[XLR8STEVE]

OK you gurus, here's a good one.
My speedometer went haywire and i took it apart.
I got the spinning mechanism to turn smoothly.
When I put it together and use a drill to simulate the cable spin, it doesn't seem to behave properly.

-The cup to housing coil spring is intact
-The driven portion spins freely inside the cup
-if i assemble with one full turn on the coil spring it seems to be too much and spinning the cable mount doesnt move the needle.
-if i assmble the cup with no turns on the coil spring it moves but it won't return to zero
-if i put slight pressure on the needle mount towards the back it seems to behave the way it should

Are there any parts missing between the cup and the driven portion of the speedo? I have some very small rod that was loose in there 1/4" long and 1/32 diameter. That was all that was inside.

Any help is appreciated. Seeing if i can do this myself before sending to a speedo guy. Doesn't seem too complicated.

[Peter Serio]

Once you remove the speed cup from one of those old speedometers the magnetic field collapses to less that 1/2 strength. There is a delicate balance in the relationship of moving parts that support the speed pointer. It takes years of experience & several special tools to reassemble one of those so that it works properly.

Since you have taken yours apart without a DC magnetizer and an AC De-magnetizer (to calibrate) you will never get your speedometer to read accurately.

Whenever working on these you need a way to spin it to test it. The final check-out goes by RPM.
On all older model rear wheel drive GM cars using a cable driven speedometer (except 1965-1969 Chevrolet Corvair) the ratios are:
500 RPM= 30 MPH, 1,000 RPM= 60 MPH and 1,500 RPM= 90 MPH.

I work on these every day around here, PM me if you have any questions.

[XLR8STEVE]

Thank you Peter.