Eratic SX 200 speedo

[Rogthemod]

Can anyone help please with a problem I am having with the speedo on my Lambretta SX 200.  The old speedo packed up and so I bought a new one. 

It was fine when I first moved off but when I reached about 60mph the needle started to waiver and fall back.

I fitted a complete new speedo cable and ensured that both ends were firmly seated, adjusting the drive end a small amount.

Still no improvement and so I fitted a complete new drive.  Still no difference.

I have checked that the needle is secure, which it is.  I have put a small piece of inner in a drill and the needle reaches about 60mph smoothly and goes up and down depending on the speed of the drill.  I have attached the drill at the wheel end of the inner cable and carried out the same test.  Again perfect.

I am at a loss as to know what else to do.  It seems that the speedo drive is not staying engaged and I am wondering whether the internal moulding of the disc may have worn allowing the part of the drive driven by the cable to move?

Can anyone throw any light on this problem please?

[Lazy Dog]

Buy a new scooter

[heath]

So the speedo works but when you get to 60 its a gieder counter 

[Rogthemod]

Well I have read the article on restoring a Lambretta speedo in the December 2009 issue of Scootering and taken my old speedo which gave up the ghost apart.  It is one of the easiest tasks you could image.  I always thought the inside was complicated. I thoroughly cleaned and greased up the parts as recommended in the article and put it back together. 

I never like overhauling anything and not finding out what could have caused the problem in the first case. I noticed when I took the old speedo apart, the speedo casting was loose on the speedo assembly and on closer inspection I think this had allowed the end of the speedo worm drive to disengage from the speedo gear. When I reassemble to speedo I made sure firstly that the tab into which the top of the worm drive is held secure was adjusted slightly and the two tabs were well twisted to ensure the two parts are tight together.

I tried the speedo with a drill and hey presto I did 70 mph on the work bench.  Hopefully it will work when I put it in the headset and go for a road test.  If it does work, then the new speedo is faulty. If it doesn't     
 
 

[Rogthemod]

Yipee, my overhaul has been successful and I now have my "original" speedo working again, albeit that it is registering a bit faster than it was before it died.  (It always seemed to be on the fast side anyway)  I never thought I would work on a speedo!

[Lazy Dog]

Well done now get on with it you are starting to read like an American web site

[Rogthemod]

Well I have been able to establish exactly what is wrong with the new speedo and it is probably the cause of similar faults on others.  My friend who is a radar and electronics expert was curious to see inside the new speedo as he had been aware of my problems so I took it apart.

As soon as he saw the magnet inside he identified that as the problem. The magnet is not complete, the centre part being plastic.  Also, there is a chip in the magnet. He tested the magnet and said there was hardly any magnetism which would account for the fact that the plate attached to the needle shaft was not being held constant because of the lack of sufficient magnetism.  So there we are, nothing mechanical at all.  I shall be contacting the supplier who may not be aware of this specific issue

[Lazy Dog]

You must get a life

[Rogthemod]

I have got one - I don't work

[Lazy Dog]

You are a very lucky man