David,
I agree with what Paul said. Some guys think that with Bearing Buddy's you just keep pumping till the grease gun's empty.
If you watch the back of the piston push out against the coil spring, and stop injecting grease well before the spring is tolally collapsed you should be allright. Once the spring is totally compressed, you turn the thing into a hydraulic seal removal system! Of course, some idiots will keep adding lube until the entire brakedrum is filled with grease and the wonder why the brakes don't work!
If you suspect the brakes on your trailer are dragging (and overheating), you might try getting the rig up to speed, then putting the tow vehicle into neutral and checking the coast down rate. An empty trailer with no brake drag should not decrease the coast time (you should not be able to tell it's there). If the trailer brakes are dragging even a little, I think you should be able to tell. Just a suggestion.
Steve