Yes, I know I said that there wouldn’t be an update for a while, but given that my odometer is not working and that it is almost certainly the delrin cog that has succumbed, I need a replacement. If I order it tomorrow, then it might be here for when I return from sailing. Anyway, as there are quite a few options, I first needed to remove said cog and count what teeth remained. Nothing to do with being soooo close to 20k views (you lot must have been bored over the years).
So, without further ado ….. the answer is 20x30, but if you want more, then fill yer boots and read on (or just look at the pictures) ….
Speedo was removed by the age-old method of removing the clock, and then pushing the speedo from behind. The clock is normally the easiest (well, less hard anyway) gauge to remove, but as they have not long been re-installed, mine came out most agreeably.
They look like this

I did make a note of how I thought that I had wired it, then checked prior to disconnection. It is quite simple, but only when you remember, so I made a note and stuck it to the steering wheel, just in case.
Then you remove the bezel – easier said than done. I tried a collection of different sized screw-drivers, knives and dental picks. In the end, tapping the bezel down onto the speedo and also across to one side helped. I hoped to get the bezel off from the bottom of the speedo, but the biggest gap was of course at the top, so that’s where I started. My smallest ‘normal’ screwdriver was the winner in the end. My watchmaker type screwdrivers were too flimsy and the knives just the wrong shape.
Once I had got a start, it was just a case of gently, gently teasing the bezel away from the speedo, inserting a blade under the bezel and encouraging it off.
Quick record shot of mileage before I played.
To remove the internals, first undo the 4 screws on the rear
Out comes the internals and the guilty party is revealed. The yellowed cog is well past it’s sell-by date, with teeth missing by the scroll drive gear (and more fell off as I handled it).
Removing the speedo needle was a case of brave pants on and turn (force ?) the needle past the minimum stop while pulling, then rotate past its maximum stop (while pulling) and repeat until the needle fell off. Quickly check to make sure that the needle had come off without breaking the drive needle from the instrument. Phew. Then 2 screws on the front face, and we’re getting closer.
That gives access to 4 more screws which are undone to remove the gearset
Noting where the metal plate lives
There are 3 sets of gears, with the first being removed by driving / drifting / pushing out the pin
The other 2 cogs are retained by tiny circlips, which I can surprisingly report, came off without breaking and without launching themselves across the room
Record shot of their orientation
Et voila, we have the offending cog removed
With my aged eyesight, I needed bright light and a magnifying glass to count the teeth. Having counted the remaining outer teeth 3 times and decided that there were originally 20, I noticed that they always only have 20. Hey ho. The inner teeth counted at 30, but I did notice on Design911’s website (other websites are available to check these things, but it was the first relevant hit in my Google search), a handy check – my adjacent cog has 40 teeth, so it would need a 20x30 cog, so good confirmation.
I told you that at the start, so thank you if you actually read the ramblings that followed. I've a little house painting tomorrow and then I'm off to sailing, so see you all in a jiffy.