Here is another item from the "can't buy one so lets make one" files. I thought I'd share it here in case anyone else has come across the same problem.

A local fellow Amazon owner had problems with his speedo not working. The outer sheathing of the cable had deteriorated and the cable required re-building. The renewed cable didn't fix the problem. It turned out that the failed cable had locked up the speedo drive gear in the back of the overdrive - resulting in the plastic gear being chewed. New speedo drive gears are available for J type overdrives but the earlier 18 tooth drive gear for the D type overdrive (part number 380168) appears to be no longer available. The only options were to find a used speedo drive gear or make a new one.

I figured I should be able to machine a gear to suit. The old gear was pressed off. The part of the shaft where the gear sits is a straight knurled section so I figured that the original part was not cast in place but rather pressed on. I pressed on a suitable piece of plastic and machined it to the right diameter then used a little hand shaper attached to the lathe to carve the 18 slots to form the gear. The end result wasn't perfect but it certainly works OK. When viewed from either end the teeth appear to lean in opposite directions. This is apparently due to the straight line cut. The original gear profile is moulded in a helical path - the teeth have a slight twist from one end to the other. In practise the only point of contact is right in the centre of the teeth so the straight line cut on the new gear makes very little difference to how it works.

You can see from the photos how the gear was cut and the results. The divisions were indicated using a CAD generated 18 spoke wagonwheel printed onto a bit of cardboard mounted on the spindle of the lathe. I could manually line up a pointer on a line and then machine each slot down to the required depth. I am now inspired to produce a similar gear for my J type overdrive but with one extra tooth to correct the odometer.

I'd be interested to know if anyone else has had issues with D-type overdrive speedo gears, and if so how you went about fixing it. Maybe you upgraded to J type.

(I haven't figured out how to link multiple photos - see the next couple of photos in the gallery for more detail)