| The Shop > Metal Stuff |
| Making Brake cables for a Car. |
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| ParCan:
Hi All I have a small car with Cable operated drum brakes. I noticed a cable has frayed so got some new Bowden inner and outer to replace all the cables. This is the same 2mm OD outer and suitable inner I have used on Motorcycle clutch cables for years. The original adjusters and nipples were all crimped on. A skilled job requiring specialist equipment which I don't have. I have soft soldered low stress nipples before now. I have also seen Soft Soldered nipples pull off on things like Motorcycle clutches. As this is Brakes soft solder is not an option ! Silver solder is the way I decided to go with newly machined Brass Nipples (CZ121 grade) and M6 Threaded Brass rod for the adjusters. The nipples and adjusters were drilled through 2.1mm (for the 2mm steel cable) and then centre drilled. Cable was passed through and Mushroomed into the centre drill so they can't pull out. Cable and nipples/adjusters were well fluxed and warmed to a dull red. Silver solder was applied until it filled the nipple / adjuster and a nice fillet was at the bottom. A test was done by cutting one soldered adjuster to make sure it was full of solder all the way through. It was. All the flux was thoroughly washed off in hot soapy water or it will corrode the steel. Installed and adjusted everything then did the foot to the floor test. Ping and a cable broke right at the bottom of the fillet on one of the nipples. Obviously not an acceptable situation ! Does silver solder react and weaken steel brake cable ? Does soldering have another effect on the steel cable ? Did I get it to hot / not hot enough ? Any clues and ideas more than welcome. Thanks |
| Lew_Merrick_PE:
ParCan -- This is false economy! The fittings in question are designed to be swaged onto the cable. Just about any good shipyard or airport mechanic's shop will have the tools needed to swage these parts for you. My usual approach is to let them sell me the fittings (for about 2X what I could get them for through my sources) and they will generally swage things up for you for a reasonable donation to the coffee & pizza fund (I tossed $10 US into such a kitty last fall to have 8 fittings swaged onto 4 cables). The fittings ran about $10 each (being fork and clevis types). Using 3/16 inch (call it 5 mm) cable, the systems tested out to 2400 lbs proof load each. |
| ParCan:
Hi Lew. I had no intention of doing things that would not work. 2 evenings have gone into setting this group of 3 cables up. It's obvious silver soldering is not appropriate so will go buy a cable set for the car. These will be the first cables I have bought in like 30 years and my first failure at making them. Ether that or Ill find a suitable shop who can put the ends on. Thanks for your advice. |
| awemawson:
I'm guessing that heating the cable to silver soldering temperature has softened it. Presumably it would originally have been hard drawn, but the bit by the silver soldering would have been annealed. |
| vtsteam:
The solder also wicks into the cable, and up it forming an irregular hard spot internally that fatigues easily. Swaging actually causes the metal to cold flow into conformance with the outer cable, but does not wick into the cable. |
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