My 1978 belt driven Whirlpool washer when it engages to agitate instead of going "Grind-click-clunk", it goes "Grind-click-clunk-CLACK", and during the "CLACK" part, it shakes the drain standpipe-it clacks with such force. Do you know what the problem is with my classic washer?
The clutch pads have worn out on the basket drive assemebly, which is just like your brake pads being worn out on your car - only in reverse. Once you get down to a metal on metal condition, there will be slapping and grabbing. This is a serious repair is usually done in conjuntion with replacing the pump & belt, since the complexity of the job is such that you only want to do it once every 2 decades or so.
I have rebuilt a number of these machines and serviced dozens of them over the years. There's even one in my collection which I run about 2 times a year, and she behaves just like a lady.
Also...remember this is just a reading from my crystal ball, and the machine will have to be actually inspected to determine if this prediction is correct.