My 83 GSL needs a new rear differential.
I found two on eBay. A 26 & a 24 spline.
Anyone know off hand what I should have?

 

83 is a weird year since they switched to large axle mid-year. Its best to check if you have a large or small axle.

 

Where would I be checking?
Outside OD?
I don't really want to pull my axle.
Just have the diff installed.

 

Easiest way is to remove the gease cap from the front hub. Look at the spindle nut. If its a regular nut, its a small axle. Large axle spindle nut look like this one.

 

My nut Looks like this w/ a foil castle nut & pin.
Assuming I have a small axle then.

Need to pull the trigger on a differential.

 

..if the driveshaft to diffy flange bolt has a nut on the other side, it is a large axle. Small axle has a threaded diffy or pinion flange.

 

I've nuts on the front side, motor side.

 

in 83 there were both, i have an early 83 axle that has the late model non-threaded pinion flange that has a square bolt pattern and requires a nut/bolt combo to attach the driveshaft, yet it is the small spline/small bearing axle

 

Thatt was onmy first post that an 83 has mixed up parts and the one above ur post is based on a typical scenario for parts identification.

 

Just an update & for future reference, it was 24 spline.

All is well in my world - my FB runs & drives better than I've ever known.

 

83 will have small splines (like early) and square driveshaft flanges (like late). The only midyear change in that timeframe was the '84 models which had fine-tooth gearsets for a few months. (3.933 instead of 3.909, and some similar difference for GSL-SE)