Smiths Speedo drive overhaul

The speedo drive is a fairly simple assembly, just consisting of a worm gear and pinion. However, they can be awkward to get apart.


The pinion is retained in the body by a small pressed steel plate, which is retained by 4 screws. You will see these if you look inside the housing. These can be a sod to remove, my only recommendation would be to heat the body in warm water before attempting removal. If they are tight there is a possibility one or more will shear off. That is repairable though. The holes can be drilled out, tapped slightly oversize and larger than original screws used.


Also pressed into the body and covering the pinion is a metal cased rubber seal. This is just pressed in and can be carefully prized out using a small screwdriver. Again this is best done with the body warmed to ease removal. 100 degrees C is ample.


When the seal, four screws and the retaining plate have been removed the pinion is ready to be removed from the body.


Next undo the brass fitting that retains the worm gear and shaft. This has a right hand thread, take care not to damage the body when undoing this. The material of the body is 'punched' into one or more of the slots in the brass piece as a method of locking it. Generally it can still be undone despite this. I normally hold the brass fitting in a vice between two sheet metal jaws and turn the body by hand to get it started. A dab of Loctite will hold it OK on reassembly.


Once the brass piece has been removed the worm and shaft (which are one piece) can be withdrawn. The worm shaft has small, separate spacer(s) fitted over it, take care not to lose it (them) and note their location. After the worm has been withdrawn remove the pinion to complete the disassembly.


When refitting the unit to the bike note that there is a spacer fitted over the wheel spindle against the bearing locknut and inside the drive unit to support the casting when the outside locknut is tightened.