3.55 speedo gear

[87WhiteStang1]

how many teeth on the speedo gear when you put 3.55's in?

 

[FoxChasis]

Assuming you have an '87 Mustang, and the transmission is the factory original one with the factory original speedometer drive gear, and the tires are the factory original tires or the same size, you need a 20T gear, Black for a manual or Orange for an auto.

black 20T = Ford part number C1DZ-17271-A
orange 20T = Ford part number C8SZ-17271-B

If my assumptions are incorrect, you need to spell out exactly what car you have and what exactly has been changed in the transmission and tire areas.

 

[87WhiteStang1]

its actually for my friends 91 lx its the stock transmission with 3.55 rear and draglites in the back tires are slightly bigger

 

[faststang90]

black 20T = Ford part number C1DZ-17271-A is the one for a 5 speed tranny. the ford book says that u can not get a right speed if u r using a bigger tire but that # is for 90-95 t5s

 

[FoxChasis]

Sorry, 20T is not right for 3.55 and a '90-'95 V8 T-5s. That would be 23T, and that gear is not a Ford gear and it is crap.

mid '89-'95 = 8T drive gear
'83-'mid '89 = 7T drive gear

7 x 3.55 x 810 / 1000 = 20T
8 x 3.55 x 810 / 1000 = 23T

810 is the approximate RPM of stock tires.

Can't tell you what gear is required if you don't tell me what the RPM (or height) of the now-taller tires are.