Speedo Gear Question
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Elder User
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Speedo Gear Question
I resently aquired a new to me 68 F350 from Ebay. I am pretty happy with the truck but have determined that my speedo is way off. Orginally the truck had 3:73 gears in the rear. At some point the frame was streched and now has 4:11 gears. I have not had anyone follow me but I think when it says I am doing 55 I am doing about 37. The tires are 7.50 16's. The tranie is the orginal warner 4 speed. Can anyone tell me what new speedo gear I need and where I can find one? Thanks
Lead Driver
Joined: Jan 2003
Posts: 9,893
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From: Ohio
Well, you need to pull the speedo cable out of side of tranny and inspect the nylon gear on the end of cable. Count the teeth(sometimes they are actually marked ie:17, 18, 19). Once you figure out what you have, using some math we can calculate the teeth needed to slow the speedo down some.
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
Usually when you ADD gear ratio...you need to ADD teeth to slow the speedo down. It's the difference between DRIVE and DRIVEN gear as the ratio. You want the DRIVE gear to turn MORE times before turning the DRIVEN gear. Clear as mud?
That is why back in the day, they also had a couple different driven gears(one inside tranny), as you couldn't change the drive gear enough to compensate for the 4.10/4.30 drag pack gear ratios.
That is why back in the day, they also had a couple different driven gears(one inside tranny), as you couldn't change the drive gear enough to compensate for the 4.10/4.30 drag pack gear ratios.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 787
From: Simi Valley, CA
Driven Gear = on the end of the speedo cable.
Drive gear = on the output shaft of the transmission.
ALL the plastic (nylon) driven gears are still available from Ford: 16-17-18-19-20-21 teeth are available.
cbfomoco: 1968/70 F350 / Warner T-18 / 4.11-1 / 7.50 x 16 tires.
16T NYLON driven gear = CODD17271A replaced by > > CODZ17271A / Available from Ford.
MSRP: $3.04 / FTEpartsguy.com price: $2.18
6T NYLON drive gear = DOTZ17285A / Available from Ford
MSRP: $48.60 / FTEpartsguy.com price: $34.99
NOTE: Some of these early 4 speed transmissions also used either fiber or iron driven gears, steel drive gears.
With 3.73's, the driven gear is 17T, the drive gear is 7 teeth / With 4.11's, the driven gear is 16T, the drive gear is: 6 teeth.
btw: Thank you for listing all the pertinent info (I wish more peeps did when asking questions). Without the tire size/rear axle ratio, I could not have typed the part numbers above!
Drive gear = on the output shaft of the transmission.
ALL the plastic (nylon) driven gears are still available from Ford: 16-17-18-19-20-21 teeth are available.
cbfomoco: 1968/70 F350 / Warner T-18 / 4.11-1 / 7.50 x 16 tires.
16T NYLON driven gear = CODD17271A replaced by > > CODZ17271A / Available from Ford.
MSRP: $3.04 / FTEpartsguy.com price: $2.18
6T NYLON drive gear = DOTZ17285A / Available from Ford
MSRP: $48.60 / FTEpartsguy.com price: $34.99
NOTE: Some of these early 4 speed transmissions also used either fiber or iron driven gears, steel drive gears.
With 3.73's, the driven gear is 17T, the drive gear is 7 teeth / With 4.11's, the driven gear is 16T, the drive gear is: 6 teeth.
btw: Thank you for listing all the pertinent info (I wish more peeps did when asking questions). Without the tire size/rear axle ratio, I could not have typed the part numbers above!
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Elder User
Joined: Aug 2005
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So I need both to make it right? Thanks
Driven Gear = on the end of the speedo
cable.
Drive gear = on the output shaft of the transmission.
ALL the plastic (nylon) driven gears are still available from Ford: 16-17-18-19-20-21 teeth are available.
cbfomoco: 1968/70 F350 / Warner T-18 / 4.11-1 / 7.50 x 16 tires.
16T NYLON driven gear = CODD17271A replaced by > > CODZ17271A / Available from Ford.
MSRP: $3.04 / FTEpartsguy.com price: $2.18
6T NYLON drive gear = DOTZ17285A / Available from Ford
MSRP: $48.60 / FTEpartsguy.com price: $34.99
NOTE: Some of these early 4 speed transmissions also used either fiber or iron driven gears, steel drive gears.
With 3.73's, the driven gear is 17T, the drive gear is 7 teeth / With 4.11's, the driven gear is 16T, the drive gear is: 6 teeth.
btw: Thank you for listing all the pertinent info (I wish more peeps did when asking questions). Without the tire size/rear axle ratio, I could not have typed the part numbers above!
cable.
Drive gear = on the output shaft of the transmission.
ALL the plastic (nylon) driven gears are still available from Ford: 16-17-18-19-20-21 teeth are available.
cbfomoco: 1968/70 F350 / Warner T-18 / 4.11-1 / 7.50 x 16 tires.
16T NYLON driven gear = CODD17271A replaced by > > CODZ17271A / Available from Ford.
MSRP: $3.04 / FTEpartsguy.com price: $2.18
6T NYLON drive gear = DOTZ17285A / Available from Ford
MSRP: $48.60 / FTEpartsguy.com price: $34.99
NOTE: Some of these early 4 speed transmissions also used either fiber or iron driven gears, steel drive gears.
With 3.73's, the driven gear is 17T, the drive gear is 7 teeth / With 4.11's, the driven gear is 16T, the drive gear is: 6 teeth.
btw: Thank you for listing all the pertinent info (I wish more peeps did when asking questions). Without the tire size/rear axle ratio, I could not have typed the part numbers above!
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 787
From: Simi Valley, CA
I'd try the driven gear first, since it's cheap and EZ to replace.
Removing that drive gear on the output shaft is a PITA. You have to remove the driveshaft and the extension housing (tailshaft housing) to get at it.
Removing that drive gear on the output shaft is a PITA. You have to remove the driveshaft and the extension housing (tailshaft housing) to get at it.
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