speedo gearbox problem

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Jul 19, 2003
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Just got the carbs set up on the bike and went out for a ride noticed that the speedo stopped working; not erratic movement, just stayed at zero. I found that the speedo gearbox has indexed by about 30 degrees clockwise and that grease that looks like it came from the speedo gearbox has spread out radially over the rear hub cover. See below.

Maybe the felt seal failed and as the grease emptied from the gearbox the gearbox seized. Before I take off the rear wheel and look into this, does anyone have some advice on what to look for? Any experience with a similar failure

Also, are there any recommendations for a source for a new or rebuild gearbox?



speedo gearbox problem
I would think the grease melted and ran out because the unit overheated?

Maybe the inner drive ring was being pushed hard up against the housing? Sometimes those drive boxes need a shim adding inside them.

You should be able to get a pattern replacement easily enough: http://www.nortonmotors.de/ANIL/Norton% ... 020&Part=5 and the genuine ones do turn up on eBay occasionally (Smiths type BG5330/171, 15:12).
I don't know of anyone (in the UK -at least?) who repairs them now, as I expect that would work out considerably more expensive than buying a new one?
Gearboxes are available new. check with your Norton Parts Dealers.

The drive engagement dogs may not have been engaged in the drive slots on the wheel. Sometimes the cover sticks out a wee bit too far and prevents the speedo drive from engaging all the way-then as the wheel axle nut is tightened it is misengagd allowing for it to spin. As you tighten the axle nut--rotate the drive by hand and you can feel if the dogs are engaged.
Other than this there really isn't too much else--you can if you wish install a grease seal on the drive unit in place of the felt seal and retainer.
And, by going to swap meets you can purchase old drive units and rebuild them by swapping parts around--ring gears and pinions are interchangeable as long as they are the same ratios.
This happens a lot---it's part of the pain-in-the-a@@ mistique of being a Norton enthusiast. After awhile you get to know more about the ideosycracies of your Norton than your Honey.
If you don't have the right spacers, shims and washers starting from the left side stub shaft all the way out to the right, bad things happen.
If the "top hat" spacer in the speedo drive becomes crushed, which they tend to do with repeated removal and replacement of the rear wheel, the speedo drive will contact the aluminum disc and try to turn with the wheel as evidenced in your picture. This spacer (P/N NM13270) should be examined routinely and replaced if the speedo drive contacts the aluminum wheel disc when test fitted by hand. Alternatively you can put a small spacer on the axle between the speedo drive and wheel spacer, but I find this very fiddly to install and the new top hat spacers are not terribly expensive.

In any case, with the axle tightened, make certain the speedo drive and aluminum wheel disc do not contact each other. If they do, shim or replace as mentioned above.

Your drive could be OK, but I would re-grease this as the heat generated by the friction of the aluminum disc grinding on the seal retainer appears to have generated enough heat to liquify it.

The other victim of this is usually the aluminum wheel disc. If it isn't too bad you can sand and polish out the scratches, but often a lot of metal has been removed.

I'd check that inner speedo cable also, from the kink in the picture, it could be worn or frayed.
The diagnosis that was suggested in the responses to this post is correct. The speedo gearbox was rubbing against the aluminum hub cover, to the point that there is a fairly deep depression in the cover and the material is almost worn away in the depression. That melted the grease which cause it to spread out radially from the source.

The gearbox still functions somewhat, but it's not smooth and it gives crunching sounds when I spin the inner race. So, I'll replace it with a new reproduction. The speedo cable looks pretty bad so I'll replace it also. I will replace the cover as well, this time being careful to ensure that the speedo gearbox is not rubbing. I also found that two of the cush drives are trash, mostly just a bunch of small pieces. Oddly, one of the cush drive sets is perfect and looks as new. I'll replace all them as long as I've got the wheel off.
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