Speedometer issues (inaccurate speedo) ??aftermarket brake disk

Hi all, I'm completely new to Moto Guzzi, always wanted one and have just picked up a 2010 GRiSO, Woohoo!

Since taking delivery though I've been a bit suspicious of the speedo, I took it for its first big ride and sure enough it was reading low... I've since ridden with a GPS speedo alongside and it's actually reading between half and 2/3 of my actual road speed, and is also a bit sluggish/erratic. It's affected all the way through the speed range.

I've seen a few threads on speedo sensor failure but none that presented like this so I thought I'd ask whether anyone has had the same problem, but also document the fix.

The speedo sensor doesn't look like it's in good order, there's a few pinholes in the cable, by the little grommet the holds it in; I'll try that first, just talking the the (Triumph) dealer that I bought it from to see how much they're willing to pay for.

Incidentally, the last thing they did before sending it out was replace the rear brake disc; it doesn't look like the stock one, it has a solid ring around the inside, incorporating the fixing holes where the stock one seems to just have the holes branching off the main disk... has anyone got an aftermarket one fitted? Any issues? I'm not really up on how the sensor reads the speed or whether that would interfere.

Any advice would be really, really appreciated. I work for the emergency services so my licence, and therefore my speed is really important to me! Cheers!

I believe the sensor reads the disc fixing screws. The ring might be interfering. Also make sure all the screws are there and they're steel.

Yeah. I was thinking along those lines. Can we have a pic of the wheel with disc off the bike so I can gurn and compare?

Thanks for the replies, I'm afraid that I can't get the rear wheel off the ground (yet!) I've only had the bike a fortnight and wasn't anticipating any maintenance... I'm going to order a service stand today.

This is also stopping me working on the sensor... the ring blocks access to the screws.

I don't know if this helps...


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Hmmm. Let me look at a wheel tomorrow......

I couldn't help it, i needed to go and take a look, i can see the holes and therefore the bolts make for easier counting, but most of all i noticed how bloody dirty the bike is!

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That's not dirty, you should see my bike Keith. Mine gets ridden every day in all sorts of weather. I think I've cleaned it 3 times since new and Pete has cleaned it after a service once, back in 2013. I just ride the thing, I don't care how clean it is, but that's me.

From memory there are 6 disc bolts, my money's on 1 or 2 of those bolts have been replaced with non-ferrous (stainless steel) bolts. Hall (magnetic) speed sensor only works off mild steel triggers.

Could it also be somebody has been inside ecu via guzzidiag etc and messed with speedo calculation formula.

Oh, I hope your back wheel studs are not loose!

Thanks for the advice so far, I'm about to start a run of shifts so probably won't get a proper look at it until next week but centre stand is on order, the dealer has agreed to post me a new speedo sensor (350miles away... it'll have to be very broken before I send it back) so hopefully try a few things on my next day off

Problem solved!

I think we were all a bit suspicious of the rear disc so I ran it up the road without (not recommending this...) and it worked perfectly, swapped out the disc and I've got a speedo that reads within 1-2mph of the GPS right through to national speed limit.

The offending object (pictured) was an EBC offering so can't really blame the dealership; I've bought loads of EBC stuff without fault so im a little surprised, not as surprised as when I started looking for an OEM one though... would love some advice on where people are getting their parts in the UK.

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Check the disc with a magnet for us 88, that one has an inner support ring, in close proximity to the pick-up must be negating the bolt heads being counted ???

Rear disc Part # GU05635730 is the same for all CARC models, just in case anyone else is looking....

If you need a genuine disc I have several of them off munters I've wrecked out. Postage to the UK wouldn't be much I don't think, it probably weighs about as much as one of my V11 sloppage sheets and they cost $30-35 to ship.

Pete

Thanks Pete, I've sourced a used one for now, I was just a bit taken aback by the lack of availability on parts that I'd consider consumables... been spoiled by my Guzzi's Japanese predecessors methinks, I'm sure that I'll figure out the suppliers soon enough

Thanks also for the part number; i find the interchangeability reassuring, I haven't just bought something that I'm going to find impossible to replace anything on!

I'm fairly convinced that the problem does lie with the inner ring, I haven't had a chance to check it with a magnet yet but on taking the wheel off I could clearly see the ring cutting across the sensor. I ran the bike with the disc off and the bolts in (none of which looked new or different) which cured the issue, running a disc without the inner ring seems to confirm it.

I'll add the EBC part number to my post tomorrow, just in case anyone is looking for (or looking to avoid) an aftermarket disc... I wonder if EBC know about the speedo issue?..

First measure the thickness of the two discs at the mounting points, if they are the same;
Cut out the inner ring between the bolt holes.
Send before and after photos to EBC.

Crazy88 wrote:

would love some advice on where people are getting their parts in the UK.

Try Gutsibits