My problem now has to do with pocket doors, but first a little background.
My house was built in 1965 and includes several flat-panel mahogany pocket doors. Most of them no longer ride in and out smoothly and quite frankly, I'd just like to remove them and build in plain door frames. There is a double pocket door opening between my dining room and living room. That wall runs down the middle of the house, which I assume is load-bearing. Twice in the last six years, after a very dry summer, the double door opening shifts or flexes making large cracks in the drywall at the top corners of the frame. It also binds up the doors and prevents them from sliding open. I assume that this has to do with the inherent weakness of a hollow wall, hiding the pocket doors, either side of the opening.
My question is this: How can I strengthen this door frame, and the others in the house, after removing the pocket doors? Should I tear out drywall and add studs? Or is any of this even necessary? It seems to me the large opening needs support.
Older pocket doors falling off their tracks, or going out of adjustment is a common problem. There were a few types of track and roller systems used, with one type being less expensive and more prone to failure. I will address your problem and the shifting situation in the middle partition wall, as well. Before I proceed, I will caution you that not to confuse the symptom of the cracking walls and poorly operating doors with the source of the issue. The pocket doors and wall construction may have little to do with the movement, which is more likely due to structural components in the basement of your home.
The main problem with these types of doors is that they are very difficult to repair if the track becomes loose within the hollow wall cavity. Repairs normally require removal of the casing, one side and the top of the door jamb, at a minimum. Often the walls require partial removal to replace the track with a better quality one, so replacement of the doors with swinging ones is not that much more work. One thing to take into consideration is the space for the newer swinging doors to operate. Pocket doors were often installed due to a lack of wall or floor space for swinging doors to operate. From this perspective, pocket doors are an extremely efficient way to maximize wall and floor usage.
From your description, I would doubt that the centre wall with the pocket doors is a load-bearing wall. This can be determined by locating the main beam or beams in the basement, which normally run directly below the load bearing walls in a home your age. If this beam and the teleposts run in the location and same direction directly under this wall, then I am wrong. If the beam runs perpendicular to this centre wall, then it is not likely load bearing, but is still susceptible to seasonal movements in the floor structure.
The reason for my doubts that this wall is load bearing is the distance required in the wall cavity for a double pocket door. For two average 30 inch pocket doors, the hollow wall opening required is four times that distance. That would translate to a 10 foot opening in the wall, which would require a substantial beam above this opening to carry the load of the floor or roof system above. This is certainly possible, but would not jive with your seasonal movements and binding of the doors. Also, there should be less cracking at the corners of the doors with a large beam to strengthen the header area. Another possibility is that the builder significantly undersized this beam with a typical double header and this is causing the shifting and cracking. This is less likely, as this second scenario would likely lead to more noticeable sagging and cracking above the door opening.
What I would suspect is that the wall in question runs perpendicular to the main beam(s), but may intersect the beam(s) over top of one or more teleposts. These teleposts are likely subject to seasonal movement in the footings below them, which causes the binding and cracking in the wall running at right angles to this movement. Again, this can be determined by locating the teleposts and beam or beams in the basement of the home.
To answer your question about strengthening the door frames, this is certainly possible if you open the walls, but may not be necessary. Another issue that may be causing this movement is basement partition walls that may be improperly installed tight to the underside of the floor joists. This was common practice in finished rec-rooms of the era your home was built. If a substantial space, or slip-joint, was not installed at the top or bottom of these interior basement walls they will almost certainly push up on the main floor, due to seasonal movement in the basement concrete floor slab. This floor slab movement often causes much more dramatic movement and cracking than the teleposts, as most people who live in older Winnipeg homes have experienced. This can be identified by looking at the top and bottom of the unfinished side of basement partition walls. If these walls are completely finished and the basement ceilings covered, it may be difficult to determine, but is more likely to be the cause.
Again, check the location of these basement walls to see if they run under the problem walls on your main floor and see if any slip joints are visible. If no space is provided, trimming these walls, followed by some slow, careful telepost adjustment may minimize this problem. In that case, removal and replacement of the pocket doors may not be a priority anymore. Care should always be taken to identify the source of problems, particularly structural movement, before attempting major repairs that may do little to solve the problems.