Speedo weirdness

jchesshyre · Post by **jchesshyre** » Tue May 21, 2019 7:44 pm

On a ride yesterday I noticed my speedo behaving erratically. I was sitting at around 80 and noticed it wobbling slightly above and below 80. It wasn't doing this constantly - it would do it for about five or ten seconds then stop, then do it again after a bit.

Then I noticed that it was reacting oddly to speed changes - say when accelerating from 60 to 80 it would jump up faster than it should, overshoot 80 slightly and then settle back down. Similarly, when braking it fell much more quickly and further than it should, then jumped up to the correct speed.

All of the above was intermittent.

Is there anything other than a faulty speed sensor that could be causing this? All other instruments are fine.

Kev L · Post by **Kev L** » Tue May 21, 2019 7:54 pm

Check your battery terminals as well. When loose they can cause similar issues.

jchesshyre · Post by **jchesshyre** » Tue May 21, 2019 8:59 pm

Kev L wrote: ↑Tue May 21, 2019 7:54 pm Check your battery terminals as well. When loose they can cause similar issues.

Bingo. Cheers! I recently installed relays for my headlight (big improvement) and the battery negative terminal was slightly loose.

I have a fair understanding of the theory of electrical systems but am fairly lacking in practical knowledge! Why would this looseness affect the speedo and nothing else?

tony.mon · Post by **tony.mon** » Tue May 21, 2019 9:46 pm

Because pretty much everything else earths through the frame, but the clocks are on insulating washer mounts.

jchesshyre · Post by **jchesshyre** » Tue May 21, 2019 10:07 pm

tony.mon wrote: ↑Tue May 21, 2019 9:46 pm Because pretty much everything else earths through the frame, but the clocks are on insulating washer mounts.

Pete.L · Post by **Pete.L** » Wed May 22, 2019 2:17 pm

Phew!
Nothing worse than having wonky speedo’s
I’m glad that’s sorted and you haven’t been left in a bind

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Kev L · Post by **Kev L** » Wed May 22, 2019 7:42 pm

You’re only upset because the ‘S’ came off of yours!!!

Pete.L · Post by **Pete.L** » Thu May 23, 2019 7:24 am

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jchesshyre · Post by **jchesshyre** » Tue Jun 18, 2019 9:46 pm

Annoyingly this has come back. It did it the other day so I checked the battery terminals again, and although not loose they weren't absolutely tight as a [insert dirty simile] either so I tightened them with a spanner instead of the screwdriver I'd used before. Problem went away again.

But it's just done it again, and I checked the terminals and they're totally tight.

It's only really above 50 or 60 mph, and is worse the higher the speed and/or acceleration.

Could a R/R or battery on its way out do this? My R/R is finned but is a Ducati one (was on the bike when I got it three years / 60,000 miles ago).

That said (and of course this could be coincidence) it has only shown up since I installed headlight relays. I'm really quite sure I did all the connections well but is there a way that some part of this circuit (battery->relays->headlight or battery->headlight switch->relays->headlight) could be causing this? There's no flickering or anything from the headlight which I'd expect there to be if my wiring was at fault.

Wicky · Post by **Wicky** » Tue Jun 18, 2019 10:31 pm

Check the connector where the speedo sensor plugs into the loom by your right leg. It can be an early warning that R/R or sensor itself is on the way out.

tony.mon · Post by **tony.mon** » Wed Jun 19, 2019 12:06 pm

Also check the earth strap is tight.
The connections at the rear of the cluster are often corroded, and it's worth checking those as well.

jchesshyre · Post by **jchesshyre** » Wed Jun 19, 2019 1:37 pm

tony.mon wrote: ↑Wed Jun 19, 2019 12:06 pm Also check the earth strap is tight.

Is that the one on the thermostat?

tony.mon · Post by **tony.mon** » Thu Jun 20, 2019 9:27 am

No, the big thick one that runs to the back of the engine and fits via one of the speedo sensor bolts just in front of the shock and beside the rear CCT.

jchesshyre · Post by **jchesshyre** » Tue Aug 20, 2019 9:17 am

Hmmm, this issue is still ongoing. I've checked the points mentioned above. The odd thing is it's very intermittent. A lot of the time it's not there, then my speedo will decide to start going crazy. But it only seems funny above about 60 mph. The other day I was sitting at 80 and it was waving between 60 and 100 on the speedo. I pulled over to look at the battery connections, the speedo sensor connections, and the earth connection by the sensor and couldn't see anything amiss. The problem then didn't show again for the remaining hour of my ride.

Other times it's not as dramatic and just shows slightly odd response to changes in speed (both braking and accelerating) - changing a bit too quickly, overshooting the speed reached before returning to showing the correct speed, etc...

It *could* be a dodgy speedo sensor but I replaced it a while ago - yes it was a good couple of years ago but would it be expected to fail again after this time? When it failed before it was just intermittently not working at all, none of this behaviour.

jchesshyre · Post by **jchesshyre** » Tue Sep 10, 2019 10:59 pm

Update: turns out it was the speedo sensor.

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