when the top soil or surface is stripped of dirt the remaining clay hardpan is impermeable by moisture, water, its why farmers will take a deep shanked ripper and loosen the top ft to 16 inches of the soil.
Steve, I can rent a 32HP tractor pretty cheaply with either a box blade (with rippers), a 5' disk, or a roto-tiller. (There is not much down-pressure on a 5' disk to break true hardpan. The roto-tiller is very effective, but would be slow for 9000 sq. feet.)
You could probably rip up a little good topsoil from a borrow area and spread a little on your clay with the FEL. Then break up your clay and over-seed.
They let me take the tractor and implement out over the whole weekend for just the daily rate if I only put 8 hours on the meter. (I just checked my current rates. $150/day for JD tractor, $30/day for box blade, plus $ for trailer.)
If you finish your clay job in less time, you can probably use the tractor for some other projects at your place!
