According to my PHS, I should have an open rear w/2.93 ratio on my 67 vert. But I can get both tires to spin when doing a burn out, so I'm thinking I may have something different. So assuming that the codes on the rear just validate the PHS info, how do I tell what I really have? BTW I don't have a tach. Thanks!

Jack it up in the back, put it in neutral, then turn the drive shaft until the wheels turn 10 times and count how many times the driveshaft turns (example 32 1/3 means 3.23, which is what I have). This works great if it is a safe-T-trac. If it's open, it gets more complicated.

If it's an original 67 rear it will have traction bar mount(s) on the axle tubes. If not, it was swapped out for another year.

Or rotate the tire one time and count how many times the driveshaft spins. ie: tire once, driveshaft spins 2.75 times then you would be at a 2.73 gear ratio. It's not exact science but it will be close. Just put a white grease pencil mark on the tire and one on the driveshaft. Have someone rotate the tire one complete revolution and count the mark on the driveshaft as it spins.

PS I can spin the tires on my LeMans with 2.56 gears, so being able to lay down some rubber doesn't really mean much when trying to determine your gear ratio...

A smart first move would be to figure out what type of rear axle you have and verify the axle codes. Takes the guesswork out of it.

If that does not work, then you can count revolutions.

it's probably due for an oil change. i'd pull the cover and count teeth

Only way to know for sure is to pull the cover and look at it. It'll either have a posi unit or spider gears. If it's a stock R&P it should be stamped with the number of teeth on the edge of the ring gear.

Thanks for the replies. The thing that puzzled me was that I thought with an open rear only one tire will spin (true?), when both did, I figured somebody made a change along the way. Guess I need to pull the cover to know for sure and as suggested change the oil while I'm at it. Thanks!

With both rear wheels off the ground an open diff will spin the tires in opposite direction and a limited slip or lockers will sping both in the same direction.

I too was able to get both tires to spin when burning out with my "original" open rear end. BUT, the tires were old and a bit hard. It wouldn't spin both with new tires.