I have a rear end that came out of a 83 S-10, How can I tell if it's posi trac? I know it has 3.42 gears.

 

If you look into the center of the carrier, and see four little gears (two on the sides, one up top and one on the bottom) and a long pin going down the center only, its an OPEN carrier. If it has other stuff in there as well, its some sort of limited slip.

 

count how many times the drive shaft turns in respect to one revolution of the rear wheels . example. 3.5 turns of the drive shaft to one complete revolution of the rear wheels would be a 3.50 to one gear ratio. So if it goes a little less than 3.5 times that would be a 3.42. If it goes like 3.25 times around it would probably be a 3.23 gear ratio. If it goes like 2.75 times it would probably be a 2.73 gear ratio. Hope you can figure the rest out. If the wheels turn the same direction with the rear jacked up and the car in neutral then you can be pretty sure you have a limited slip unit of some sort. If the drivers side goes forward and the pasenger side goes reverse you have an open rear. Make sure you test this by turning the driver side forward. Goodluck