Can any1 tell me the number of teeth needed for a 380 rearend with 28in rubber. Also its a C4 trans. greatly appreciated . TTFN RON
Thanks Mavaholic and Scooper for all of your help. Daydreamer, if you can get a copy of the December 2005 Mustangs and Fords issue, it will give you all of the formulas needed to calculate what you need. The article may be on their website by now, the name of the article is Geared to Go.
thanks for the info but getting a mag issued from 2005 is extremely difficult in Ontario. I will c what the dealers have to say or maybe some1 has the formula handy . TTFN Ron
If your speedometer reads high, you need a drive gear with more teeth. If your speedometer reads low, you need a drive gear with fewer teeth. A drive gear with 18 teeth is going to turn faster (and read faster) than a drive gear with 21 teeth. If your speedometer is reading 10 mph too high and you have an 18-tooth drive gear, you need a 20-tooth drive gear. The highest number of teeth available on a Ford speedometer drive gear is 21. After that, you must run a reducer that was common to Fords with 3.89:1, 3.91:1, 4.11:1, and 4.30:1 rearend gears. Taller tires will make the speedometer read lower. Shorter tires will make it read higher. Even tire inflation can affect speedometer reading. Here is some good reading. http://429mustangcougarinfo.50megs.com/speedo_gears.htm
That's a manual trans gear. The automatic uses one with a longer tip. Color has nothing to do with the transmission it goes with.
28 x 3.1416 (Pi) = 87.96(this is the circumference or distance around the tire in inches) Divide that into 63,360 (inches in one mile) to get revolutions per mile. 63,360/87.96 = 720.3 . There are seven drive teeth on a C-4 tailshaft, mulitiply that timee the gear ratio ( 7 x 3.80) then times the tire revs per mile (7 x 3.8 x 720 = 19,152 ) then divide by 1000 to get the driven gear tooth count. 19,152/ 1000 = 19
According to the chart it does. Ron, all the formulas along with the chart was published in the May/June 2007 issue of Short Horns.
speedo gear Thanks Baddad457 for the formulae and the figures.greatly appreciated. Dennis, thanks for that info. I forgot and I will immediately look it up.
