Found a 87 Trans Am 10bolt 7.5, It has 26 spline axles. I was told that if I used a 28 spline mini spool I could use 28 spline axles. Does anything else have to be changed? Also, this rearend has factory 3:42 gears in it. I am going to put 4:11's in it. Would the carrier be a series 2 or a series 3.

The 26 spline carrier probably will not allow the larger 28 spline axles to pass through the side holes. You'll need a 1990+ 28 spline open carrier or just buy a 28 spline posi.

Mini spools are designed for dirt track or off road racing and shouldn't be used on the street or the strip.

The only factory 28 spline axles that will fit into that diff are from a 90-92 third gen. If you find one of those, you can also grab the 28 spline carrier. You can always buy aftermarket 28 spline axles which will be much better than factory axles.

I agree, I don't think the 28 spline axles will go into the 26 spline case. I strongly agree that a spool should not be used on the street. A 28 spline Eaton Posi would be a MUCH better choice for a street car. The 4.10 fits the same 3 series differential as the 3.23, 3.42, 3.73...

I tried swapping axles and spiders, it can't be done. You must also change the carrier.

Go with a 28 spline Eaton Posi. with 28 spline axles and a LPW Ultimate 10 bolt support cover and you wont be disappointed. By the way I chose the 3.42 gears .

Correct me if I misread that. If by "case" you mean housing, I went that route. I have a rear end from a 1983 Trans Am in my 89 RS, it had the 26 spline axles. I have since upgraded the brakes and the internals. Friends and I put in a 28 spline Eaton posi and 3.73 ring and pinion by Precision Gear. All that is original to that rear end is the housing.

Case usually refers to the carrier (posi).

My car originally came with a 9 bolt. I swapped in a 10 bolt from an '86 for better gear options. I found a 90 S10 to get the 28 spline side gears and put them into the carrier but then found my aftermarket 28 spline axles wouldn't fit through the side of the 26 spline carrier. I went back and pulled the 28 spline carrier from the S10, put the side gears back in it and put it into the '86 housing.

The case is the differential case (or carrier), not the housing. 28 spline axles will not fit in the holes of the 26 spline differential case.

Now it makes sense. I replaced the carrier with the Eaton posi.