Had speedometer problems, did not work. I checked the speedo geat, the cable, the connections...all good. Took instrument cluster apart and pulled the speedo out. At first nothing turning it by hand or with a drill. Played with the external collar I guess you would call it to get needle to move. Hooked cable up and no work so I bumped the collar with my hand, speedo starts to work. The inside of the cabk of the speedo is clean, I shot a little wd40 in it for the heck of it. Put the cluster together, installed hooked everything up and took a drive, no speedo. Hit the top of the dash, speedo works. Park it for 5 minutes, jump back in, no speedo, hit dash, got speedo. parked it again and then took off, no speedo, kept driving and speedo started working.
It appears the needle is magnetic driven , is there a fix for this..or just plan on buying a new speedo to put in guage cluster?

 

I don't know much about this but maybe the needle gears or whatever is in there that spins it is gummed up? Other than that you might need to get a new one.

 

Oh the back of the speedo guage, from where the cable hooks in to the back of the speedo. The cable is turning what looks like a magnet, there is an outer collar or hub...this part moves the needle on the guage. As the magnet spins the outer hub starts to move,moving the needle to show speed. Hope that makes sense, wish I took pics, did not think about it at the time. The outer hub appears to be weighted so it returns to 0mph, then faster the magnet turns the hub starts to move and register speed. I did feel any resistance to the hub when moving by hand. Its like the outer hub gets stuck or the magnet is weak , once you bump it then the hub starts to spin. First time I have had a speedo apart so I dont know. Also found that the a/c duct hose were deteriated beyond repair and will need to be replaced. Other than that all the wiring looked good and unmolested.

 

It's been many years since I took apart an all-mechanical speedometer. But your description is right-on, you just missed the little torsion return spring. It sounds like a bearing is bad/sticky, if you have carefully looked to make sure that the cup isn't hitting something it shouldn't.

Wiki has an excellent explanation of how it works, read the part under the heading "Eddy Current".

Speedometer - Wikipedia, the free encyclopedia

I had an early 80's Ford that when it was real cold, zero F or so after being left out all night, the space between the cup and the magnet would close up enough that the magnet would intermittently rub on the cup. The speedo needle would suddenly kick way over, drop back, and kick over again, and making noise while it did it. As the car's interior warmed up, it would quit rubbing.

Trivia bit - If I remember right, speedometers in the US & Canada were based on a standard of 1000 revolutions per mile of the speedo cable. No matter how fast or slow you were going, the speedo head always saw that 1000 revs per mile. The faster you go, the faster the cable's core spins, therefore the 1000 revs occurs faster.
I assume the number 1000 was picked as it could be easily divided by 10, 100, 1000, etc. in decades by the Veeder-Root type counter wheels to create an odometer.

 

Well, i have no idea what any of that info is My speedo sticks a tiny bit at the beginning of my driving usually it kicks up around 15-20.

 

Thanks for the link, explains alot of what i saw.I did not see the cup hitting the magnet or anything else when I was messing with it. Did not notice the return spring either. On the plus side, my son said this afternoon it was working good today. Maybe it was just stuck from sitting for a long time. the guy I bought it from was telling me it was garage kept and out of inspection for 8 years when he bought it, then he had it for a couple yrs in his shop, then I bought it.