Why might my speedo be failing?

[Athame57]

A couple of weeks ago my speedo stopped. Time for a new cable I thinks, so I got one on fleabay. After fitting all was well a few hours, and it stops again. I figured I had bought a naff one, but also observed my routing wasn't very good.
Okay, so I get another speedo from a different source and went to change them over but couldn't find anything wrong with the one I'd just taken off. Fit new one anyway and all was well for a few hours and zunk, it stops again. I take off cable, check it and refit but nothing.  Any ideas what might be happening?

[Oddjob]

Speedo drive gears stripped?

Speedo drive not engaged onto drive plate properly?

Second is more likely. Take off the front wheel, pull the spindle out and check the drive engages on the tabs of the drive plate. If it's been like that for a while expect some damage, may be bad, may be just some scraping.

[exvalvesetdabbler]

Is the inner part of the cable  still in one piece? It should just pull out from the front wheel end.  Other than that is the inner too short and not engaging in the Speedo properly.

Also if you whittle down a pencil or round bit of wood with a square end  to fit in the Speedo and spin it anticlockwise the needle should respond.

Regards
Dave

[exvalvesetdabbler]

Check that the rubber bonded coupling hasn't disintegrated 182 in the image below.

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For the drive gearbox , 184, you will see two pegs inside just below the seal, you should be able to spin/push that round with a small screwdriver or 3m. Drill bit. Should be smooth and the flat blade that engages with the cable should rotate with it.

Regards
Dave

[Athame57]

Thanks for the answers guys. I have notice the snail has a lot of grease around it's lower parts, unusual. 

[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]

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

I'll definitely try that one out Dave! 

[Athame57]

It really looks like I had fitted the broken cable on instead of the new new one    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

[Bryanj]

Been there, done that

[exvalvesetdabbler]

Good job you hadn't tossed it in the bin and the bin men had already been down your streer

[Athame57]

Good job you hadn't tossed it in the bin and the bin men had already been down your streer

SSSHHH.... It's only been a week since I accidently threw out six nicotine replacement patches.    I'll be putting my dog in the bin at this rate. 

[Bryanj]

You mean your dog doesnt raid the bin anyway?

[Oddjob]

Sorry George but how could your speedo start working again for a few hours if the inner cable was broke because you refitted the old cable. Something else going on. Either that or you really are losing your marbles 😀😀