calling all 36 speedometer doctors

[mrtexas]

How to fix this:

The speedo never returns to 0, rather 10mph.

I did an interstate hiway 10 mile marker test twice and both times the trip odometer read 10.3.

Tires are 650R16(28.36), stock is 600R16(29.26). This would make the speedo read low by 3%


Test vs GPS
30mph GPS speedo 38
60mph GPS speedo 67

 

[Lawson Cox]

Remove the speedometer from its housing. Look for a hole with a small Welch plug. Grind off the sharp end of a screw, making it flat on the end. Insert the screw carefully into the Welch plug and pull the plug our. With a needle or other similar tool remove the felt wick from the hole. Soak the wick in gasoline or other solvent and squeeze it out a couple of times. When wick is soft, put a couple of drops of oil on it and reinsert it in the hole from whence it came. (lol)

If possible, get a hypodermic syringe and suck a little 3 n 1 oil into it and gently oil any moving parts in the mechanism. Just enough to oil the part. Spin the speedometer with your fingers for a while and it should loosen things up a bit. You might take the end of a bad speedometer cable, cut it off and insert it into your variable speed drill motor (running backwards) and slowly turn the cable for a short while. then pick up the speed. Should clear up everything and lubricate the moving parts. The needle should settle back to Zero.

 

[rotorwrench]

A smaller circumference will make more revolutions per mile so it would be natural to increase the speed indication. There is a chart in the green bible about speedometer gear choices for different rear axle ratios and tire sizes but keep in mind the tires were bias ply and may have different circumference than the radial types when making comparisons to the old chart.

If the needle is hanging up in the speedo, the magnetic cup & needle shaft bearings may need some attention or the drag cup return spring is getting weak.

 

[ford3]

to add to what lawsons said, after removing welch plug and felt welt wick, put two or three drops of 3n1 oil in the hole where you removed the wick, then turn the shaft with your fingers, it might turn hard at firsr but keep at it till the shaft turns real easy, put a drop or two on top of wick when you have it back in the hole

 

[Hank the 36]

Thanks for the tips guys, my speedo is doing the exact same thing, 10mph when parked...