My Craftsman ZTS7500 started bucking again. Its full of oil & purged, not as bad as it was but its getting there. Does the Hydro trans have a pump? If it does it may be clogged or worn out. People may wonder why I have so many hrs on it, 2120 now. I use it every day. I trot my English Bull Terrier a mile or so every morning, on a short leash he will trot along the side of it. I cut 11 acres of grass for a long time then got a commercial Grasshopper. I pull a small trailer to do odd jobs, work in the garden,etc. I'm in the process of planting lawn fescue on 5 acres. A lot of rocks come up after I till the soil, I go around picking up rocks & this takes hrs. I seed with the mower, fertilize, tow a home made rake to pull up the bad grass by the roots. I smooth out the ground & do all sorts of things with it. Not unusual to run it 5 hrs or more a day. The bucking occurs when it starts moving, once the control levers are pushed all the way forward it will smooth out. Any thoughts?