I have 8.25 with locker in it(welded) I run 35s and i was wondering if it will hold up? I am building a rock crawler so I don’t really want to break it on the trail. Also have been thinking about going to a 8.8 but if the 8.25 is good then I’ll stick with it.

You would gain very little in strength switching to the 8.8, it's not really worth the trouble or cost. My 8.25 has been holding up fine with 4.56 gears, and a Spartan locker on 35s, but I don't do any extreme rock crawling, mainly just mild trailes and mud. I have had it bouncing and spinning all 4 tires a few times, pulling full size trucks out of the mud, and everything held up fine. If you need more than a 8.25 can offer I would suggest going to a Ford 9" or even 1 ton axles depending on what you want to do.

No point in going to a 8.8 from a 29 spline 8.25. I run a 8.25 with 4.56s, aussie locker, ruff stuff cover, and it has never complained about 35s on the rocks.

The 29 spline 8.25, Dana 44, and Ford 8.8 are all in the same neighborhood as far as strength goes. There's no point swapping one for the other. If you have a 27 spline 8.25, I have heard that you can upgrade it to 29 spline by replacing the differential carrier and swapping in new shafts. But someone who knows for sure should verify that.

If you want to do an upgrade, look for a big bearing Ford 9" that you can truss and put 35 spline axles into. Dana 60's are good, though some are better than others depending on what it came out of. But most of them from the factory are pretty wide for an XJ.

Aftermarket axles (Ford 9", Dana 60, even a Dana 44 based on the new generation 44 out of a JK) are all upgrades but they will drain your wallet pretty fast.

However, a 29 spline 8.25 on 35's will probably last for a long time unless you really beat on it with lots of throttle and speed.

How can I tell if mine is 29 spline?

If yours is a '98 it's a 29sp.. or you could just pull the shaft and count the splines

The 8 25 is plenty strong. A wheeling buddy of mine has a 29 spline 8.25 with stock shafts on 35s & beats on the thing every chance he gets. Zero issues.

I'm running a 29 spline 8.25 out of a 97 with factory 4:10 gears. I'm only running 33's right now, but I added a Aussie locker and "Solid" diff cover and have had no issues what so ever...... If I was going to go through the process of swapping it out for a upgrade, I would do a Ford 9" if anything.

Years ago we swapped out my axle with a 29 spline from a later model Cherokee, never had any issues with it since. Figured I'd have to swap to tons before I'd break it

On 35s you might be OK but my 39.5 swamped would break stock axles every time and one ring and pinion one locker the axle parts would break before the rest of the drive train

I broke a 27 spline 8.25 shaft was able to drive home because i have disc brakes. Upgraded to 29 spline and its been bullett proof since.

Im running 4.88 gears. Welded spiders and 35s