I didnt think the calibration would be significantly affected by friction. Meaning that the rotating magnet generates a current in the non magnetic disc that attached to the needle. That also generates a torque on the disk. That torque is resisted by the springs on the needle assembly.

The faster the magnets spin the greater the EMF in the disk, the greater the TQ, the higher the needed reads. Since calibration does not rely on friction, I'm not sure how lube would change the reading by a factor of four.

I have never seen an explanation of how a analog speedometer is supposed to work, but that's what it looks like to me. Did I miss something?

Kevin

I had a casual friend who worked at Speedometer Repair Service here in ATL, and the way he explained it to me makes sense to my rednek head. The only linkage between the cable spin and the needle movement is magnetic, as explained above. As the magnet spins past the ferrous pole of the needle linkage, the magnet pulls on the pole piece, and deflects it in the clockwise direction. The faster the cable spins, the more hits per unit time the pole piece sees, and the further it gets tugged clockwise against the needle spring tension. There must be some damping in the spring movement to avoid flutter in the needle, either from needle linkage inertia or mechanical friction.

I've found the best way to lube a cable is with a light grease on the cable and use a drill on low speed to feed the cable into the housing, and inspect the cable closely for any kinks in the housing, and minimize the tightness of any bends where possible. I once replaced an a/t cable with one from an m/t truck, and it was a little shorter, and the resulting tighter bend at the firewall turnup wore out the replacement quickly.

thats great info guys thanks. I will try some oil, if not my other speedo. if that isnt enough I give up haha.

wow!
Could you imagine just sitting on the porch in a rocker, in the sun, with a beer in hand and listening to Guns, Colt, Eddy, and Kevin sit a BS about life and cars??? <img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" />

The only reason I know about how the speedometer works is because I did design work on a damper mechanism for an inclinometer that's based on the same principal.

Totally random piece of knowledge.

Kevin

Quite a number of cable drive gauges have hydraulically dampened needles, generally tachometers. Of course I learned about these due to them not being stored in the proper position for a decade or two. Easy fix once they are opened up.
Oh I am sure professionals would say they are not rebuildable since they are crimped housings.

wow! that kicks <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> !

I am impressed as i can say the same also.





Even the newer elctronic instument clusters have fluid in the movements (jaguar , ford , etc). if you leave the cluster on its side it will cause a failure of the whole cluster! <img src="/forums/images/graemlins/frown.gif" alt="" />

I have heard that cars with these types of cluster are prone to fail if the owner parks the car a lot on a steep incline.




One of the most common problems i see with the japanese made speedometer sysytem is when the Speedometer will read 80 or 120 mph when the vehicle is traveling much slower.

the speedometer just goes to full scale right away as soon as you get going.

this is because tranny fluid has worked its way past the gear and seal and up the Cable & Housing into the back on the speedometer.

The fluid is forced into the lower frame and infects the rotating magnet. this oil now is the " friction " .

Since there is no longer air between the speed cup and magnet it grabs the cup and flings it up.


If rebuilt properly we would seperate the collar from the magnet shaft and clean everything up nice. then we would GREASE the bushing with light grease. We would only add ONE tiny little drop of clock oil to the speed cup where it rides in the magnet and put it back together and be done.

just one tiny drop of oil and a finger full of grease!

and that is why i am warning against putting " Too Much " oil in the speedometer. it would suck to have to pull it all apart later because you went crazy with the oil gun.

and believe me i have seen speedos where people did just that. <img src="/forums/images/graemlins/scared.gif" alt="" />

One thing I've found out about used cables (bikes and cars) is once its been run in one spot on one car ..You have to make sure the cable gets put back in the same spot and mounting as it was or the cable can stick in the cable housing and make the speedo do strange things ..

David

Hazardous Toys inc

I was pretty sure that's what he meant, to put it another way. the air gap between the non magnetic aluminum plate and the rotating magnet becomes a fluid coupling.

I just wanted to be sure that it was not something else.

Kevin