1st reduct gear screaming

[old diesel]

have a late model a jdeere , the 1st reduction gear got so worn(spline) it would strike the housing sometime. even with this much ware there was no gear noise. i put a matching set from other tractor (correct gear and whole clutch assym) now you can hear the gear noise before you hear the tractor with a 4in straight pipe. help what did i do ?

 

[Machinery-Man]

the heal and crown are worn out of the gears and you just have flat surfaces raking together.