Speedo needle bouncing up and down

[wilhets]

Hi,
I've got an ETS that I got back on the road recently and I'm having trouble with the Speedo needle bouncing up and down.

My first thought was that maybe I put the wrong Speedo drive in when I rebuilt it so I ordered a new worm drive (red 12 tooth) and cable.

I took the old drive out and it looked ok: red 12 tooth and not obviously worn. But I replaced it anyway. I figured I might as well replace the cable as the grey plastic was peeling off in places, so maybe it had a kink somewhere.

I put the new drive in and new cable (they sent me a black one, which is a bit short, but it just about fits). The inner seems to be far enough in to engage the drive, and the inner spins at the top when spinning the wheel.

However, needle is still bouncing about, particularly at about 20mph.

Am I right in thinking the red 12 tooth is the right drive for a standard ETS?

If so, any thoughts what might be causing it?

Cheers,

[Yoshi]

Sounds like you have corrosion or dirt inside your tacho. Pain in the bottom to disassemble to get it cleaned but doable.

You have to pry open the edge of the chrome ring to get the glass off. Then it's just matter of handling the brittle plastics carefully and making sure to clean the innards real well.

Here you can see the parts of my -68 Primmy speedo disassembled:


Edit: just remembered that ETS has completely different style speedo.

[wilhets]

Yeh, it's a round one (10.5cm). Pretty much the same as a px one, I think.

The PCB is a bit dodgy on mine. So I guess it could be that, although it always has been like that.

I wanted to make sure I had three right drive and cable though first, before I start looking at the more expensive solutions. :oD

[jbcollier]

Cables are shipped dry. Try lubing the inner cable with light grease.

[wilhets]

Yep. Did that. Thanks for the suggestion though.

Does anyone know what the correct speedo drive is for an ETS?

[hrvespa]

Speedo drive worm should be 8 tooth for 10" wheels, the toothed nut inside the hub should be 10 tooth.