Won't agitate and makes a grinding noise

check belt under unit if ok check under agitator for bad cog splines

check back of unit as the concrete on the back may of been dislodged check not over loaded also the belt maybe loose or streached

My Maytag Performa makes a grinding sound when it agitates. When it starts to dump the water it makes a loud grinding on metal sound... really loud. What is the problem and how much to fix?

Its probably you stator plate and rotor. But you need special tools for this repair. There a spring that is under 200 pounds of pressure and if you take the screws off that hold the plate its going to fly into you face if your dont use the special tools to depress the spring. Is it more of a clanking kinda of noise? DOes it olnly happen with heavy loads? Try this out. Fill the washer with water only. and get it into a wash cycle with water only. If there is no noise then put in like a load of towels. A heavy load. Now if you hear the noise now then its for sure you stator plate and rotor..hope this helps, but like i said you need those special tools to do this repair or injury can result from the spring part.

possible foreign substance under agitator

is it possible that the washer was overloaded? if so the agitator has little plastic "gears" that move the agitator one way only, they could have made the sound. 
you can also check under the washer to see if anything (like a coat-hanger or something) is interfering with moving parts of the washer

the agitator shaft has come loose from the transmission. when you pushed it back down it probably didn't seat properly, thats why the grinding sound. you need a new transmission

thanks for posting problem solve :0)

If the fill and drain functions correctly, AND the spin cycle works correctly, AND the cycle itself starts and completes correctly, the problem being that the back and forth motion of the agitator starts the loud grinding noise, it will likley be broken gears in the transmission. The single most expensive part in the washing machine.

If you begin dissassembly from the tub down, you wil come to the transmission with the spindle sticking out of it. If you undo the bendable tabs all around the transmission it comes apart in two halves. Careful, its full of oil. The spindle has a plastic gear bolted to the bottom of it. It meshes with other gears in the tranny. It has sheered teath and is making the noise.