When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have an 83 F250HD with a Dana 44 and a Dana 61, 3.54 ratio. It has the C6, auto, Tires are 285/75/16.
The drive gear in the case is a green color (6 tooth).
When I bought the truck it had a yellow (18 tooth) driven gear on it, I bought a green one (17 tooth) in the hopes that it would correct the speedometer but it didn't. I think today it said I was going 25 but I was going like 32. Maybe I went the wrong way?
On a similar note the yellow gear has a shorter shaft protruding from the end of it than the new green one does. The new green one fits, and lot of the noise that I was getting from the speedometer in the cab is gone.
I have an 83 F250HD with a Dana 44 and a Dana 61, 3.54 ratio. It has the C6, auto, Tires are 285/75/16.
The drive gear in the case is a green color (6 tooth).
When I bought the truck it had a yellow (18 tooth) driven gear on it, I bought a green one (17 tooth) in the hopes that it would correct the speedometer but it didn't. I think today it said I was going 25 but I was going like 32. Maybe I went the wrong way?
On a similar note the yellow gear has a shorter shaft protruding from the end of it than the new green one does. The new green one fits, and lot of the noise that I was getting from the speedometer in the cab is gone.
Funny how these topics come in bunches
To calculate the correct driven gear. you need The gear ratio of the rear end. Tire Revolutions per mile and the number of teeth on the transmissions speedo drive gear
The formula for calculating the correct driven gear number of teeth on the speedo cable is as such.
# DRIVE TEETH x AXLE RATIO x TIRE REV. PER MI.
_____________________________________________ = # DRIVEN TEETH
1001
For example lets say the number drive teeth on the trans speedo drive gear is 7 and lets say tire diameter is 28.89"
So with that
To calculate tire revs per mile
20168
_______________________________ = REVIOLUTIONS PER MILE
TIRE DIAMETER (in inches)
Tire Revs per mile 20168 / 28.89= 698.096 And round to 698 Revs per mile.
So knowing that
we can use the other formula
7 x 3.92 x 698 / 1001 = 19.13 And to round it to 19 So would need a driven gear with 19 teeth.
You have the info you need you just need to run the calculations using the above formula.
I have an 83 F250HD with a Dana 44 and a Dana 61, 3.54 ratio. It has the C6, auto, Tires are 285/75/16. The drive gear in the case is a green color (6 tooth).
When I bought the truck it had a yellow (18 tooth) driven gear on it, I bought a green one (17 tooth) in the hopes that it would correct the speedometer but it didn't.
I think today it said I was going 25 but I was going like 32. Maybe I went the wrong way?
Adding teeth slows the speedo down, subtracting teeth speeds it up. You subtracted a tooth by going from an 18T to a 17T DRIVEN gear, speeding the speedo up.
So 7x3.54x630/1001 is 15.59. Should I round up or down?
That is a crap shoot 15.59 is closer to 16 than 15.59 is to 15. Round up the speedo to read bit low round up round down it will read a bit fast Any how I think you re stuck with the 16 tooth gear as IIRC 16 is the lowest tooth number driven gear available (ND will know for sure) but 16 is readily available. Rounding up your speedo will read about 2.5% lower than actual. So at 50 MPH it will be the speedo will read 1.25 MPH lower than actual. at 75MPH it will read about 1.87 MPH lower than actual.
So when calculating fuel economy with miles traveled and fuel used remember to add on the 2.5%
Some cars and trucks I have driven have been dead on, but most of them have been a little conservative from the factory, reading a couple miles per hour faster that I was really going. That can be a good thing when you go through a speed check on the side of the road.
My wife's honda is about 2 mph fast, my 99 Tahoe is 3 mph fast, and they are all original with the correct size tires. By fast I mean the speedo reads fast, which means the vehicle ends up going slower. My 09 superduty at work is dead on correct. My 86 Ranger is all over the place depending on the outside temp(cable problems).
So I got the 16 tooth gear installed and it's much better as far as the speed goes but now my speedometer is really loud again. I think the longer shaft makes the difference. Here's a picture so you can see what I mean.
Does anyone know where I can get one with the longer shaft?
I have an 83 F250HD with a Dana 44 and a Dana 61, 3.54 ratio. It has the C6, auto, Tires are 285/75/16.
The drive gear in the case is a green color (6 tooth). Trans has been swapped!
When I bought the truck it had a yellow (18 tooth) driven gear on it, I bought a green one (17 tooth) in the hopes that it would correct the speedometer but it didn't.
I think today it said I was going 25 but I was going like 32. Maybe I went the wrong way?
C6 = 1966/72: DRIVE gear on output shaft replaceable. 1973 and later: DRIVE gear not replaceable, as it's made as part of the output shaft!
Deduct teeth to speed up the speedo, add teeth to slow it down.
Parts catalog does not list P-Metric radials, so I cannot give you the correct DRIVEN gear part number/tooth count/color.
So I got the 16 tooth gear installed and it's much better as far as the speed goes but now my speedometer is really loud again. I think the longer shaft makes the difference. Here's a picture so you can see what I mean.
Does anyone know where I can get one with the longer shaft?
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.
