Clutches issues, on Tedder Rake

I have a Fransgard Tedder Rake, and the clutches, seem to be, doing a lot of slipping. There is a greese fitting, on the Tractor Side, of the clutch. What I was wondering, is it the greese, that forces the clutch plates, together? I've always put greese in the clutch, but maybe not enough. Your I put, is greatly appreciated. Thanks in advance.

Clutches issues, on Tedder Rake