Using the archives and some links I was able to determine how to calculate what speedometer gear is needed to recalibrate the speedometer when changing to lower rear gears. However, I've run into one problem with the information that I've found. Some sources say the output shaft gear on C4 transmissions (the drive gear) can be 7 or 8 teeth while other sources say 8 or 9 teeth. See this link for the 8 or 9! http://429mustangcougarinfo.50megs.com/speedo_gears.htm Anyone know for sure?
There are 7, 8 and 9 tooth output shafts for C4, C4s and C5 transmissions..... It has been my experience that the 8 is most common and 7 is least common..... The only way to know for sure is to remove the tailshft housing and count them.....
71 Gold, tried that but difficult to tell. Even tried counting by "feel". According to my calculations with 3.80 rear gears, 7 drive teeth and 245 60 15 tires I need a 21 tooth driven (speedo cable) gear. It currently has a 20 tooth driven gear. But, the speedo was waaaaay off and I don't think one tooth on the driven gear is enough to compensate for a 15mph difference at higher speeds. It must be an 8 tooth drive gear which would need about a 23 tooth drive gear. They are available but don't last long! Any thoughts?
They are more like a twisted spline about an inch long and are offset in the hole, very hard to see.....
