Speedometer Clutch Repair

I have intermittent faults with my speedometer, as I may have mentioned once or twice - either sticks at zero or runs around to full scale and stays there. This is caused by the clutch slipping and leaving the camshaft either with the commander pinion engaged, driving the needle right round, or failing to engage the pinion at all, leaving the needle at zero. As with many speedo failures, this is caused by over lubrication.

The first step is to pull the speedo out. Fed up with trying to maneuvre my hands under the top yoke, I removed the headlamp first:

This means that you can remove the cable, the speedo lamp and the little M6 nuts securing the speedo into the yoke very easily.

This post is not going to be a speedo rebuild tutorial. There is a lot of that already on this blog, and more in my forthcoming book. No, this post is just to record the rebuild of the speedo clutch; this first step is to strip the speedo down to the movement and then take the movement apart for cleaning and inspection.

This is the clutch, disassembled with the parts in the correct sequence. I have cleaned them with methylated spirit and a brush.

They are lying on a sheet of white paper - very useful for cleaning wheels!

Watchmaker...

So with the odometer and the speedo drive sorted out, it was onto the movement and the case. This is the movement as it emerged from the case:

The movement appeared intact on inspection, indeed it was just caked in grease and the debris from the mangled drive wheel. It was a simple matter to strip it down, then we sorted the various assemblies into separate pots for cleaning with pegwood, solvents & the ubiquitous toothbrush. Look at the colour of the solvent:

This took several rinses, followed by polishing of the wheels & arbors.  There wasn't any tooth damage to the wheels, and the various pivot holes in the plates are all in good condition.

Reassembled & lubricated the speedo now works nicely in the electric drill.The picture below shows it in position in the main frame, hooked up to the main drive & the odometer. We cleaned the odometer wheels (very gently) with a swab dipped in a mild water/detergent solution:

Next stop was the case, which required a trip to the shed to find the top yoke, since there was no strap for the speedo and no idea of what it should look like. A cardboard template and some of the inevitable sheet metal work soon remedied that problem, and the case was rubbed down and sprayed gloss black. The picture below shows the speedo in position in the top yoke, from underneath:

The dial and needle we left mostly as found - we don't want to polish all the patina away. I had the lamp holder still attached to the original wiring harness, so this was polished up using brass brushes in the Dremel, wired up and fitted back in place. some new M6 nuts finished the job - since the design of these instruments originated in France, all the fasteners are metric.

I love eBay...

After months of searching, I've found the correct S467/3/L speedometer for spares or repair on eBay! It looks good in the picture!

When it arrives, it's well wrapped in a box, inside 3 jiffy bags with newspaper around the outside. So, as soon as possible, we spin it up on the drill and...nothing happens. Well, the trip works and the odometer would probably have worked if I had bothered to wait...

If you've read the Bantam article, you'll know that I've repaired these before. When I got this one apart, we found the drive pinion spread around the interior like fairy dust. It shown in the pictures, minus all it's teeth.

As luck would have it, I had a Bantam 'D' speedo in the spares box, with it's drive spindle intact. This fitted straight in.

So next, I dismantled the trip/odometer drive (as you have to do, to get the drive spindle in or out) and cleaned up all the dust with a stick of jewellers pegwood, with a cloth swab taped to it. A dose of lighter fuel on the swab cleaned it up beautifully. Reassembled & lubed up it works perfectly.

Next job, number wheels. A similar swab but this time with a weak detergent mix cleans all the oil & grease off those as well.

Then we get on to the morass of goo that covers the movement. More later.