Slingerland Tympani Clutch Replacement - 6/7/13

These are pictures from an old Slingerland tympani that came into the shop with the entire clutch assembly missing. The pedal was there, and the clutch shaft was there, but nothing else. Without the clutch, the drum couldn't be tuned, and a tympani that can't be tuned is pretty much just a big expensive tom.

I was able to track down a clutch assembly from Falls Percussion in New Jersey, and with a few additions on my part was able to install it and get the drum back in working order.

In the center left of this photo, you can see the clutch box bolted onto the frame of the pedal. Going through the clutch box is the clutch shaft on which the box slides. Inside the box are two cylindrical pieces of steel with a ring of ball bearings between them. A spring at the top of the box pushes down on the upper cylinder, which causes the bearings to press against the lower cylinder and jam up the shaft in the box. This is what allows the clutch to hold its position and keep the drum at pitch. When the pedal is depressed, a connecting rod (visible in the next picture), pulls against a y-shaped release lever (partially obscured by the frame near the center of the picture. It's held in place with the two screws next to the big bolt). This causes the release lever to push up on the lower cylinder in the clutch, pushing the bearings up (which also raises the upper cylinder and compresses the spring), and releasing the pressure on the rod. Then the clutch box can freely move up and down on the rod until the desired pitch is reached, at which point you release the pedal and the clutch locks again.

This is the connecting rod, running from the bottom of the pedal to the clutch release lever. It has a spring on it, but only to take up slack.

I had to make the connecting rod, which was basically just a 10-32 machine screw, tapered a little bit at the head and sheathed in that long spring. I also needed to modify the bolts that hold the box onto the frame. They thread into the frame with 3/16-24 threads, but at the end of each bolt there has to be a much narrower, unthreaded section that fits into a socket on the clutch box. That modification mostly involved filing material away until the bolt fit that socket.

The mechanism is a bit antiquated, but it's also beautifully simple. There are no counter springs - when the pedal is released, the tension of the drum head pulls the pedal up. When the pedal is pressed down, it's pulling directly on the head tension rods to raise the pitch of the head. As the head gets older and loses some of its springiness things becomes a little more sluggish, but as long as it's cared for it seems like a very effective tuning mechanism. Finding parts for it, unfortunately, is a bitch, but I'll always check with Falls Percussion in the future.