My plan is to take off the side covers on both dives after putting the machine on blocks and seeing whats going on. Im guessing something with some sort of break or lose chains? I have never worked on an older machine like this but fix just about everything so im sure i can figure it out but any pointers to save a lot of time and effort would be appreciated. Thanks!