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10 THINGS YOU NEED TO KNOW ABOUT CLUTCH & THROTTLE CABLES

December 11, 2012
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(1) Components. Dirt bike control cables consist of an external housing and an inner wire that slides through it. The wire transfers force to and from the controls on the bars to components of the engine (throttle, hot-start, clutch or compression release). The housing has a threaded length adjuster and end caps (called ferrules) at the ends. Each end of the wire has a soldered-on fitting, which is usually a barrel type on dirt bikes. Some applications utilize an aluminum elbow to hold the cable at a strict bend for routing purposes.

(2) Housing. The housing consists of a semi-rigid, metallic skeleton with a vinyl inner liner and outer coating. The metallic skeleton can be constructed in different ways. A coil-wound cable means that the skeleton’s metallic strands spiral around the housing like a coil spring. A coil-wound cable is more willing to make curves and bends, but the housing is more likely to compress and bind. A longitudinally wound cable means that the structure runs straight (lengthwise) down the cable. Longitudinally wound cables aren’t as pliable, but are less prone to binding. Manufacturers take the routing of specific applications into account. As a rule, the modern four-strokes’ compact features cause more routing bends than the old two-strokes.

(3) Inner layer. The vinyl inner layer must be hard for durability and offer low-friction capabilities for the inner wire to slide on. If the liner is too hard, however, the housing won’t bend easily. Worse yet, it will transmit perceptible vibration to the control lever. The vinyl liner has natural lubrication to help the wire slide. All cables have similar vinyl (PVC) material with slight variations in hardness. The outer layer of the cable housing is sometimes coated or wrapped in a steel braid on street cruisers, but this is only cosmetic.

(4) Inner control wire. The inner control wire is made with separate steel (usually stainless steel) strands that are tightly woven together. There are different thicknesses and different coarseness of the material and weave, but the resulting wire is always very strong. The design does have one drawback:?the weave makes the wire into a serrated saw blade. Eventually, the inner control wire will saw through the nylon liner and cause metal-to-metal contact with the housing structure.

(5) Wear. If any visible portion of the inner control wire is frayed, it can cause the throttle or clutch to stick. It must be replaced. Wear on the inner nylon liner isn’t visually observable, so it’s a judgment call based on feel. Although you could purchase all the individual components of a cable and build one yourself, it’s a much better idea to simply replace the entire unit with a professionally built, certified cable. If one part of the cable is worn, the other parts probably aren’t far behind anyway.

(6) Installation. Some factories grease their cables, but most new cables are sold dry?without lubricant. It’s important to lube a new cable before use. When routing a new cable, it is best to keep it as straight as possible. Bends in the cable create drag. The best strategy is to route the new cable along the same path as the old cable. The exposed inner control wire at the ends of a cable is the most likely part to get damaged. Be gentle when assembling the throttle tube/housing and the clutch lever/perch. Make sure rubber covers are in place to block debris. Tune in the desired free-play (just a bit of wiggle) with the in-line adjusters. Double-check the cable routing by turning the bars from stop to stop. Make certain that there is still the same amount of free-play at each stop and that the cable can’t get pinched or kinked.

(7) Maintenance. Lubing cables is a commonly neglected task, but it’s important. Over time, dirt and water contaminate cables. The best method for lubing a cable is to use a purpose-built cable luber. It clamps to the end of the housing of a cable and force-feeds lube into the housing. You can also use the cable luber to flush the contaminated lube and grit with light lubricating oil. WD40 is great for reducing friction in a cable, but it coagulates and attracts dirt. A purpose-built cable lubricant is best. Motion Pro’s T-3 cables have a lubing port built right into their housings.

(8) Adjuster. Cables don’t stretch. If you have to readjust free-play, it is due to heat expansion or wear someplace else. On the clutch cable, it is possible to have three different adjusters: one in-line adjuster near each end of the cable and one built into the perch. Modern four-stokes have two throttle cables that push and pull simultaneously. From a design standpoint, it is not necessary to have two throttle cables, but this is where lawyers are more important than engineers.

(9) Cable failure. Cable failure can cause the loss of control of a vehicle, thus all cables must meet international standards for durability and strength. Cables are tested above 30,000 pounds of force and run through thousands of actuation cycles.

(10) Cable vs. hydraulic. Hydraulic systems naturally adjust and compensate for heat expansion, which can be really handy. Although hydraulic brake controls are much more accurate than cable controls, a cable-actuated clutch does allow for more precise control than a hydraulic one. With the direct mechanical connection of a cable, the clutch can be finessed more accurately. A hydraulic clutch saves the clutch plates and compensates for abuse but is more vague. Plus, cables don’t leak.

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