Hi I bought a 1989 bobcat 643 and it is almost impossible to drive it jumps and jerks around we also have a gehl 3814 for years and itisa fantastic machine very smooth and easy to drive but the bobcat is very dissapointing we replaced chains and bushes in the controle levers butit stillmade no diffirence when you try to drive it is justjerking every where is there anything we can do to solve this problem or are they all the same