Ajs mod20 speedo gearbox 1958

[ralph ferguson]

Hi on rebuilding my bike I find that on installing the rear wheel the speedo gearbox locks up tight when the spindle nut is tightened. It then of course rotates with the wheel.all the parts appear to be there. Baffled!

[Mick D]

Hi

There's plenty of references to this issue on the forum and in the tech articles, here's one:

http://www.jampot.com/article_read.asp?id=82

If this doesn't answer your question a search most probably will

Regards Mick

[alanengineer]

Did you strip the wheel bearings

[JimFitz]

Be careful as the factory drawing is incorrect - cost me a new speedo cable. There is an excellent cutaway drawing in the tech help section.

Jim

[dave16mct]

This also a good guide. http://archives.jampot.dk/technical/Whe ... odruff.pdf
Dave

[ralph ferguson]

Thanks to all,I think that the hub innards had been done previously there is a useful article I think by a Mr Read but the cross section drawing at the bottom is obscured by the Clubs section on comments etc the other cross section drawing for some reason I cannot display much obliged
Ralph

[clive]

Ralph I assume the gearbox is not sized. Perhaps you do not have the speedo gearbox properly fitted so that "ears " fit in the slots in the adjusting ring for the wheel bearing. If you are sure they are engaged then I am afraid you cannot rely on "I think the hub innards had been done previously" as it sounds like the parts are not assembled correctly. It is a minefield with, as has been said, the factory drawing incorrect. There are two similar parts but they are used in a different way according to which side of the hub they are. As yours is locking up you are going to have to strip things out and check the order against the illustration on the website. Try viewing on a different size.

[JimFitz]

Thanks to all,I think that the hub innards had been done previously
Ralph

You can trust nobody but yourself on this - there have been several accounts of rear wheel lock-ups due to wrongly assembled hubs causing an off.

On mine the speedo cable fortunately snapped before it could get caught up but the speedo gearbox locked up and unwound the wheel bearing adjuster and jammed it against the swinging arm. I was fairly lucky as it happened off road and I had a sidecar on so it stayed shiny side up.

For your own peace of mind it is best to strip, check and rebuild. It may be that it was rebuilt by someone using the incorrect factory drawing.

Jim

[thornebt]

I had the same problem with my speedo gearbox. When I had a look at it the centre of the casing was dished inwards - must have been caused by me overtightening the spindle or the speedo gearbox retaining nut? The gearbox also ended up coming apart. Using an old appropriately sized sprocket a bashed it back into shape. I haven't fitted it yet as I glued the large ring (with felt surface) back in with some JB Weld glue to stop it falling apart again. I'm optimistic though as it does turn more easily now.

I know that the wheel bearings, spacers etc are correctly fitted as I had a nightmare doing them a few weeks ago! Cheers. Bruce.

[oldandsmelly]

I too had the same problem but it was due to fitting a new speedo gearbox when rebuilding the back hub after one of the aforementioned rear wheel lockups when the old speedo drive seized. Your post doesn't mention whether a new drive has been fitted.

The new speedo drives available are slightly dished outwards at the back face to the the hub compared to the originals. This dishing is only in the inner plate and not the outer body of the speedo drive. Some judicious straightening back of the outer plate with a small hammer solved the problem instantly and the new drive has worked well for a thousand miles ish so far.