I have recently purchased a 48" Hydro walk behind with sulky. the sulky has two caster wheels that are identical to the casters in the front of the machine. I weigh about 200 lbs. and the damn casters on the sulky just don't turn when i attempt to back the machine up. the result is the tires spin and tear the ever loving god out of the turf. please tell me i am doing something wrong or is it just a poor design. every thing gets greased on a regular basis so i can rule that out. any input?