speedo problem

[chrishewett]

My speedo has started to play up! It takes a while to reach speed and then when braking it stays at a high reading for a while and then gradually returns to a low reading. I think that when maintaining a steady speed it eventually reads accurately. I have this year replaced the rightangle drive which promptly failed. I then suspected the cable and so that was replaced along with a new drive ( at ?50 a time this is painful). All worked well for a while until this new problem. Any thoughts?
Chris

[niallf]

http://mywebpages.comcast.net/rhodes/speedo.pdf

This link may help.

Niall

[types26/36]

It takes a while to reach speed and then when braking it stays at a high reading for a while and then gradually returns to a low reading. I think that when maintaining a steady speed it eventually reads accurately.

Sounds like the speedo head is busy seizing up to me, try turning it with a a small srewdriver or the squared end off an an old speedo cable, it should turn with little resistance. If it is hard to turn then there is your problem.

[reb53]

I've only repaired a few speedos in my time but do repair clocks , barometers etc. for a living.
Bearing in mind how these speedos work I can't see how a cable or drive fault would make the needle sluggish to move and sluggish to slow down.
What would do this is one of two things:

the shaft the needle turns on is slightly bent making it reluctant to turn. (This seems unlikely as you would have needed to have dropped it !)

Something else is binding the needle such as old, or lacking lubrication.

This would have the effect of making the needle slow to follow the spinning drum and slow to drop when the drum slowed down.

Need to get it apart and have a look, probably find a spot of oil will fix it.

Ralph.

[Tonyw]

I agree with reb23 the mechanism inside the speedo or main shaft has probably gummed up or the lube has dried out, there is a magnet inside which "pulls" the main shaft to turn the speedo needle.

Tony W

[GrUmPyBoDgEr]

Reb53,
Tony W just demoted you by 30.
Is there some sort of feud going on down there in the Antipodes
John

[Tonyw]

Ooop's having a seniors day!!!!

Tony W

[GrUmPyBoDgEr]

Yup I know, they are a bugger aren't they

[reb53]

If anyone is having a seniors day I guess it is now me.

53 is my birth year...........

Ralph.

[JJDraper]

Re strange speedo behaviour - slow to speed up then, stays high when you slow down or even stop, before slowly coming down. This happened to my +2 a year or so back, and was more noticeable in cold weather. This points to a common fault with our speedos, but I'm afraid I ignored it, and after a while, it went away! 7k miles later, it hasn't come back..... I can't offer an explanation - perhaps a bit of condensation internally? Try running the heater on full pelt for a few miles.

For longer trips I tend to use a Sat Nav as the speedo, as even when its working the speedo is untrustworthy.... reads low at slow speeds and is wildly optimistic at high speeds. The sweet spot is around 60-65, when the Sat Nav and the speedo agree. A true 100mph is almost off the range of the speedo.

Jeremy