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Speedometer Problem

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Hi,

The needle in my speedo has wobbled around since I purchased the car many years ago and so recently I took the decision to replace the cable from the gearbox.

The old part had plenty of oil around the inner cable.

The new cable appeared to be sealed and so no attempt was made to inject oil between the outer sleeve and the inner cable.

I ran the car for some 15 miles and the needle gave a steady speed. Then the speedo started wobbling again and the speedometer ran with a distressed noise.

Should I attempt to inject oil into the back of the speedometer or is there another solution please?

David

 

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My McAfee says that is a dodgy download. Please virus check.

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No problem with that one  :-)

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These cables were traditionally greased not oiled. 

Any kind of oil/grease getting into a speedo head will mess it up.

They work by a spinning magnet dragging an aluminium disk against a light spring.  This works because of induced eddy current in the disc.

The magnet does not spin very fast and this mechanism does not generate much torque.  Just about enough to move a needle.

 

 

 

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Non-steady speedo needles seems to be a common problem. One speedo I looked at recently had wear on the bearing (bush) on the input drive. This was enough to cause the needle mechanism to contact the spinning magnet mechanism inside. The needle would reach 120mph and then drop back and so on.

I have posted this answer before elsewhere on the forum but it seems to be important to make sure the cable is routed without any significant bends and goes through the correct grommet hole in the bulkhead (the one behind the speedo) and lines up as near perfect as you can get it with the input at the back. Then the knurled locknut only needs to be finger tight. One symptom of not getting this right is that the needle doesn't zero properly. I quick fiddle around with the knurled locknut at the back or a slight movement of the cable and the needle drops to zero.

Do not put oil or grease  into the back of the speedo - it will cause problems inside. Everyone has their preferences but I find some light 3 in 1 oil on a paper towel and just wipe it down the cable inner is enough to lubricate it. Grease in my experience will cause drag on the inner cable and could cause the needle to waver. Friction from grease is higher than oil. Also do not 'inject' oil into the cable - it will be too much and could end up inside the speedo. Just a light smear from a paper towel is more than sufficient to prevent sticking.

I think one of the problems is that many speedos are now over 50 years old and the cars have often been once or even twice around the clock. They were never really designed to last that long. Wear on the input bush seems to be a problem point since the spinning magnet will have done millions of revolutions in its lifetime. The moving part that the needle is attached to doesn't have that much movement so is generally ok. The only problem there seems to be  a weak spring or loss of magnetism. 

Keith

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Thanks Alan and Keith,

I have attempted to reinstall the cable into the back of the unit. Again all ran well, quietly , and with the correct speed for say 5 miles.

Then as before the wobble commenced and a noise came from the speedo.

I also noticed that the indicated speed was too low.

Regards

David

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Hi Keith,

I believe that you solved the problem. Today I offered up the cable to the back of the speedo and gently pushed in the cable end.

So far all seems to be working accurately and without noise with the knurled locknut not attached.

Thanks

David

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Hello David

I'll keep my fingers crossed then. The knurled locknut should be attached to stop the cable falling out of the back of the speedo even if it is only a few turns (loose finger tight). Very temperamental these speedos seem to be. Mine runs fine for ages then I do something with the wiring, move the cable a fraction then have to find the 'sweet spot' for the cable again for everything to work properly. I don't remember this happening back in the 1960's on the Herald or Vitesse my dad had.

Good luck

Keith

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Hi David,

 if/when the noise starts again put your hand under the dash and push the cable around. You may well find a position that it doesn't squeak in.

Using plastic ties lock it in this position.

 

Roger

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