Packard Forum Index » V-8 (1955-56)

My Panama with od reads high. Speedo says 50, I'm really going 40. Speedo says 40, it's really going 32. I tried to find the part number for the speedo gear in the parts catalog but could find no reference. I assume Packard offered various speedometer gears depending on the rear end.
Any thoughts?

For stick shift trans, gears are in group 3.257. 18, 19 & 20 tooth. The speedo seems quite a ways off. Wondering if the OD and rear end are stock or were changed and are you running radial or the original bias tires.

I swapped out the ultramatic for the od.
also swapped the rear end out of the donor. Yes, I do have radials. Good catch.

They run high....but yours seems over the top.

Speedo gears might be available from Roscoe Stelford in Hampshire, Il.....

I think with all the switching you have done, they all play a role in the inaccurate speedo.

I was careful about the switch. The transmission, clutch, rear end all came from the same donor car. Only question is the radial tires. They are much larger than standard.
I was thinking of compensating for this with a different speed gear. Does this gear come out of the housing the same as on the ultramatic?

Quote:

Unless I'm missing something won't a larger diameter tire make the speedo read lower than actual. Usually the complaint on the average radial is the diameter is smaller than bias.

Yes, I agree with you. A larger diameter tire should make the reading be lower. I will compare the diameter to the bias ply I have here.

Quote:
Similarly, but with different types of parts (P/Ns) between standard (Grs. 3.256-3.257) and Ultramatic (Grs. 3.681-3.686).

Unlike later GM vehicles that I've worked with in this regard on, the spread on speedo pinion (driven) gears listed for standard and OD in the Packard V8s is only a bit more than 10% (depending on which way you look at it), and there's only one choice of driving gear for overdrive (another for standard trans).

You should first determine the ratio of the current rear axle to see if you have the right tooth count on the existing speedo pinion gear. Without knowing the full history of the donor car, it could very well be that some other axle ratio had been installed that isn't regular production - not supported by any available speedo gears.

You might want to consider an inline speedometer ratio adapter. Though not exactly cheap, they may be easier to find and provide a more accurate reading than any available gears for the transmission.

Mind you, that's all assuming that your speedo head was accurate, to begin with.