Detroit Metro Soap Box Derby

DMSBD Tech Tips
Brake and Steering Cable – by Ian Carsten 05-23-05

The brake and steering cables of derby cars is 1/16-inch diameter hard wire rope. It is woven of high strength, heat-treated alloy steel wire and has zinc or zinc-cadmium plating for corrosion resistance. It consists of six bundles of wires, seven wires to each bundle, woven into a rope. It is quite strong and corrosion resistant and stretches minimally under tension.

The AASBD packs two 84-inch lengths with each kit car. Replacement cables can be ordered from the AASBD by telephone or through their website. Also, 1/16-inch hard wire rope can be purchased at most well-stocked hardware stores. As long as it’s sold as “hard wire rope”, it is identical to the material sold by the AASBD and may well be from the same manufacturer.

We have seen cars show up at our mandatory pre-race inspections with steering and brake cables made of braided mild steel picture-hanging wire. It looks significantly different than hard wire rope and is very soft and weak by comparison. It cannot tolerate the normal tension brake and steering cables must endure. It stretches a great deal under tension and breaks easily. Never use picture-hanging wire. It is dangerous and illegal for derby car use.

It is important that the cut ends of brake and steering cables not have the individual wires splayed out from the cut ends. Otherwise, it’s very difficult to thread it through the cable clamps. Also, splayed cable wires are very sharp and stiff and easily poke holes in your wrists and fingers as you handle or work on your car.

To prevent this, use a proper hard wire rope cutter. These have hardened tool steel jaws that are curved to keep the cable nearly circular in cross section as the cut is made. This produces a clean cut that leaves the cable round and does not splay the wires at the cut. Don’t use straight-jawed cutters because they flatten the cable and splay out the wires of the cut ends.

1/16-inch hard wire rope is commonly used as brake and shifter cable on bicycles. The very best hard wire rope cutter we know of is the Swiss-made Felco C7. This and other less expensive cutters can be purchased at www.biketoolsetc.com. Similar tools can be found at most full-service bicycle shops.

After cutting the cable, you should splay-proof the cut ends. The AASBD recommends soldering it, but the anti rust coating of the cable prevents this. Too, the over zealous application of heat during attempted soldering, especially from a propane torch, may anneal and soften the cable, weakening the overheated area. It’s easier and safer to splay proof the ends using Loctite© Liquid Solder Filler as detailed in the article, Easy Alternative to Hot Soldering Cable Ends, elsewhere in Tech Tips.

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