That's the Tri-Glide model, which has proven unreliable. Mine failed as have others. Two of the three rollers had failed welds - I came close to losing my trailer. The Tri-Glide has been removed from production. There are three more grease fittings inside the hitch accessible from the backside. And, no, there is no manual of any sort.
If your hitch bangs when you start and stop it's failed. If your hitch looks like this (this one is mine), then it has failed. Mine was replaced with just the Trailair minus the Tri-Glide (under warranty) and it's been working great.