Just got back from a blast before going to the gf's, and on my way back from Gainsborough I noticed my speedo slip backwards as I got towards 70mph +.

I'd reach about 70-80 and it would slip back then catch up with itself and slip again.

Anyone any ideas?

sound to me like the speedo cable is on the way out.
all the ones ive had go showed the signs your talking about until they stopped working completely.

Either that as above, or check the horrible nylon speedo drive on the sprocket, as they get old, they get brittle & get chewed up.

Had that, in my case it was the nylon cup. It fits over a tab on the drive mechanism, but the bottom of the recess for it had broken, so the tab was able to go all the way through. As a result, the cup was able to shift up the tab, and away from the gearbox sprocket nut, and eventually there was no purchase on it and it spotted driving the cable. In my case I was cheap and bunged a couple of washers between the cup an the drive mechanism to prevent it riding up the tab too far.

crappy nylon drive. mine broke 2 times and on the second the cable went too... but you know me, im used to it, i have learned to accept the problems my bike has.

Cheers for the replies.

Think I'll get the speedo apart later and check the nylon thing first

xivlia wrote:crappy nylon drive. mine broke 2 times and on the second the cable went too... but you know me, im used to it, i have learned to accept the problems my bike has.

You mean you have accepted the fact you havent fixed it properly.

After 20 years and expsosure to lots of heat it can be expected to be brittle from age. Breaking 2 means you didnt fit it properly or there is a problem with your speedo or cable.

If the first one lasted 20 years the second one should also last as long if everything else is ok.

To the op.

If it is the nylon drive sprocket make sure when you replace it that everything is clean and greased and the speedo cable isnt stiff, this will knacker a replacement quickly

Neosophist wrote:

xivlia wrote:crappy nylon drive. mine broke 2 times and on the second the cable went too... but you know me, im used to it, i have learned to accept the problems my bike has.

You mean you have accepted the fact you havent fixed it properly.

After 20 years and expsosure to lots of heat it can be expected to be brittle from age. Breaking 2 means you didnt fit it properly or there is a problem with your speedo or cable.

If the first one lasted 20 years the second one should also last as long if everything else is ok.

To the op.

If it is the nylon drive sprocket make sure when you replace it that everything is clean and greased and the speedo cable isnt stiff, this will knacker a replacement quickly

Cheers

So I finally decided to get off my arse today (on my first weekend off in 6 months) and have a look at this, especially seeing as my speedo stopped working last night and I had to play "guess what 30mph is" down a mile stretch of road with 4 speed cameras on it....

I took the drive system apart and everything looked fine. The widget was intact, the cable looked fine to me, so I de-greased it all, cleaned it and re-greased it and put it back together.



Then I turned the bike on, stuck it in first with it on the abba stand and the speedo worked perfectly all the way up to 20mph (was not revving the engine more than that with no load on it).

Now I'm off out to see if it's really sorted it.

So far the speedo is working fine, seems strange though how it could play up for no apparent reason...