VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 51 Chevy pickup speedometer

Speedometer reads properly when going slowly then drops to 10 mph when going above 25 mph. I unscrewed the speedometer cable at the transmission and attached a drill motor to the cable. The speedo runs smoothly up to 50 mph. Then I removed the speedo gear assembly out of the transmission. The plastic gear looks perfect and the input square looks fine both male and female. Could the problem be inside the transmission? The drive gear is at the top of the transmission and I don't have the repair manual to understand what runs this gear. Any help is appreciated.

The drive gear may be keyed or pressed on the output flange or perhaps the gear is clamped in place by the flange.

I'd almost bet the problem is with the speedometer. Have you had that out, cleaned, and lubed?

I agree with the above. Had the same experiance with my 1950. Removed the speedometer and had it professionally cleaned, lubricated and recalibrated.

When I test the speedometer in my 1952 3/4 ton pickup with a drill, the needle is slow to start moving and slow to return to zero (tends to hang up around the 20 mph mark). I’ve taken it completely apart and cleaned all pieces and then lubricated the gears and shaft pin with white lithium grease. Still slow to register and drop back to zero. Could this be caused by a weak spring or possibly the wrong lubrication?

I expect that the white lithium grease is way too thick to use in a needle movement like the speedometer.

I suggest one of 2 solutions. Take it out and try again but use a very small quantity of a very light oil. Or send it to a service to be professionally cleaned, lubed, and adjusted. Many of them use an ultrasonic cleaner so thing get very clean.

I agree with Rusty

I just had mine out and cleaned it out.
I dipped the very tip of an awl in 0W-20 and touched the two points where the needle shaft rotates.
Swung the needle back and forth a few times, then touched the area with a clean shop towel to wick away the excess.
Just got back from a good run and it works like a charm.

As to Krugerbenz's problem...
If the needle tended ot go too high, or even pin to the right, I would definitely say a good cleaning and lubricating may do the job. (I had to clean grease out from around the magnets on mine. I think it worked it's way in there from an over lubed cable.)
I'm not sure though what in the speedometer itself would actually drag the needle lower at higher speeds.
Seems counterintuitive.