The 843s are a very strong and simple machine and should serve you well. I would agree the problem is likely linkage but since your are new to the unit are you sure the safety locks that the lap bar engage when its down are operating properly. I have seen debris lock the pedals and the plastic tops of the locks break off. Normally when the plastic tops break the springs fall out and the pedals operate all the time; can be dangerous getting in and out of a running machine. Good luck and excellent choice with the 843.