British Motorcycle Cable Help and Advice
- Measuring and Purchasing Cables
- My Commando clutch is slipping or is so stiff that the cable keeps breaking
- Fitting twin leading shoe front brake to an Atlas, the cable won’t reach
Measuring and Purchasing Cables
As previously mentioned, the relative difference in length between the inner wire and the outer cover is what’s important for the cable to function. The overall length of the cable can be varied to suit the type of application but the relative lengths of the inner and outer wire will be the same for the same bike with clip ons or ape hangers. People with Triumphs often order for example BSA cables because the length sound like it would suit their purpose better and then complain when they don’t work. In general terms most Triumphs used mid adjusters in their throttle and choke cables. Pretty well all Nortons had adjusters in the tops of the carbs for which the lower cables (from the junction boxes) did not need to have adjusters in them. This all again comes back to relative lengths so if for example if Triumph has adjusters it’s a pretty good bet the previous owner replaced the carbs with ones with the wrong tops.
My Commando clutch is slipping or is so stiff that the cable keeps breaking
We get asked questions about setting up the Commando clutch on an almost daily basis. While I don’t want to get into a detailed analysis, it is important that the basic operating principles are understood. Armed with this information it is much easier to set it up to operate efficiently.
At least three different types of plates (of varying thickness) were used 1968-77 and several different pressure plates were used in order to achieve the optimum total clutch pack thickness. We recommend, on the advice of Norvil Motors, that 4 Surflex fiber plates be used. There are claims that some other makes of fiber plates can “grab” and cause the mainshaft to bend.
The essential principle is that the spring exerts its greatest pressure when it bears no load and the flatter it is the weaker the pressure becomes. According to Norvil the spring rarely if ever gives any trouble and replacing it is unlikely to cure clutch slip. What you have to ensure is that the total thickness of your clutch pack, including the pressure plate, is right. If the pack is too thick the spring will be too flat and the clutch will slip. If it is too thin, operation will be heavy creating all sorts of problems.
Another point to note is that the operating lever in the outer transmission cover differs between that fitted in the transmissions of the earlier Norton & Matchless machines from that used in the Commando. The pre-Commando machines used a conventional clutch with pre-loaded springs. With this type of clutch the further you pull in the lever, the stronger the spring pressure becomes. With the Commando, the spring pressure becomes progressively lighter as you pull in the lever. The cam surfaces of the two types of release levers are therefore ground differently to provide the best operation and we often find the wrong one has been fitted.
Most of the problems have been caused over the years by various owners mixing and matching incompatible parts. What you want to achieve is a pack the thickness of which is such that the spring is flat enough to be light in operation but dished enough to grip properly. Several ways to achieve that are fitting a different pressure, reducing the thickness of the existing one by machining the face, shimming behind the back plate or fitting an extra steel plate.
Well set up it is a beautiful clutch but a bad one is an absolute pig.
Fitting twin leading shoe front brake to an Atlas, the cable won’t reach
Completely different cables. Pretty well all Nortons (and Matchless/AJS for that matter) before the Commando didn’t have adjusters on the levers. Adjuster screwed into the gearbox for the clutch and was on the brake plate for the Atlas etc. Commandos used levers with adjusters in them so free cable length was different. The critical thing for all cables is the relative difference between the inner cable and the outer cover.