How to identify gears when not stock?

Hi guys,

couldn't find answer with "search" so here goes. just got a 93' Formula Firebird. previous owner said to his knowledge that car is stock except for rear gears. the speedo is off by 10 to 15 mph, if you are going 60, you are really going 45. going to go out an compare to wifes jimmy to make sure of how much mph is off. is there a way to find out the gear ratio? i read on a forum there was a way to spins wheels and watch drivshaft turn to come up with ratio, but can't locate post on how to do this. (at least i think this post had something to do with question). i believe the tranny is an 4L60 or 4L60-E, not sure. if at a stop, and drive normally 1st gear hits and then 2nd hits like a 1/2 second later, almost like you could start off in 2nd. could this have anything to do with speedo or gears, or is this the way the tranny is suppose to act? any and all help is needed.

thanks,
Gary :confused:

You can mark the driveshaft and wheel and count the turns.
I would rather pull the cover and check it. When you roll the ring gear around there should be a little number and a big number stamped into the edge of the gear, divide it and thats your ratio. Or count the teeth on each and divide.
I would pull the cover to also double check torque on the bolts and make sure the contact pattern is good. Especially if you dont know who did it, what ratio you have, if its a good set or cheapo gears or anything else kind of important about it.....

I got an s-10 truck once that had a pinion seal leak, pulled it apart to find a miss matched gear set. I thought it making noise because it was ready to scatter, till I tore it down and found that. People do some stupid things...

Ohio,
thank you for the advice and info. the car was well taken care of, just would like to know what parts have been altered and with what. will pull the cover and double check gears. thanks again.

Gary