Erratic Speedo - '13 V7

[zokn]

Riding my 2013 V7 Stone I hit a curb at a far clip (accident avoidance, best case scenario).This damaged both my wheels which needed replacement. The bike flopped to a stop on two flat tires, upright, but I couldn't hold it that way, and it fell fairly gently on the left side. When riding after replacing the wheels, I noticed that the speedometer needle was erratic: sometimes showing 130 km/h when the GPS showed 100; sometimes oscillating (2 times per second) + or - 15 to 20 km/hr different from GPS. Most of the time it reads significantly high as an average and oscillates. Riding at 70 km/h on the GPS will have the speedometer needle oscillating an average around 85.

From new the needle read low. A steady needle at 80 km/h would show 75 km/h on the GPS. Now it reads very high and oscillates.

After reading all the threads here, I ordered and installed a new speed sensor. Unfortunately, there is no improvement. I next removed and disassembled the gauges, looking mostly for trauma from the fall, but found nothing obvious to the eye. I checked the cables and connectors and again see nothing visually obvious.

I have used GuzziDiag to change the engine mapping, but I do not know how to use it (or even if it can be used) to check or reset the speedometer. I'm a reasonable amateur motorcycle mechanic, having owned and rebuilt BSAs and BMWs from the pre-electronic engine control era, including a seized Smiths Speedometer from the '60s.

I have disconnected the battery and left it unconnected overnight, which helped some owners with a wonky speedo, but unfortunately, not mine.

I would be grateful for further suggestions and guidance on what to try next.

My last resort is to take the bike to a dealer, but where I buy parts is 1200 kilometres from me in Montreal. There is a dealer a little closer in Quebec City, but I have no experience there and if I'm that far along, I might as well go to Montreal. I'm located near Halifax, Nova Scotia. I'm concerned that if I need to take the bike to a dealer, it may end up there all winter waiting for parts and repair and incurring winter storage charges, so a solution that I can pursue at home is more ideal.

Cheers,  Stephen

[guzzisteve]

You need to PM  Meinolf here or Beetle over at Griso Ghetto forum. May have damaged something in the dash. I would think you could find the anomaly from pins at dash connector. Service manual may give reading you need to see. I never had an issue like this.

[malik]

I would double check the speedo sensor (are there tests of this in the service manual?), it's installation, the connector block (not an uncommon source of problems) & the wiring (as thoroughly as you can) before looking at the dash or the ECU. That's the part that got whacked hardest, and also the part that suffered human intervention.  Be pedantic.

[Kiwi_Roy]

I think this is the correct schematic for your bike, it shows what looks like a Hall Effect sensor (3)
https://www.thisoldtractor.com/guzzi007/schematics/2013_V7_Series.gif
The thing about these sensors, the pulse train coming from them should be dead steady, a fixed number of pulses for every revolution of the wheel, if you could connect a 12 Volt LED to the middle wire of the sensor and chassis you would see a regular pulse coming every time a target passes the sensor and staying on when the target is present. I suspect you don't have ABS on that early model. Look at the wheel where the sensor is mounted, tell us what acts as the target is it bolt heads or a slotted wheel, a picture would be good.
The bolts need to be some ferrous material, not stainless, test it with a small magnet. Of course if it has an ABS style sensor I am talking nonsense.
Is there too much gap between the sensor and the target?
It could be a loose wire giving you additional pulses or water inside the sensor that's quite common. there are only two connections to look at, a 3 pin under the tank somewhere and another at the speedo itself 13 and 17 and the ground of course, that could possibly be loose.
Tire size has a large effect on these bikes, maybe as much as 10%, did you replace the rubber with something of a different profile?

[sib]

Here's a tip about an obscure issue on the non-ABS '13 V7's:  the bolts that fasten the front and rear brake rotors to the wheels are similar enough to interchange mechanically, but still different.  The bolts for the front disc have dimples in their heads whereas the ones for the rear (speed-sensing) disc are flat headed.  The speed sensor takes its readings from those bolt heads.  Mix the bolts up and you'll get erratic and/or inaccurate speedometer behavior.  Good luck.

[Kiwi_Roy]

Here's a tip about an obscure issue on the non-ABS '13 V7's:  the bolts that fasten the front and rear brake rotors to the wheels are similar enough to interchange mechanically, but still different.  The bolts for the front disc have dimples in their heads whereas the ones for the rear (speed-sensing) disc are flat headed.  The speed sensor takes its readings from those bolt heads.  Mix the bolts up and you'll get erratic and/or inaccurate speedometer behavior.  Good luck.

Sib has a very good point, the bolts with the dimple would give a double pulse, possibly just at certain speeds.

[zokn]

Fixed!  I was quite sure it wasn't a wiring issue, having visually inspected the wiring and connectors, but Kiwi_Roy's diagram and detailed explanation of the speed sensor operation and testing was going to be most valuable if I had to go deeper there.

However, Sib's revelation that the brake disk fastening bolts were different for a reason - one that bore directly on the speed sensor's operation - was the key. Putting all the flat-topped bolts on the rear and the dimpled ones on the front was the key. My test ride this morning showed a steady reading speedometer needle, approximately 5 or slightly more km/hr over the GPS at speeds from 70 to 110 km/h, which is what I'm used to. Many thanks, Sib.

So, here's where I went wrong. After the curb hopping adventure I had two damaged cast wheels needing replacement. That would take more than 2 months, so I took both of the wheels off the bike and removed the tires, brake disks, and air valves and inspected all those for damage, of which there was none. The parts sat around the garage while awaiting new wheels and got moved around a few times. When the new wheels arrived, I excitedly put everything back together, not realizing that the brake disk retaining bolts where different for a reason. Thus, I had 3 dimpled and 4 flat head bolts on the rear. Normally, if changing wheels, I'd do one wheel and then the other, so this bolt mixup would not happen. Of course, now that I know there is a reason the bolts are different front to back, I can keep that in mind. All my bikes but one (short term ownership) had cable driven speedometers, so sensors and new to me, but if I'd thought about it, I should have known that the sensor needed uniform magnetic elements to trigger the Hall effects.

Thanks all of you who replied; this is a great forum. Oh, and it was a lovely test ride this morning - cloudy with sunny breaks, 18°C (65°F), and lots of autumn leaf colour. Maybe my wife and I will take a sight seeing ride this afternoon.

Cheers,  Stephen