Other Stuff > Misc / Open
Why might my speedo be failing?
Bryanj:
The easy answer is just like me old age and infirmity!!
I have seen cables where the inner is a bit short and does not engage the square in speedo properly, i have also seen some drive plates, usually on 550, where they are made in two parts and rubber bonded together presumably for damping and the bonding has let go, early ones are one piece steel and dont do that.
Otherwise as said the drive gearbox could be failing or the speedo itself, the pencil is an idea but most of us now have a least one battery drill that will go backwards!
exvalvesetdabbler:
The snail or worm drive is usually well greased and it can go hard and gum things a bit. When I have refurbed one in the past I have washed out all of the old grease with a solvent, while spinning it around, dried it out and packed in a bit of fresh grease.
On the 400 drives that I have the coupling is two metal parts bonded with rubber, if the `snail` seizes up it can rip the rubber bonding.
Regards
Dave
exvalvesetdabbler:
Or connect the taco cable to the Speedo
4000 engine rpm with 7:1 drive ratio = 571 rpm on the tacho cable
60 x 571/2240 = 15 mph reading on the Speedo.
Dave
Athame57:
--- Quote from: exvalvesetdabbler on June 13, 2026, 06:55:41 PM ---Or connect the taco cable to the Speedo
4000 engine rpm with 7:1 drive ratio = 571 rpm on the tacho cable
60 x 571/2240 = 15 mph reading on the Speedo.
Dave
--- End quote ---
I'll definitely try that one out Dave! ;D
Athame57:
It really looks like I had fitted the broken cable on instead of the new new one :o and put the good one to one side. A correction of that has my speedo up and running again, but not before I'd already started searching the web for rarish spare parts. Senior moment ::)
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