Speedometer Problems

[TANGO7]

What is the likely cause of a speedo reading ok up to 40mph then sticking at this speed and notreading speeds any higher, combined with the odometer not registering.

Is it likely to be the instrument itself or the drive mechanism?

[Jonathan Kay]

What sort is it: mechanical drive from the gearbox, electronic drive from the gearbox, electronic drive from a rear wheel?

All other instruments OK?

Jonathan

[TANGO7]

Mechanical drive from gearbox. All other instruments OK.

[Jonathan Kay]

I don't know the best way to localise the fault. 

I'd start with inspecting the output and angle drive at the gearbox and looking for looseness and general wear. There's a very recent thread where I posted an exploded diagram... but I can't find it.

In that same thread there's a mention of putting a drill on the gearbox end of the cable and seeing what happens. But I haven't done that since about 1973 and can't remember the details.

Speedometers are surprisingly repairable.

Jonathan

[Alastair B]

Quill drive from gearbox could be damaged to make consistent readings unreliable is most likely, then Speedo drive cable most likely next culprit, then the small 90 degree transfer gearbox and finally the instrument....these are probably in the order of cost as well, good luck

[7 wonders of the world]

drop the cable at the gearbox and and using a drill spin it up you can see what the problem area is then,

[Jonathan Kay]

Any hints or precautions for the drill trick? Possibly something like:

• Get the cable run as straight as possible for the first tests.
• Fit the inner to the chuck.
• Hold the outer... by hand?
• Start slow?

Jonathan