Maytag top load agitates only on small load

The washer works great, but only on small and possibly medium loads. On large loads, there is slight spin (in one direction) , but no agitation. This washer does not have dog ears, and replacing the entire agitator ($75-$100) would not be ideal. Thanks in advance for all your time and help!

Pulleys look good, just the transmission part does not move around when the weight hits a certain level. Any ideas, anyone?

Okay I fixed it, and better yet for free. Here is what I did. I took the agitator out and found this black blob of my sons football mud, and plenty of hair from my dog. All this was bonded together with soap scum. I cleaned it all out real good with a flat head screw driver. Now she is running like she is brand-used! Hope this helps someone, someday.