We have 4:10's in our Mav which off course throws the speedo way off. We also have a C4 which doesn't have that easy nylon gear swap like late model Ford trannys. Has anyone tried one of these... http://www.transmissioncenter.org/speedometer_gear_housing.htm (scroll down a little to the fourth photo - speedometer gear ratio adapter)
All you have to do is remove the hold down bolt and clamp, pull the speedo end out of the transmission, pop off the "C" clip, remove the old gear and install the new one. Install the "C" clip, push the cable end back in the transmission and replace the clamp and bolt. I don't understand what is hard about changing the gears?????
The first thing to know is how many revolutions the tires make in one mile. To calculate this, measure the diameter of your tires. 26" is about average for F60-15's or 245-60-15's. Multiply this measurement (26") by pi (3.1416). This will give you the circumference of the tire. Next, divide one mile in inches (63360) by the circumference of tire (63360 divided by (26 x pi)=776). This equals the revs per mile of the tire. Now multiply this number by the rear axle ratio to give you the number of drive shaft revs per mile (776 x 3.91= 3033). Next, divide this number by 1000 (3033 divided by 1000 = 3.033). This is the ratio of transmission driven/drive gears on speedometer cable you will need in this case use a driven gear with 18 teeth and a drive gear with 6 teeth (18 divided by 6 = 3.0). This is the best choice which yields a 1.1% high error which means your odometer unit indicates 1.1% greater than actual or 10.11 for an actual 10.0 miles. If you are using the Ford adapter/reducer (reducer was factory equipped on cars with 3.91, 4.11 or 4.30 rear axle ratios), multiply the number by 0.75 (3.033 x 0.75=2.274). This is the driven/drive ratio you need. A 3.75% error (i.e., a 0.375 mile error in 10 miles) is considered acceptable by design. Use the next higher number of teeth for your 4.62 gears.
What you talking about Willis!? lol Do I measure the tire say from top to bottom? Across one side to the other on center?
So back to the original question: has anyone used this company's part? I think I'll give it a go...when my bank account recovers from the car purchase...
I have not. I would have thought PaulS would have been the one that has come across it if anyone as he is a trans guy. Sorry I was a contributor in steering off a bit.
Similar devices are used by shops that tune speedometers for cars with modified drive trains. They use smaller planetary gear drives but the effect is the same.
