i've got an 86 gt vert with the original rearend. is there a way to tell if i have 2.73's or 3.08's? i bought the car new in 86, but have no idea. its a 5 speed, and it tachs 2200 rpm's at 85 mph in 5th gear. i've read that 3.08's were an option
Another method you could use to find out what gears you're running (short of counting pinion and ring gear teeth) would be to mark the driveshaft and a rear tire, and with the car on stands, count the number of revolutions of the driveshaft in relation to one full revolution of the tires. An example would be, with 3.08 gears, you'd have approximately 3 full revolutions of the driveshaft for one full revolution of the tires.
Look at the bolts that hold the differential cover on. One of them should have a small metal tag on it. Look for one of these codes:
2L73 or 3L08
The "L" means "Locking", and you can guess what the numbers mean.
The tags are often lost when you have maintenance done on the rear end (fluid changes, etc.), so then you'd have to rely on the door tag. If you hadn't owned the car its whole life, then you'd have to do the tire/driveshaft rotation count to be sure that someone didn't swap out gears.