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MG MGB Technical - speedometer trouble

I have a speedometer that gets worse the faster you go. Up to 55-60 it is fairly steady and accurate, but does show some slight dancing. Once you get up to 60-65 it jumps about 10-15mph then enventually smoothes back down, but never completely steady. Above 60 is will dance between about 4-5 mph back and forth. I have checked the cable, it is new and does not seem to be in a bind. Has anyone had a similiar problem, is there a home remedy? Thanks for any help in advance.

Brian

How often does the needle dance? In time with movement of the odometer? Or several times faster than that? If faster it almost certainly is the cable, and I can imagine certain speeds where 'harmonics' will cancel things out and make it smooth. If it is in time with the odometer movement, or gets noticeably worse with it, then it is probably stiffness in the speedo itself, possibly combined with a stick cable. Some say don't grease the cable it it works its way into the speedo head and wrecks it. But I cured stiffness in the speedo with a drop of light oil on the input shaft and many thousands of miles later it hasn't caused any collateral damage.
Paul Hunt 2

Yes the odometer does also move somewhat sporadic. It will goe slow, then jump. It is worse with fast acceleration. The needle will jump back and forth about 5mph above and then below the speed I am actually at. Then for ex. if hold steady at 65mph, alfter about 20 seconds it will steady out and dance between 63 - 67mph, split the difference I am at 65. I dont know why I did not put two and two together, with the odometer binding some it probably is speedo stiffness. This was a used speedo that has sat a while. On the back at the input shaft you just put a drop or two on the outer edges of the input shaft?
Brian

A tiny drop of oil from a needle oiler used for model railroad enginees on the bearing surfaces and shafts did a good job of steading the speedo in our A.
John H

I guess in order to oil the bearings I need to remove the face? Will that give me access?
Brian

I mean't does the needle jump with each movement of the odometer, but no matter.

In my case a drop of oil on the input shaft did the trick i.e. remove the cable from the speedo and the speedo from the dash, and put a drop of oil on the end of the little shaft that has the square hole for the cable inner. This is in the middle of the threaded part that takes the outer.
Paul Hunt 2

Thanks for all your input. I pulled the speedo out and oiled it, then put the cable in my drill to spin it. No fix. It seems this speedo is shot. I had an old speedo up on a shelf though, so I checked it and it worked. The downside is it didn't look that good. I pulled the needle and face off of the other and put on this one. Now I have a good looking, WORKING, speedometer. •tip for anyone taking a needle off, spin the speedometer in a drill, or anything you can do accurately over and over. My drill spins 60mph wide open. I kept adjusting the needle until it read 60 with the drill going all out. Again, Thanks for all the input!
brian

I recalibrated mine when the needle popped off by calculating the revs for a 30mph in a given gear, jacked up one rear wheel, set the throttle for the calculated revs, and pushed the needle onto the spindle with it pointing at 30mph.
Paul Hunt 2

This thread was discussed between 14/08/2007 and 17/08/2007

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