“Old Bill”

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The first time I took Old Bill out on a trail, we hit some twisty parts right off the bat. This was my first taste of clutch binding. Fortunately, it wasn’t in a bad situation, but it was enough to get my attention. I’d seen the roller chain clutch linkage by Advanced Adaptors, and had seen that others had made their own, so I decided to give it a shot. Here’s the how and why of what I did, and what I ended up with. Credit goes to John Wickersham for the new connecting rod idea.

A simple method for bending thicker pieces

The first thing was to bend a piece of 3/16″ cold roll to approximately 45. A sheet metal brake is not heavy enough, and bending in the vice is crude and inaccurate. I used an old shift rail from the T90, and clamped 2 pieces of angle together. After that, it was a simple matter to line it all up and work the press. Very controlled.

Heim Joints

These are called Heim joints. AKA ball joint rod ends. I picked these up at my local bearing supply. If your bearing supply doesn’t have them, look for places that stock roller chain. Basically, these allow some twist while still allowing a push or pull. The alignment doesn’t have to be exact, or even static, they move to compensate. Perfect for when you’re on a chassis twisting trail.

First attempt

Yes, I’m jumping ahead fast, but this is what I ended up with. One sprocket simply did not allow for the alignment to be a straight pull. All the angle that I would have ended up with adds to the amount of force necessary to push the clutch in. Simply adding the extra sprocket allowed me to align everything to be a straight pull. HOWEVER….the 3/16″ plate flexed with the extra leverage induced by the top sprocket. Even the frame rail was flexing with this set up. The pedal felt “spongy” and wasn’t smooth. While the engineering was solid, the mechanism wasn’t. I had considered going with a 1/4″ piece, but that would have only served to flex the chassis more without extra reinforcement that took the whole project out of my KISS design method.

The new idea

After doing some thinking and research, I came up with a simpler idea. The main thing that “binds” is the connecting rod between the tab on the clutch pedal, and the tab on the clutch bell crank. When they are worn, of course, there is enough room for them to move freely, or at least, more so, than when new. When the frame twists some, this piece binds in the holes in the tabs. So instead of the stock connecting rod, I made a new one with Heim joints on both ends. This allows for slight misalignments when the frame flexes some. I used 5/16″ grade 8’s with metal locking nuts to secure them to the tabs with no extra drilling necessary. The only difficult part was running the thread on the rod to mount the female ended Heim joints.

Worked very smoothly

The bell crank can bind somewhat as well, but the opinions I’ve heard are that if you take care to center it well, and replace any worn pieces, it’ll work smoothly in all but the most extreme situations. The connecting rod “rotates” quite freely when there is no tension, and is even movable with effort when under the full force of the depressed clutch pedal. It’ll seek it’s own center depending on the alignment between the 2 mounting tabs. My first impression of this set up was very good. The clutch action was MUCH smoother and MUCH less spongy than the chain linkage shown above. The strange creaks and groans are gone, as is that “gritty” feel that the original set up had. All you need are 2 Heim joints, some nuts and bolts, a length of 5/16″ rod, a 5/16″x24 die, a hacksaw, and a couple hours. Well worth the effort I must say.

Thanks Thad for the write up!