The slip clutch on my bush hog started slipping. There is a large unusual nut that you can see in the attached photos between the gearbox and the slip clutch. It looks like if I tighten that it will increase the pressure on the plates, but how much do I tighten it? And what kind of wrench fits this thing? It looks like it takes some kind of special spanner. I could put a pipe wrench on it, but I'm not sure which way it turns and it's been on there for ages. Or do I just need to replace the friction plates? Any help appreciated.