Speedometer Gears

[grayhitandmiss]

Went for my first ride in my 64 yesterday after six years of looking at parts. So far so good, but as I was expecting, my speedometer is "off".
According to my GPS, at 55 mph, my speedometer is reading 48 mph, at 30 mph, it's reading 25 mph.
I don't know my rear end ratio. I have a SM420
4 speed tranny. Without getting too scientific, could I just purchase the next size speedometer gear, and get "lucky"? I find four different gears available,
with 18, 20, 22, & 24 teeth.

If my speedometer is slow, would I get a driven gear with "less" teeth?
My gear has 19 teeth, so is "less" is the way to go, it looks like I only have
one option, with the 18 tooth gear.

My original gear is metal, and I can't see how it's attached in it's
housing. Is there a clip deep down in the bore, on the cable end?

Thanks for any help!
Tom

 

[grayhitandmiss]

Speedometer gear removal

Attached is the photo of my speedometer gear in the housing.
How do I remove the gear from the housing so I can
replace the gear? If there's a clip inside the bore,
I can't see it, and it would be too small to get any
tool in there.
Thanks for any clues.

 

[dcsi5919]

Hey Tom. I have a number of those and I don't think the gear removes from the shaft portion of the assembly. It appears they are fabricated/constructed, the way you see it in the photo.

 

[grayhitandmiss]

One of the parts places has four option of different teeth gears, in which they say fits the four speed trannys, as well as the 3 spd, etc.
They're showing plastic gears with a shaft, for about $7
No housing shown or mentioned.
Is their data in error?
At any rate, I'd have to find a gear to fit with 18 teeth.