erratic speedo

[remfanuk]

what's the usual cause of a speedo needle flicking about and not giving a true speed reading?  frayed cable?  dodgy speedo unit? speedo drive?  can the speedo be taken apart to see any possible reason?  thanks.

[tris]

What bike matey?   

[Frenchfrog]

look at the speedo drive off the front wheel first. They are fragile and need  lubrification.The tang that catches on the wheel often gets bent or broken....a really shit design.Ducatipaddy has drives and tangs (or did ) .
Then when that all fine and dandy you can expect your speedo to be pretty inaccurate
On my T3 it was reading around 8 kph low at 50kph....lots of sneeky speedtraps wher I live so when going to town I like to stay more or less within the limit but I noticed cars building up behind before I got one of these digital ones as an add on  https://www.sigmasport.com/en/produkte/motorrad-computer/motorradcomputer/wired/mc1812moto

[moto]

what's the usual cause of a speedo needle flicking about and not giving a true speed reading?  frayed cable?  dodgy speedo unit? speedo drive?  can the speedo be taken apart to see any possible reason?  thanks.

My experience has been that the best fix is to buy new units, speedometer and tachometer, for my T3. In both cases I first tried rerouting and replacing cables, to no avail.

[remfanuk]

thanks for the replies...not been around here much.  it was for my 1979 v50 mk2. would have to look at what used tachos/speedos are out there but they could be equally buggered.  the needle doesn't so much wobble, rather oscillate wildly!!  i have tended to judge my speed by those around me...not ideal.  i could get a separate gps speedo and maintain the Italian flair that lives in my bike otherwise known as gremlins!

[pehayes]

it was for my 1979 v50 mk2.

Ah, that would be driven by a worm drive on the front axle.
Start by lubricating the drive system before it fails completely.  The top of the worm drive has a little, domed fitting.  That dome is a spring loaded steel ball.  Press the ball inward and then dribble some gear oil into the worm drive body.  If you are clever, you can attach a hose with a clamp and pump in some light grease.  The pumping action will depress the ball and allow passage of the grease.  This picture is not  your speedo drive but your's will look like this.  That very top fitting has the spring loaded ball for injecting grease or oil:

https://www.ebay.com/itm/173115169800?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=173115169800&targetid=1645685073328&device=c&mktype=&googleloc=9032008&poi=&campaignid=16730423415&mkgroupid=135815925780&rlsatarget=pla-1645685073328&abcId=9300841&merchantid=6426024&gclid=Cj0KCQiAgribBhDkARIsAASA5bvG5RH8vBGSyyzRDWOPWHMLgrVLqhG7iDUqzIm93UrwESNKDAJX51oaAoEOEALw_wcB

Secondly, remove the cable.  Perhaps extract the core from the cable body to inspect for any frayed wire.  Replace as necessary.

Thirdly, if the issue is inside the instrument it will need to be disassembled and lubricated by a professional.

Patrick Hayes
Fremont CA

[remfanuk]

Patrick that is an awesome reply...thank you.  when i get to that point of the rebuild i will do exactly what you have suggested.  absolute worst case scenario will be a gps speedo.  cheers.

[Canuck750]

You describe the wild behaviour of my old Eldorado speedo! I gave up on replacing the Veglia and installed a new Chinese eBay GPS operated speedo on my Guzzi. I recently posted a description of the work required to replace it and I am very pleased with the GPS unit, around $100 USD and easy to install.