'Jumping / Bouncing' Speedo - Ideas on fix please

Hi All,

I have a '81 KZ440 Ltd with a speedo issue - the cable snapped a week ago so got a new one and fitted it with no issues, and started riding the bike with a steady climb on speed - until i hit 55mph then the needle started flicking and after a mile or so then shot up to pegging the needle to a point of it bouncing past the pin and is now stuck on the wrong side showing i'm doing 87 mph when stationary!

I know how to open the speedo and return the needle to the right side, but i am at a loss as to why this happened - any ideas??

Simon

That doesn't really make any sense. 
The cable is just a drive mechanism between the gear drive on the front wheel and the clock. 
Just replacing the cable shouldn't affect either end unit. 
Out the box thinking is that if the cable inner is too long and tightening it up has forced the magnet drive in the clock up and the magnet is now touching the foot plate on the needle spindle so it no longer is a magnetic drive but is effectively direct drive with a bit of slippage hence the bouncing. 
It would also explain why the needle no longer returns to zero. 
I can't really think of any other way your symptoms could be achieved. 
Think you'll need to dismantle the speedo. The magnet drive is inside the silver dome towards the bottom.

Sounds like a broken spring. 

SWest wrote:

Sounds like a broken spring. 

Be a coincidence if the return spring broke at the same time as the cable replacement Steve, but whatever it looks like time to open the guage up. 

I've had it happen. The bouncing could be a precursor to this and a binding cable the cause. I'd get a KZ650 gauge and drive for it to get rid of that 80MPH thing. 

Can the oil cylinder be refilled, and if to, what type oil?  

Yes they can, use a syringe, the cylinder top cap is thin rubber that a syringe will go through. I've found light machine oil, like sewing machine oil, works best. 

Hi All,

Thank you for the ideas / info - it's now sorted!

After dismantling the speedo i could not see any issues with the mechanism but reset the needle back to the right side of the peg and gave it a good oiling and cleaned the inside of the glass.  I took note of Warren's comment on the inner being too long and so i put a rubber spacer between the outer 'nut' and the shaft input to keep it fixed but a little away from the magnet and seems to be working great. 

Again thanks all

Simon