panasonic NV-FJ710B-wont work in play mode?

Fitted new take up arm/gear assy to this machine due to the teeth shreding of the rack and pinion portion.all other function seem ok ie ffwd/rev etc but tape seems to bunch up when put into play mode and there is a clanking sound from the cassette area as if the gears are not driving corectly.The mechanism is Matsushita dont know if this is common to all panasonic models.Any info eg where to get gear timing info etc would be a help.