My 1959 speedmeter works still but has started acting funny.

I was somewhat inaccurate at higher speeds above 40 MPH, the higher you go the more it overstates your speed. So to go 65 it reads 75-80 I think.

At 40 and under it seems ok.

Now lately the drum is bouncing when I am moving slowly as in coming out of the garage. Once I get going the cylinder engages and works as above. Which is how it worked before, the car has no speed sentinel.

Again this model has the cylinder not a needle.

Is the drum failing or the spring on it weak?

 

These work same as a needle speedometer. Speedo cable rotates magnets inside the drum and induces a magnetic field in a cage inside the drum, causing it to rotate and do its magic act.

The bouncing tells me it needs a clean and lube and the inaccuracy tells me it may need to be remagnetized and calibrated. The one on my 69 Toronado behaved identically to yours and it also is a rolling drum type speedometer, less the color change feature.

You can try a clean and lube on the speedometer cable itself. Not sure if 59 drives it off the transmission or front wheel.

What size tire are you running? A smaller diameter tire than OE can throw accuracy off quite a bit.

 

You mean the cable needs a cleaning and a lube?

I am running the stock bias sized tires.9.0-14

 

The tires you have should not affect calibration.

Try the cable lube first and see if it helps. Disconnect lower end, pull it out of the casing 18" or so, clean old lube off with mineral spirits. Then put a light coat of medium bodied grease on the bottom foot of its length and work the cable back thru the casing till it seats in the speedometer head.

I don't think you'll have any problem getting it to go back thru the metal ell at the speedometer but by all means check and see what the service manual says about that.

If cable service doesn't help, time to review speedometer removal in the service manual and find someone capable of repairing it. Good winter job for when the car's put away for the season.