The drum rocks violently?

I have a Hotpoint 9536 wahing machine that would not spin.
I changed the controller board with one that was OK - still no spin.
I replaced the motor which ran.

After reasembling the machine I loaded it up and put it on a cycle, as soon as the drum began to turn the drum rocked violently as though either the brake was on or the drum was siezed up.

With the belt off the drum rotates freely.

Now I am stumpped as to what to look at to cure this problem.