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Offline vinnytruck

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speedo gear/drive gear
« on: September 07, 2018, 09:11:33 PM »
 Good evening guys, Could anyone tell me what color gear ( for speedometer cable) or # of teeth for a 1977 pinto C3 transmission (automatic) and do I need a drive gear to go with it. Thanks in advance VT.

Offline Wittsend

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Re: speedo gear/drive gear
« Reply #1 on: September 08, 2018, 01:20:07 PM »
Good evening guys, Could anyone tell me what color gear ( for speedometer cable) or # of teeth for a 1977 pinto C3 transmission (automatic) and do I need a drive gear to go with it. Thanks in advance VT.

It all depends on a number of factors. The tire size, the rear end ratio are all considered. So, if you see a tire size change in the near future condider that too. There are calculators out there on the internet that are helpful. This is one of many. http://www.fordspeedo.com/Calculator.html  If you don't know the number of teeth on the trasmission shaft they are typically color coded and that can easily be found - again on the internet. Hope this helps.

Offline vinnytruck

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Re: speedo gear/drive gear
« Reply #2 on: September 08, 2018, 02:03:15 PM »
wittsend, if I am mistaken, I thought that is (chart/finder) for manual transmissions. The reason I am asking is I dont have the gear to match. Any info is greatly taken.  Thanks again VT p.s. do you know why I have a lock icon on my questions???

Offline Wittsend

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Re: speedo gear/drive gear
« Reply #3 on: September 08, 2018, 04:02:25 PM »
My error on the manual trans link. Sorry.  This TCI link stated that most of the Ford Auto trans (including the C-3) speedometer gears are the same. http://www.tciauto.com/tc/speedometer-gear-calculator/

You need to:
1. Look in the transmission opening and see if you even have a DRIVE gear (on the output shaft).  If yes, note the color as it indicates the number of teeth.

2. You still need a calculator to know what DRIVEN gear (on the Speedometer cable) you will need.

You tell the Calculator what the DRIVE gear is, your rear ratio and your tire diameter (which you will have to measure). It will then calculate the number of teeth needed for the DRIVEN gear on the cable.

IF... you have no DRIVE gear then start at the middle sized gear, add in all that I mentioned above and see what DRIVEN gear it states.  If there isn't one available in that size then try a different DRIVE gear.  There are only so many DRIVE and DRIVEN gear sizes and you will need to figure out what it is you need by trial and error if the DRIVE gear is absent. BTW, if you have no DRIVE gear you will need to remove the driveshaft and rear tail housing to get a DRIVE gear on the output shaft.

On my Studebaker's GM 700R4 I not only had to change the DRIVEN gear, but it's housing too because as the number of teeth increased, the gear needed to shift location. Thankfully on the Ford I don't believe they have that need.

Offline vinnytruck

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Re: speedo gear/drive gear
« Reply #4 on: September 08, 2018, 09:00:11 PM »
THANKS WITTSEND, YOUR ALL-RIGHT KID! I will be glad when this is over. VT

Offline LongTimeFordMan

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Re: speedo gear/drive gear
« Reply #5 on: September 09, 2018, 09:24:57 AM »
The condition of the speedo is also a factor..  as they age, the magnet that drives the needle weakens and the speedo will real slow.  The odometer will be accurate but the speedo will not.I had the factory gear installed with 14 inch tires and my speedo read 50 when i was driving 60 by my gps..  the easies way to calculate is to check the odo against a gps speedo/ odo app for your phone..

The drive gears range from 16 to 23 teeth. 

Mine had 19 and was 50/55 = .90 so i multiplied 19 x.90 to get 17 teeth which made my odo axactly accurate as measuered over 100 miles..   however my speedo still reads slow by about 5 mph..

The only way to get the speedo accurate once you have the correct gear for the odo is to have the speedo remagnetized by a speedo service place. The last time i had one done it cost like $100. I now just use a gps speedo app on an old, spare android phone.

The one I use is TripMaster by DS Software.. it also has an odometer that will record  cumulative mileage.. and if you have an old.android phone available the gps will work even if you dont have it ac5ivated for data..
Red 1973 pinto wagon DD, SoCal desert car, Factory 4 speed, 3.40 gears, Stock engine, 14" rims and tires, 60 K original miles

Offline LongTimeFordMan

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Re: speedo gear/drive gear
« Reply #6 on: September 09, 2018, 09:57:51 AM »
Heres a source for ford speedo gears..

https://www.transmissioncenter.com/shop/ford-automatic-transmission-speedometer-drive-gears/

They have a lot of info about  stock ford gears.

To properly calibrate your speedo you need a reference like a gps speedo/odo app for your phone to get an accurate reference. I posted a info about one i use above.

The basic concept is that if your speedo reads slow compared to your gps speedo app you need a gear with fewer teeth to make it spin faster..

If you know your mileage as measured with gps app and your odo reading from your mechanical odo you divide mechanical odo by gps odo then multiply by number of teeth on your existing gear to get correct gear teeth.

Count teeth on existing gear.

Drrive 100 miles with gps, read mechanical odo.

And existing gear is 19 teeth ( pretty common)

If mechanical reading is like 90, divide 90 by 100 get .90,

Multiply 19 x .9 and get 17 which should give you correct odo. However your speedo may still be off due to weakened magnet in speedo head.
Red 1973 pinto wagon DD, SoCal desert car, Factory 4 speed, 3.40 gears, Stock engine, 14" rims and tires, 60 K original miles

Offline vinnytruck

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Re: speedo gear/drive gear
« Reply #7 on: September 12, 2018, 10:05:34 PM »
THANK YOU ALL, WILL BE TESTING THIS WEEKEND. VT