[1project2many]

There are many, many things I'll do myself but I had no hesitation about sending the speedometer out. The speedo works with magnets on a disc that spin inside a drum. As the magnets are spun by the speedo cable they "pull" the drum causing it to turn. A very small clockspring attached to the drum resists the effects of the magnets. It's a balancing act and when calibrated properly the speedometer needle will register 60mph when the disc spins 1,000 times per minute. The calibration is so sensitive that you can have problems with changes in temperature as the viscosity of your lubricant changes. Additionally, replacements for damaged clocksprings, worn bushings, and bent shafts can be very difficult to locate outside the speedometer repair industry.

With that said, erratic needle operation on an old speedo is often caused by dry or "sticky" grease. Cleaning it out with a good cleaner is the first step to curing the problem. Once the old grease and accumulated dirt is removed the next step is to get the parts properly lubricated. I have a tube of "Darmex grease" which was once available through GM that is about the best lube I've found for speedometer heads and cables. It was actually called out by part number in some old service manuals and was the recommended lube for automatic front hubs used in the early to mid-80s. Ford specs a Darmex grease for their auto hubs as well... unsure if it's the same product though.

After the speedo is lubed you'll need to check calibration. 1000 rpm of the cable should be 60mph. You'll need to come up with a way to drive the speedo at 1000 rpm though. Calibration can be as simple as turning a screw or as tricky as loosening a pinch clamp and stretching the clockspring slightly. Of course you should check at several cable speeds in case the spring rate is not correct. It would suck to get a ticket because your speedo is off at 30 mph.