Motorcycle Repair: Honda Motorcycle Speedometer, honda cm 400, speedo gears

Question
I recently replaced a broken speedometer cable on my 1980 Honda CM 400 T, OEM broke.

Odometer now working fine speedometer is very erratic.

It seems that the speedometer housing is designed to not be opened.

Is it a good idea or a bad idea to randomly spray WD-40 into the speedometer?

Answer
Hi Ted,

Bad idea to spray wd40 inside the speedo. It might cloud up the lens and
be unreadable.

The problem might be inside the front wheel speedo drive gears.
There is a worm drive that is on the wheel or axle
and it can get very stiff with age due to old grease.

First check that your new cable is turning freely
when disconnected. Then remove the wheel and the
speedo drive and make sure the gears look good and
are not full of old stiff grease or dirt.

If the speedo unit is faulty it will need replacement as they
are not easy to get apart or to repair.

If the speedo gears or cable is stiff the speedo will
read erratically.

WS
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