1957 Adjust speedometer needle

[57DukeofAle]

When my car is stopped the speedometer needle is 10 mph below zero. Therefore all my indications are 10 mph low. Is there an adjustment for the needle? I have not found any information on this.

Dukie

 

[Ward 57]

The bezel and lens are held on with spring clips. You can pop it off and maneuver the needle like adjusting clock hands. spin it up until you hit the stop and if the needle isn't frozen to the post you can just move it further for the approx 10 MPH.

 

[dmsfrr]

Yes the needle is adjustable but I've not had one apart. I probably don't have the tools or knowledge of 'how' to properly do the work.
It may be as simple as a missing lower stop-tab for the needle to rest against, or the needle being slightly loose on the shaft.

Otherwise I take mine to a local speedometer shop for cleaning and adjustment.

You can easily do something to help check out another part of the other function.
Check the odometer for correct distance against GPS or 5 to 10 miles worth of mile markers on the hiway.
The odometer is gear driven and usually more accurate, if the driven gear on the lower end of the speedo cable is 'correct', along with matching gearing in the differential.
The speedometer moves based on springs & magnets and is more likely to be affected by dust buildup, lack of lubrication or something being out of adjustment.
If the odometer distances match what the GPS or mile markers indicate... the gearing is correct and the (65+ yr old ) speedometer mechanism itself needs internal attention.
If the odometer doesn't closely match a known distance, that correction would come first before trying to get a correct speedometer reading.

Example... the odometer in my '55 is 99.9% correct when checked against known distances, but the speedometer reads approx 15mph high.
So I know the gearing and input to the speedometer head is correct and the problem is something mechanical in the speedometer or its calibration & adjustment.

 

[doug7740]

Thunderbird odometers are calibrated at 1,000 revolutions of the speedometer cable per mile on the odometer. The rate of turn is controlled by the tooth count on a plastic gear at the transmission end of the speedometer cable. In your 1955 speedometer example, since the odometer is 99.9% correct when checked against known distances, the speedometer cable is turning at 1,000 revolutions per mile and the gearing is correct. Since the speedometer is reading 15 miles per hour high, the speedometer will have to be removed so it can be calibrated. On a 1957 Thunderbird the speedometer can be removed from the back of the instrument cluster, but on 1955 and 1956 Thunderbirds the instrument cluster will have to be removed.

The speedometer head should be calibrated to 60 miles per hour at 1,000 revolutions per minute. I use a reversible electric drill with a top speed of 1,000 rpm as my test fixture. To calibrate your speedometer, adjust the return spring on the speedometer needle. Look closely and you will observe that the return spring is pinned to the housing at the outer end. Using a small screwdriver you can gently rotate the pin location to increase or decrease the tension on the spring. Make small adjustments until you zero in on 60 miles per hour.

After the speedometer is back in the car you will see the results of your efforts.

doug7740
1955 Thunderbird Blue

 

[dmsfrr]

Thunderbird odometers are calibrated at 1,000 revolutions of the speedometer cable per mile on the odometer. The rate of turn is controlled by the tooth count on a plastic gear at the transmission end of the speedometer cable. In your 1955 speedometer example, since the odometer is 99.9% correct when checked against known distances, the speedometer cable is turning at 1,000 revolutions per mile and the gearing is correct. Since the speedometer is reading 15 miles per hour high, the speedometer will have to be removed so it can be calibrated. On a 1957 Thunderbird the speedometer can be removed from the back of the instrument cluster, but on 1955 and 1956 Thunderbirds the instrument cluster will have to be removed.

The speedometer head should be calibrated to 60 miles per hour at 1,000 revolutions per minute. I use a reversible electric drill with a top speed of 1,000 rpm as my test fixture. To calibrate your speedometer, adjust the return spring on the speedometer needle. Look closely and you will observe that the return spring is pinned to the housing at the outer end. Using a small screwdriver you can gently rotate the pin location to increase or decrease the tension on the spring. Make small adjustments until you zero in on 60 miles per hour.

After the speedometer is back in the car you will see the results of your efforts.

doug7740
1955 Thunderbird Blue

@doug7740,
Thanks for the excellent information and photos, they'll be very handy when I tackle this project.
Hopefully they'll help 57DukeofAle just as much.

.

 

[biddle]

doug7740,
Thanks for the excellent information and photos, they'll be very handy when I tackle this project.
Hopefully they'll help 57DukeofAle just as much.

.

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