Hi Fred,

Tracking mechanisms can be tricky...... It sounds to me like there is a leak in a signal line leading to a pouch. Or, a pouch isn't dished deep enough, which prevents the valve from seating. You might also have a leaky valve. Obviously, if there are any leaks in the pouches or valves, the mechanism cannot work correctly.... It is imperative that the valve block and bellows be 100% air-tight. The slightest leak will cause the device to malfunction.

I've repaired numerous tracking devices without replacing the gaskets. However, they are always replaced when the device gets rebuilt.

I will assume that you checked the bleeds and that they are clean. I will also assume that you checked the air-tightness of both bellows before attaching them to the valve block.

Also, you can check the operation of the valve block before you put the bellows back on. The process is a little difficult to put into words. You have to understand how the block works. Basically, you open and close the signal ports leading to the valves as would happen when the paper opens and closes the ports, and you see how the device responds. (See page 27 of the Service Manual for proper valve clearance and cleaning.)

One of the reasons I haven't attempted to create a webpage about testing, repairing, and rebuilding a tracker mechanism is that for starters there are four basic types. Those four basic types are then sub-divided into various smaller groups that have slight design differences. Explaining how each one operates and how to rebuild and test them would likely fill a small book.

If it's of any help, the four-hole tracker device is something like two and-or circuits in transistor theory. When the two inside holes are closed, the two outside holes control the bellows. When both outside holes are open, the two inside holes control the bellows. In other words, opening the two outside holes changes the state of the associated valves and turns control of the bellows over to the other two valves. You can watch this happen. When all four holes are closed, both primary (or outside) valves are closed, and vacuum is applied equally to both bellows, keeping them centered. As one outside hole on the trackerbar opens (right or left), this opens (or activates) the associated valve and it changes state. This turns OFF the vacuum to one bellows, causing the other to draw further IN (or collapse), which adjusts the position of the music roll. In the condition when both outside holes are open, both primary valves are activated (or UP), and an equal amount of vacuum is applied to both bellows via the secondary valves. As one of them gets activated, by opening a hole on the trackerbar, it TURNS OFF the associated Primary Valve, which in turn shuts off the vacuum to the associated bellows and allows the other bellows to collapse, adjusting the position of the roll.

It goes without saying that the four-hole tracking device is the most complex device in any regular 88-note player piano. Getting a grasp of the theory of operation is somewhat difficult since it is kind of backwards compared to other pneumatic devices, i.e., when it's Off, it applies vacuum to the bellows.

Hope this helps.... I'll send you a piece of leather for the pouches. The cork gasket material should work well as long as it compresses slightly. If it won't compress, then it might leak a tiny amount, which will cause a problem. The gasket must compress to handle any slight irregularities in the wood. BTW, the cloth cover is basically there to create an air-tight seal over that part of the block. However, if it is glued on with hide glue, it can be relatively easily removed to access the air channels for cleaning. Occasionally, a bleed will get very clogged such that the trackerbar pump can't clear the bleed. In such cases, the cloth can be removed and the bleed cleaned manually.

Musically,