Anyone know what size rear(is it the 7.5?), gears, and spline that came in a 1985 iroc 305 TPI?
(I think its 3:42? and its a non-posi 10 bolt) Also, I would like to upgrade to 3:73's and a posi. What do I need to buy to do this and should I replace the axles to a larger spline(if possible)I'm not very familiar with rears.
Thanks in advance

 

can you get the axle code off the front passenger side of the axle tube... take a wire brush with you

 

They are 28 spline axles and it wouldn't hurt to upgrade them to better ones if you plan on putting out some power. Moser engineering sells some and I think Strange sells them too. In 85 the size of the rear is 7 5/8. It looks like you have 3.42 gears if it has the G92 option, or 3.23 gears standard. To upgrade the rear to 3.73's and a posi you will need to get a 3 series posi carrier (i think), a set of gears and an installation kit. I would reccomend the SLP posi unit, or an eaton or auburn unit. For the gears, I'd say Richmond is probably the best, but you can find others that are decent. Whoever you buy the gears from will most likely also sell an installation kit. You will have to have them installed (unless you're a GM tech) because they have to set backlash and shim it. That should about cover it, I don't know a whole lot about rearends, but that's what I've picked up from being around here, most of the info should be right, but I can't gurantee it.

 

Actaully you have 26 spline axles in your 85, not 28 spline. If you upgrade to a zexel posi, then you have to get different (28 spline) axles from a 90 or newer rear. They can be found used, but in some areas of the country they are pretty rare. I have any extra set just because.

Spend some time searching the word "zexel" and "gears" in this forum. You will get all the answers you need and then some.