Thanks for your answers!!!
You are rigth, U joints are cheaper, and depending on the cv joint, may be stronger.
But i need to replace the axle shafts, because the 4 holes to install each U joint are too big... here in Argentina I can't get new axle shafts, and repairing old ones aren't an easy job...
My English is poor, but I hope you can undestand what i am saying...!!!!
Thanks again!!!