68 speedometer.

[68Zproject]

Were all the 68 speedos the same internally?  I just put my car back to idiot lights from an added console and tach.  What a rewiring nightmare, but everything works and it's back to the way it came out of the factory and I'm feeling a bit proud of all the work I've done to undo all the "restoration" some ignoramus did.  However, the old speedo was right on and this new one seems to read higher than the other one.  Nothing else was changed except the speedo.  Any ideas?

[bertfam]

There were two different speedometers used in 68. One with speed warning and one without. These old gauges were far from perfect, so the accuracy of one may be several MPH off from another. They can be adjusted, but you have to have special equipment to do it. It involves changing the magnatism properties in the magnet.

Ed

[68Zproject]

Nice.  There's a reliable service in Portland Or close to where I work called speedometer service.  I guess they do stuff like that and I gather that's what you're talking about Ed?  I probably should have had them test it before I put it in or would I have to know the amount it's off for them to adjust it?  I could change the gear on the speedo.  I just got flustered because my old one was spot on.

[JohnZ]

Nice.  There's a reliable service in Portland Or close to where I work called speedometer service.  I guess they do stuff like that and I gather that's what you're talking about Ed?  I probably should have had them test it before I put it in or would I have to know the amount it's off for them to adjust it?  I could change the gear on the speedo.  I just got flustered because my old one was spot on.

All GM speedometers are calibrated exactly the same way; 1000 rpm input from the cable will show 60mph on the speedo face; speedometer shops with the right equipment can calibrate them by adjusting the speed cup hairspring and/or re-gaussing the cup.

[bertfam]

re-gaussing the cup

That's it!! That's the term I was trying to think of when I wrote magnatizing.

Thanks John.

Ed

[68Zproject]

Thanks Ed and John!  When I get bored I can take it back out.