how to fix a mtd yard tractor rearend model#13AF608G082?

put new gears top to pully drive and forward gear act perfect in reverse forward wines so loud cant stand it it will drive but doesnt seem to be engaging properly tried adjusting gets no better just worse had universal checked by driggers small engines diagnosed as fine dont understand what it could be dosent seem to be missing anything please help me have an acre to mow and cant afford a new one