Cerutty took him from 4:40 to about 4:10. During Helsinki Landy met Zatopek and decided to train like him. He ran vast amounts of 600 yard intervals at night on a track near his home. After 10 weeks of doing that (without Cerutty) he ran 4:02.1 (59,62,62,59). He then ran 4:02-4:04 about 7-10 times. Then he traveled to a fast track with competition (Chataway) and ran 3:57.9. (58,60,58,62). Just before that he had ran a mile with splits of 56,59,62,65.
I think the breakup had to do with Cerutty yelling at Landy in front of his parents for not qualifying for the final after Landy ran his 4:02. Something like "couldn't qualify for a final in 4:10 and comes home like a whipped dog then does this"
I would say that Landy learning about the more scientific training of Zatopek caused him to realize how stupid it was running around barefoot with sticks yelling like indians. I think Landy just coached himself after that and mainly trained alone. Cerutty is definitly a good coach though-after all he did train Herb Elliot.