ok i have a 89 formula 305 tbi with a 10 bolt pattern on the rear... can anyone tell me what rear end i have.. ohh its automatic... did any of this type of rear-end come with posi?? thanks in advance for your help
Corey

It's more than likely 2.73:1. Posi was an available option
If when you drive on the hiway @100Kph in *drive*(not OD), and your tach reads right around 2350/2400 rpm, you have 2.73:1 gears.

at about 100mph with the 2.73 i run around 3250rpms....115 still isnt yellow lined in drive...