M4 9914 tape loading questions

I'm tinkering with the first of the three 9-track units I acquired recently. This is the M4 9914, a seemingly very nice unit in that it was clean, powers up and acts from the front panel buttons, and that it handles 800 BPI as well as 1600 and 6250. Mind you, I'm old enough to still have a stack of tapes that I used in college in the early 80s, but I'm not old enough to have worked behind the counter with the big VAXes and UNIVAC. I might've written a tape or two in person under PDP Unix, but I probably did it under the watchful eyes of someone more experienced. The first time I tried to load a tape, the vacuum fed the tape correctly back to the takeup reel but it was not picked up on the reel. The notched leader on the tape is in good shape, but it did not engage. I unscrewed the top of the takeup reel and was puzzled. I expected to see a mechanism to hook the leader (as you see inside a DLT, for example.) The takeup reel hub is smooth. It does have openings on the lower half, and the hub is certainly part of the vacuum path. Is vacuum alone supposed to grab the tape and hold it to the takeup reel? Most other times I loaded a tape, the tape didn't move smoothly back to the take reel. It bunched up after hitting obstacles along the path. I do not yet have the user or service manuals for the M4 9914. I did find several manuals for similar units (HP 88780) on Bitsavers. I googled quite a bit to find the definitive 9-track history and preservation site but I haven't found it yet... - John