Speedometer Cables

Speedometer Cables

As a leading manufacture of Speedometer and Tachometer cables and other flexible drive shafts, Speedograph Richfield take great care during the manufacturing of the raw materials, components and complete cable assemblies, to ensure that the finished product is produced to the highest standards.

We have many years of experience in supplying both large volume and small quantity requirements, and offer the following installation information, which we hope you may find useful.

It is helpful if you consider a speedometer or tachometer cable to be a flexible rotating shaft within an outer conduit or casing.

The inner shafting is constructed from a number of fine wires, precision wound in opposing directions. After winding, the shafting is heat treated and stabilised, and it is not possible to return the individual wires to the original state they were in during manufacture..

After winding, and during assembly, we apply preservative and lubricant to the inner shaft, and this is usually sufficient for the lifetime of the assembly. If however you feel that some lubrication is necessary, you should NEVER use lubricating oil. If you do, it will almost certainly be wound up by the rotating inner shaft, acting as a screw, and forced into the instrument, causing serious if not permanent damage to the instrument. The only lubricant we recommend is Shell SB2628 GREASE., which should be lightly applied to the inner shafting, and the top few inches wiped clean, again to avoid any possibility of this being wound into the instrument.

During the normal life of the flexible drive assembly, the inner shaft rotates many millions of times, at a relatively high speed, and if correctly installed should give years of service Over a number of years, and depending on the length of the cable assembly and the torque requirements of the instrument, some of the rigidity of the inner shafting will be lost, often resulting in a wavering instrument needle. The only cure for this is to replace the complete flexible drive assembly.

Speedometer and tachometer cables should ALWAYS be fitted as complete assemblies

During manufacture of a cable assembly, the inner shafting, outer casing and fittings are all matched together, and if you attempt to fit a new inner cable into another outer casing, disaster will almost always result. For example, if you have a broken inner cable, consider “WHY has it broken ?”. It is almost certainly due to either the instrument seizing, or the incorrect installation of the cable assembly with tight bends or kinks.

In either event, fitting a new inner cable will not cure the problem, and if for example, the new inner shaft is only millimetres longer than the original, it could put internal pressure on the instrument drive, and permanently damage the instrument.

If the inner cable has been damaged by a seized instrument, or a kink in the outer cable casing, it will only fail again. It is also likely that a small portion of the broken inner shaft has been left in the outer casing, again causing premature failure.

We hope this explains why only complete assemblies should be fitted.

When fitting a new assembly, consider first of all why the old one has failed.

The first thing to do is to make certain the instrument is running freely, and this can easily be done by firstly connecting the new cable assembly to the instrument only and lightly attempting to spin the cable by hand from the other end; If it does not spin freely, have the instrument serviced before fitting the cable.

You should also consider carefully the routing of the new cable, so as to avoid any sharp bends. The minimum normal radius you should aim for is 6” or 150mm, and there should be no bend within 2” to 3” of either of the end connections.

If you cannot achieve these basic requirements with the cable you have, do not install the cable, but consider; a new route; a longer or shorter cable; or the fitting of a right-angle miniature gearbox. Speedograph Richfield can custom-make a new cable assembly to the new length you require, and we also offer a range of right-angle gear-boxes.

Almost all speedometer and tachometer flexible drive cables are fitted with knurled fixing nuts, and this is to prevent over-tightening with a spanner or wrench. All nuts should be fitted to hand tightness only.

These simple precautions should help to ensure that you get the maximum service from your Speedograph-Richfield flexible drive shaft assembly.

Service Information for Flexible Drives