Just installed my 3.73's.  Wanted to know what gear i need to calibrate my speedometer, and if anybody has done the install for the gear and if so, a how-to and how hard it is.  

The Install is real easy the VSS is just helt on by a single screw on the transmition then a gear clip connects the driven gear

since im taking it you have a 88 mustang by your name the internal gear in your transmission is a 7tooth so you would need a 21 tooth gear i believe for a 3.73 rear

it also depends on wheel heigth  

Thanks for the info, i'm probably gonna order the gear monday.  

same problem here, I have 18'' chrome cobra wheels with 255/35 up front an 285/35 in the back.  Running 355 ford gears. Thats no problem.  I bought a rebuilt t5 transmission and don't know what year stang it came out of.  So is there any wany I can find out w/o taking the tranny out.  I need to know before I buy ny speedo gear because I don't know if I have a 7 or 8 tooth drive gear.  Good luck  

just unscrew the vss on the side of the transmition and then look inside the hole to see what color the internal gear is. You can figure out how many teeth are on it by the color.