Very odd behaviour from speedo sender

[Pete.]

Last week my speedo started giving variable readings, which reduced until eventually all I was getting was the odd flick on the needle. If I revved te bike (whilst moving, clutch in) it would jump momentarily as if affected by vibration. So I got it in the workshop and looked for the cause. I was aware of the broken wire problem but could find no issue with that,so I pulled out the sensorto clean it. Put it back in and no change.

I did these checks:

Put the bike on the mainstand, 1st gear - nothing. Revved the bike in gear - needle jumps a bit.
Revved the bike with the sender un-plugged - needle didn't move.
Pulled the sender out, ran bike in gear on the stand and held the sender close to the disc - speedo reads a steady 40mph.

So the sender works and the wiring is good, and this is where I am now at: if I fix the sender properly into the hub the speedo doesn't work, but if I pull it out a couple of mm it shows asteady 10mph idling in 2nd. Right now I have slipped a 2mm o-ring over the sender and bolted it up and it seems to be working.

Only other relevant info is that I can see the castle-wheel in the hole, and it appears clean, no metal or bits stuck to it (and in fact the sender was pretty clean). This castle-wheel is free to turn independantly of the wheel hub, but it has some drag. In other words I can turn it with a flat screwdriver but it'll hold position otherwise. Not sure if this is nomal or not.

What do you guys think?

Pete.

[Paul]

Hi Pete,

Take a look at the wires by the fuse box under the front fairing just below your clutch lever. You're looking for tell tale blue discolouration where the insulation on the wires has rubbed through and the copper wires are oxidising. You will need to remove the fairing on that side to see any damage.

Good luck with the trouble shooting.

Cheers,

Paul

[Pete.]

Got the 25 miles into work today with the speedo reading perfectly. This is with the sender spaced up with a rubber o-ring. Can't imagine why it would suddenly need more air gap but all the time e it's working fine I'm going to leave it alone.

[slparry]

Got the 25 miles into work today with the speedo reading perfectly. This is with the sender spaced up with a rubber o-ring. Can't imagine why it would suddenly need more air gap but all the time e it's working fine I'm going to leave it alone.

damaged wire being held in "place" better in the higher position?

[Paul]

Take a look at this posting from the dim and distant past. All number of electrical problems have been caused by wires rubbing through by the left hand fuse box. All it takes is to whip of the side panel and take a look, for peace of mind.

Hope this helps

Paul

[Turbonutters]

Hi.
I am new around here so hope I am not out of line.
The castle wheel should not turn independently from the wheel.
The 2mm spacing probably helps because the castle wheel got caught on the pickup.

[Pete.]

Thanks for the replies, I'll keep you all updated and check the wiring under the front fairing.

Anyone know how the trigger wheel is fitted to the hub?

[nab 301]

Hi.
I am new around here so hope I am not out of line.
The castle wheel should not turn independently from the wheel.
The 2mm spacing probably helps because the castle wheel got caught on the pickup.

Anyone know how the trigger wheel is fitted to the hub?

I've just checked my spare ( needing repair) bevel box and the castle speedo sensor wheel is obviously not spinning independently . I can't find any photos but I think it's just pressed on . Some models of bmw bike (GS) / bevel box don't use that system and looking at you tube repair videos the castle wheel isn't fitted to them.

[Pete.]

Anyone know how the trigger wheel is fitted to the hub?

I've just checked my spare ( needing repair) bevel box and the castle speedo sensor wheel is obviously not spinning independently . I can't find any photos but I think it's just pressed on . Some models of bmw bike (GS) / bevel box don't use that system and looking at you tube repair videos the castle wheel isn't fitted to them.

Cheers.

Mine isn't free to spin but I can push it around easily with a screwdriver. I figured it should be a press fit, I wouldn't call it that exactly.

[Turbonutters]

If I remember correctly it is press-fit. Solid on my bike.

[Pete.]

I've come to the conclusion that it was simply the cold weather. When the original fault appeared it was very cold, and I leave early in the morning. A few times since it has had a bit of a glitch in the early morning but been fine after 5-10 miles. Now the weather has warmed up it's working perfectly and the ring is once again snug on the hub. I guess it was just the ally hub shrinking in the cold and allowing the steel ring to slip a bit.

[Pete.]

Well, as if to spite me for thinking I had sussed it the thing started messing about again this week, so today I have pulled the guts out of the bevel box. The sender ring was not a snug enough fit so I popped it off the seat, degreased everything, went around the seat putting a ring of centre-punch marks then a smear of red loctite. I had to tap the ring back on witha drift so I know it's nice and tight now I'll never have to worry about it again.

Another good thing about it is that I got to have a good look around inside the box and I must say it'sin fantastic condition for a bike that just turned 60k miles. No metal bits, no sign of wear on the gears and the bearings are lovely and tight.

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