my 1966 300 with 440 , speddo is 17 mph off, what color pinion do i need

[greg yoder]

been thru this on my 71 imperial, yrs ago, it was 10mph off, on the speedo, had to change the pinion on the end of speedo cable, they have all kind differant colors, i have 14 in tires, at 70 mph on the speedo, im running 53 mph, clocked on my gps, any input on what color i need to change to??

thanks
Greg Yoder Lafayette ind

 

[FURYGT]

A factory parts book will list the Speedo pinion gear in a chart with tire size and gear ratio. Determine the diameter of your tires and determine which tire size listed in the chart has the closest tire diameter to your tires and that will get you the part number for the speedometer pinion gear that’s going to get your speedometer reading as close as you can get it.

 

[Big_John]

been thru this on my 71 imperial, yrs ago, it was 10mph off, on the speedo, had to change the pinion on the end of speedo cable, they have all kind differant colors, i have 14 in tires, at 70 mph on the speedo, im running 53 mph, clocked on my gps, any input on what color i need to change to??

thanks
Greg Yoder Lafayette ind

 

[Blusmbl]

I knew my tire size and axle ratio, ended up swapping from 4.30's to a 4.10 dana in my '68. I bought the appropriate gear based on the Brewers chart, and when I put the new one in it was still off. Looking at what came out of the trans compared to what should've been in there, I then applied the ratio difference to the new gear I picked up and then ended up with the correct speedometer reading. I don't know if the error is in the speedometer itself or if my output shaft was wrong, but it wasn't right for an early tooth count either so I have no idea why it is off by a few teeth.

I'd definitely pull your old gear out first to see if it's correct for the tire size and axle ratio, and then work from there.

 

[CBODY67]

On my '67 Newport w/P245/70x14 tires and 3.23 rear axle . . . when the speedo reads 70mph, it is only 63mph road speed. BUT, the odometer is dead accurate at that speed, which means the CORRECT gears are in the transmission!

The odometer is geared to the speedo cable, directly. The rear speed cup on the speedo head is also directly connected to the speedo cable, too. The rear speed cup has a bar magnet in it, which rotates the front speed cup (to which the speedo needle is attached). The front speed cup works against the clock spring that returns the needle to zero each time.

In speedo shop calibration of a speedometer "to speed", they use what I term a "zapper gun" to vary the magnetism level of the bar magnet, to get a lower or higher speed reading on their test machine. A purely cut and try method to get the best speed readings over several calibration speeds.

Now, what you describe is a common request to correct the speed readings. Easier than taking the speedo head out of the instrument panel. ONLY thing is that when you change the gears in the transmission, you then affect the odometer readings. Which can THEN change any fuel economy checks you do after that! IF that might matter to you or a futur4e owner.

FWIW,
CBODY^&

 

[66 Monaco 500 365]

If the spedo is off by say 5 MPH at 20 and 5 MPH at 70, the needle has moved on the shaft, you will need to disassemble the spedo and move the needle to compensate.
If it is off by 5 MPH at 20 and off by 10 at 40 and 15 at 60, that is corrected by a spedo gear change, it is a proportion.
If it is off by 5mph at 50, it is 10% off.
Increase the tooth count by 10% to make the reading 10% slower: go from 30 to 33 teeth.
If you need to make the speedometer 10% faster, you would reduce the tooth count 10%, go from 30 to 27 teeth.
My $.02