I have a question I don't know much about defs and gearing. My jeep has 27 spline shafts and I was going to upgrade to 30. What would the difference be and can i use 30 spline shafts with stock gearing?

 

You would have to get a whole new carrier with 30 splines.

 

ok ty

 

What axle or axles, D/30, D/35 yes you can install 30 spline shafts. The D/30 is worth the time and money spent to do the upgrade the D/35 isn't. You will need to replace the spider gears or install a full carrier locker like a Detroit.
If you are talking about a Chrysler 8.25 you can upgrade to 29 spline shafts.

These upgrades will be an increase of about 25-35 in strength.

 

So I want to get a locker, does that take the place of the stock carrier? Can I just get a Locker for 30 spline axles?

 

Like rock toy said. Detroit, You won't regret it.