i fixed 3 victa 550 self drive mower, those problem are simelar yours. the problem is not on clutch, it is on between body and the top cover of gear box. you can undo the bolt which is under the gear box, it has a spring; and then put a ring between the body and gear box. make sure the top of the gear box and the body is on same level. try,,,,, sorry, my english is not very well, i hope you can understand me. cheers.
jim from new zealand, October 2008