Correct speedometer pinion

Two years ago I completed my '65 Sport Fury convertible, a 383 with a floor shift 727. TorqueFlites from 1962-65 had pinions available with teeth from 15 to 21 mounted on the end of the cable.
My car had 2.76 gears and a 17 tooth pinion, but I installed a Suregrip with 3.23 gears, and 205-70-14 radials.
I tried a 21 tooth pinion but the odometer and speedometer read about 17% over actual distance, then I installed the original 17 and a 16 pinion that tried, but both were at least 10% or higher readings. There has to be number of teeth that would fall close to actual distance.

Is there a chart that would work for TFs for those 4 years, using today's radials and gear ratios to go with the limited number if teeth available.

Thanks,

if the 21 toother reads 17% too high (double check that) then you need one with 17% more teeth so 21 X 1.17 is 18.27 teeth. so 18 teeth EDIT I did my math wrong, need 24.57 teeth. MORE EDIT if those older TF's only went up to 21 then one of those mini gearboxes (I forget what they are called) that go inline on the speedo cable to alter the ratio would be needed. I have one & if I can find a pic of it I will post it. EVEN MORE EDIT it is a "speedometer gear ratio adapter", just found em on eBay & they (on the one I saw) will select the overdriven or underdriven ratio you need. GPS would be the most accurate confirmation on what you need. MORE EDIT you want the right tooth for the odometer to read correct & most all times that will then make the SPEEDO read right but if the teeth are correct for a correct ODO reading & the speedo is off then the speedo head would need to be sent to a speedometer specialty calibration shop. For the speedo, If no GPS, on the interstate with mile marker signs (which are very accurate as far as land based signs go)) at a steady 60 MPH it should take you exactly 1 minute to go 1 mile

Somewhere there is an excel file calculator which leaves you the free to play with all values and get yourself the teeth count to let you decide, instead just a selection posted on a table.

I think is here on the tech archives. I have it saved at my PC, but I'm now on the iPad

sorry I though could attach an excel file... but not

got the link from the tech archives here

http://www.moparts.org/Tech/tech/img/AUTOMATICchart.xls

That chart is based on a 13-tooth drive gear, the pre-'66 727 has an 8-tooth drive gear.

Based on the OP's info, a 25.3" tire and a 2.76 gear, he needs a 17.6 tooth pinion so either a 17 or 18 will work but won't be dead-on correct.

If the speedo is off with the correct pinion, use the odometer instead of the speedo to gauge accuracy.

Thanks all with your input, I solved it with a conversion chart from tirerack.com: https://www.tirerack.com/tires/tiretech/45_conversionchart.jsp

Plymouth in '65 used 7.35 or 7.75-14 and 8.25 or 8.55-14, and as mentioned above the 727 used an 8 tooth drivegear. Using the Tirerack chart, I converted the 215/70R14 on my car (incorrectly stated originally that I was using 205/70R14) to 7.75-14 the original size. The factory 1965 manual calls for Green 20 tooth pinion for 3.23 gear ratio.

So now the search for a 20 tooth begins,

Thanks, Tony

if your current 21 toother is 17% too fast, just going by that actual data (current tooth count (21) & speedo 17% too fast) rather than what the charts say, I'd sure think you'd need one with 17% more teeth to slow it down that % which'd be 24.57 teeth.

I didn't do a good job reading the pinions (bad eye sight), the 21 is actually a 19 dark blue 2204358, and I started to search for a 2204359. The original in my car was a 18 tooth, 2204357, makes sense since the rear had a 2.93 gear ratio.

P/N is 2204359

Brewer's says out of stock for the 20 tooth unit.

Passon doesn't have that listing populated so call/email to see.

Used is likely the only source.

Take a look around on this web site. Lots of speedo gears listed.

https://transmissioncenter.net/home/

Manual transmissions in 1965 had a different pinion than TFs.

Didn't see any for the early TF

Only the A745 was different, everything else is the same as TF.

I stand corrected!