86 Z28 w/ 305 TPI, 700R4
how do I identify the type of rear in this car? Son wants to change to a posi-carrier. I don't have a clue as what type to look for. I woulf prefer to purchase used, along with some shorter gears (3.73?). Is there a service that would allow me to find out what the spline count of the axles are? What type of carrier do i need to look for?
Thanks!

 

count the bolts on the cover

 

assuming it is stock....

it should be a 26spline 7.625" carrier. if you are planning on going with 3.73's you will need to get a 3series carrier.

 

or 3 series gears made to fit a 2 series carrier

 

or a 2series carrier, 3 series gears, and a ring gear spacer. but how did i know, someone would call me on that.

 

I also have an '86 Z28 305 TPI/700R4... There were different options, but i have a 10-bolt 7.5 inch rear, 2.73 gears w/2 series carrier non-posi, and drum brakes.

As for spline count, 89's and up have 28 spline, '88 and below have 26-spline...

You need to look for a 3 series carrier. 2 series carrier for gears 3.23 and lower (numerically lower i.e. 2.73's), anything above needs 3 series carrier.

Or you could do what ede said and get 3 series gears made to fit a 2 series carrier...

Hope that helps out a bit

 

7.5" or 7.625" doesn't much matter, the gears & carriers interchange. Most often they're referred to as 7.5". Technically, 7.5" ended in '84.

3.08 and lower is 2-series on these diffs. 3.23 and higher is 3-series. 3.23-up gears for a 2-series carrier are typically $15-25 more than 3-series carrier gears.

Some '89 and all '90-up have 28 spline axles.

Good thing this is all so straight forward...

 

Is there a number that I call get off the rearend that I could use to identify what type of carrier and axles it uses? This rearend came off a doner car, installed by a previous owner

 

you need to pull the cover and look. doesn't really matte what it left the factory with, doesn't mean it's still like it was when it was shipped.

 

There is, passenger side axle tube, stamped in, a 3 character code. Usually have to scrape off the x.x-decades of accumulated crud to see it.

The code will provide base information, but to really know you have to do what ede said.