I changed my hogs head to a lower ratio. Now (as expected) my speed is off. I have been told that 1 tooth equals about 5 mph. But at what speed? When traveling at 50 mph, I show 65 mph. I have a 18 tooth gear. What do you guys suggest?
21 tooth is what I have done - red gear for manual and purple for automatic. Of course it all depends on what parts you have, gear ratio, tire size, ect. But with the speed off that far, I think a 21 will do it. Check this site out - there is a link to a calculator part way down the page. Hope this helps ............ http://www.transmissioncenter.org/Ford_Speedometer_Gears.htm
Thanks for your help. I have emailed the site. The only problem with the calculator is I do not remember what the rear end ratio is.
then...how do you know that it changed...may just be your speedo is reading incorrect... spin a rear wheel and count how many times the driveshaft turns to 1 revolution of the wheel...
Your 18-tooth gear is turning 30% too fast. You need to add 30% more teeth to slow it down to the correct speed. 23 teeth, if there is such a thing.
Depending on what transmission you have (auto or man), you may also have to change the Drive Gear on the output shaft too, which would require removal of the tailshaft housing. Like the speedo gears, they come in 3 or 4 different tooth count and are colour coded, green, pink, black, etc., I can't remember all the different ones.......but as mentioned in an earlier post, you have to figure out what rear end ratio you have first and go from there. the combo I had to use with my 3.70 gears was 6 tooth Drive Gear and 18 tooth speedo gear with P235/60 14" tires.
Your gear oil probably needs changed anyway. Pull the center-chunk and count the teeth on the ring & pinion. Then you'll know the exact gear ratio.
The center I put in was from a Pinto I believe it was a 328? The speedo changed at that time. BM- you make sense about the 30%. I think I will try a 21 tooth.
