Rear wheel speedometer gearbox

[mjf65]

I thought that things were going too well. After fixing the dynamo oil leak and having a working speedometer on last week's shortish test ride.
I was heading up to Cirencester tonight via a little circuit but I only got as far as Avenging when the bike felt unusual and the Speedo stopped working. A little further down the road the rear alloy wheel cover started rattling as it was loose.

After roadside inspection there was speedometer gearbox grease all over the rear wheel rim and the gearbox has been forced into the spindle spacer so you can hardly see the nut which attaches it. The cable had broken and was detached. I managed to limp home but I can't get the speedometer gearbox off, it's solid. I don't want to start thumping things with big hammers.

This is annoying as it happened to me before due to a worn speedometer gearbox sticking and unlocking the bearing adjustment ring causing the wheel to move outwards. I can't understand why it would happen with a good smooth speedometer gearbox? Am I unlucky?

[clive]

Possibly unlucky possibly the spacers are in the wrong order. I am on the move today but there is an excellent cut away drawing hub showing the correct order (some manuals are wrong). Someone will put up a link to the picture. (Spriddler? )

[SPRIDDLER]

Someone will put up a link to the picture. (Spriddler? )

This is the best photo by Biscuit.
In the link to 'Photos' in the Technical articles section (Here: https://www.jampot.com/pic_display.asp?id=820 ) it's shown with the individual parts numbered and described but the numbers don't show up very well :

Rear hub by Biscuit.jpg

Rear wheel assy parts list.JPG

I've edited the original photo to show the numbering more clearly, (hopefully I've got it right)........

Rear hub assy numbered more clearly.jpg

[clive]

Well done Spriddler. Michael do check all the parts in your hub to check they are in the correct order. Some are not what you would logically expect, especially the oil seal. On the left hand side this sits in the oil seal holder. On the right hand side it does not, it abuts up against the holder and is retained in place by the ring small no 9.

[mjf65]

Gents, thank you so much for your help, I'd seen the photo before but clear relabelling is much better.

Unfortunately this isn't the first time this has happened to me so I know I have all the right bits fitted in the right order as I had to replace the oil seal as it was damaged last time. The first time I traced the problem down to a worn speedometer gearbox which locked up which then causes the bearing adjuster ring to unwind causing an axial load outwards. I was lucky that time as it happened at the end of my road. Anyway, I knew that was the problem and I repaired it and also removed the worn crown ring from the gearbox so there was no chance of it happening again and that has been the case for the last three years, i just use a digital bicycle speedometer. However I obtained a good genuine Smiths gearbox with no detectable play and fitted that last week, I'd been advised to steer away from poor quality imitations.

I'd done about a thirty mile run last week after fitting the new gearbox with no problems so I was out yesterday evening when the same thing has happened again but I've had to use a lost of force to remove the gearbox so a number of new parts are now required. To me it seems a poor design feature using the bearing adjusting ring to drive the crown wheel, I would have though the crown wheel would have been brass so it would fail safe rather than steel on steel?

I know I'm not the first person this has happened to as others in the Bristol section have experienced it. I suppose the answer is check for freedom of movement regularly and lubricate the speedo gearbox at the same time or just ditch it completely which I'm going back to.

[les ward]

The only time this happened to me was after a puncture. So I make sure the first thing I undo is the nut that holds the speedo gearbox and make sure this is the last thing to tighten. My theory is that if this isn"t done and the spindle nut is tightened more than before, then there is too much pressure on the bearing adjuster.