Speedometer pinion gears, help needed!

[OneEyed]

Speedo hasn't been correct since I've owned the car. It reads about 20 mph too fast. Finally got around to pulling the pinion gear and its the Red one. The service manual states that I need a white one. So I ordered one off ebay. But the difference between the red and white is ONE tooth. Would that make all the difference?

My tires are 215/75-14 which should equal a 8.25-14.

Also, what do you guys know about the adapter and needing to be in the correct 6-o-clock position? I didn't notice how it was when I pulled it, but made sure to get it correct when I re-installed the red gear. Now the speedo doesn't work at all. Not really wanting to pull it again til the white one shows up though.

The gear that's up inside there, does that move when you shift to make contact with the pinion gear? Or is my 6-o-clock position wrong? There is a nipple on the edge of the housing that points straight down to the ground, so I used that as my reference point. But the service manual pic looks a bit off, they show the bolt hole for the retainer to be at about 8-o-clock when in reality its like at the 11-o-clock on my car. Maybe its a stock photo of a different tranny? or maybe I need to rotate it?

'67 Newport base. 383 2 barrel, 727

 

[Bart]

In addition to the color white, there will be a specific number stamped into the gear. On the speedometer gear assembly that attaches to the transmission, there are two or three series of numbers. It will say something like "19-32" on one series, and "33-40" on the next series, etc. (Do not quote me on the numbers, just that there are several series of numbers). The number stamped on the gear will fall within the range of one of those series. Put that series at the 6 O' Clock position, and you are good to go.

I should warn you, however, that gears of the same color may have a different tooth count. That is why you need tooth count AND color to determine which gear you need for your gear ratio and tire size... hopefully, you chose correctly!

 

[1966newport]

is odometer also may off?

 

[OneEyed]

Not sure if the odometer is way off. I guess I can check by watching the trip odometer. I had the white 27 gear put in but it is still of by about 5-10 mph now, which is better. What else can I check?

 

[Big_John]

If the speedo is off, the odometer is off too.

Here's a chart of correct speedo gears for axle ratio and tire diameter.

Mopar Speedometer Gear Selection Guide - MyMopar.com

 

[Big_John]

I should have added, you can't really cross metric tire sizes over to the old sizes. Instead, you want use tire diameter as your starting point. You may also want to double check your axle ratio.

 

[Bart]

Yes, Your ratio is only correct for the original sized tire. If the gears came out of a different vehicle, you will need to determine the ORIGINAL tire size, and find the correct speedometer gear accordingly. Taller tires equal higher effective gear ratio...

 

[1966newport]

if the speedo head calibration is messed up the odometer will still be correct

 

[Bart]

Gear Ratio Calculator


This may help you.

 

[OneEyed]

So, if I'm correct, my tire size puts me at a diameter of 26.7 inches. Do I then assume a 26" for that chart? I'm not certain of my gear ratio, but I do know it was 2.(something). Assuming that, that would put me in the white or yellow gear category...
SO, maybe I need the yellow one now instead?? I'll have to try and get underneath there again and read the ratio tag i guess.

 

[Big_John]

First, I'd actually measure the tire diameter and not assume that the chart is correct for your tire. Then, yes, you need to know your gear ratio. Without those two pieces of information, you're just spinning your wheels.

 

[OneEyed]

There's a tag bolted to the transmission that says 2.76 and my best attempt to measure the tires comes out to be 26.5" diameter.

That info still leads me to the white 27 tooth gear.

Thinking out loud now, the red 26 gear had me about 20mph fast and the white 27 put me about 10mph fast, so it looks like a yellow 28 should get me closer?? Any ideas on that?

Plus, since there was a red gear in it when I bought it, can I assume that transmission had been swapped at one time? or maybe the wheels were downsized? I bought the car thinking (was told by previous owner) that everything was stock/original. But then again, he was wrong/hid the truth about other things as well.

 

[Big_John]

I looked at the chart I linked and I come up with a 28 tooth gear.

If you are still fast with the 27, the 28 will slow the speedo down and probably will be correct. The speedometers are always running a little faster than the actual speed (like shown on a GPS).

 

[Bart]

One tooth is good for 3-4 MPH.

 

[1966newport]

the speedo heAD IS SCREWED UP

 

[OneEyed]

I looked at the chart I linked and I come up with a 28 tooth gear.

If you are still fast with the 27, the 28 will slow the speedo down and probably will be correct. The speedometers are always running a little faster than the actual speed (like shown on a GPS).

I guess there's a difference in info. A 28 tooth gear with that part number brings up a blue gear on ebay. Where as my white one says 27 on it. Heck, my service manual only lists a red or white gear for a Newport and shows a yellow 28 for the Imperial.

But either way, it looks like I need a blue 28.

 

[Big_John]

I have no idea about what the correct color is. I only go by the tooth count.

 

[OneEyed]

Got around to purchasing the blue 28 tooth gear and installing it the other night and the speedo is still off by about 10 mph. Not sure what to look at now....

 

[Big_John]

Got around to purchasing the blue 28 tooth gear and installing it the other night and the speedo is still off by about 10 mph. Not sure what to look at now....

You ought to double check the rear end ratio. Jack it up and count turns of the driveshaft and tires.

If the ratio is correct, and the tire diameter is correct, then it sounds like the speedo is messed up.

 

[OneEyed]

Is there some sort of procedure to calibrate the speedometer?
The tag on the rear end says 2.76 but I will go jack it up and count it just to be sure.