Sanity Check - 8.25 27 spline to 29 spline

I think I have a solution that will work for me. Just wanted to see if I have missed anything.

I have a 29 spline 8.25 with 3.55 gears in my rig right now.

I have a 27 spline 8.25 with 4.10 gears sitting in my garage. (and a matching D30).

I have an Aussie in the 29 spline 3.55 as well.

I plan to swap the 29 spline carrier (with the Aussie) into the 8.25 with 4.10 gears. I know I will need to swap the ring gears and by extension pull both carriers and deal with the associated adjustment and preload, etc. at reinstallation.

Other than doing the above, I plan on replacing the bearings and seals in the 4.10 axle with ones for the 29 spline shafts. Am I missing anything? Based on my research, this seems like it will work and nets me better gearing and I get to keep my Aussie and 29 splines. I am assuming that the 8.25 housings are the same and can accommodate these changes.

Can anyone confirm or deny?

The parts should all transfer fine. The challenge will be transferring the gear set such that it runs quiet. Having broken in on one setup it may be noisy when swapped into another setup.

Chances are the gears will be noisy, it's difficult to reset used gears and have them run quietly.
If it is a DD, and you care, I would consider a new ring and pinion.
I assume you have the knowledge and the tools to do the job properly.

Running thicker diff fluid might help but you're still going to hear it

Use the 27 spline 8.25 with 4.10 gears sitting in your garage and the matching D30.
Sell 29spline aussie and buy the 27spl version if you really need it. The 27 spline 8.25 isn't the ticking time bomb the internet wants you to believe it is.
Unless you insist on replacing the carrier/pinion bearings and seals in the 29spl 8.25. You'll have to reset the gears after that anyway and just spend the extra $200 or so on new gears.

Or, if you're in south east Virginia, sell me those 4.10 axles.

Am I missing something? Why not swap the 29 ausie and shafts into the 4:10 geared housing? Or is this a full case locker?

I do not believe a 29 spline lunchbox will fit in a 27 spline carrier. Or perhaps 29 spline axles will not fit in a 27 spline carrier. Whatever it is, I think a lot of folks would be really happy if it worked, but I think it has been tried and is a no-go.

I have converted 27 spline to 29 spline before.

The ONLY differences are the carrier and its internals & the shafts. The side gears/spiders and cross-pin are different.

To use the 29 spline Aussie you will need to swap the 4.10's on the 29 spline carrier, verify the pinion depth and set the backlash, and install the shafts.

All seals & bearings are the same.

If you're doing the work yourself, the most important things I can tell you is to make sure you tighten the side adjusters until they stop turning. 75 ft-lb is considered a starting point. It may be 125-150 ft-lbs before they don't move. Also, collapsing the crush washer can be difficult because of the high torque (think 300+ ft-lb) and then you need to measure the rolling torque and make sure its in spec. You can use an impact wrench if you're careful in lieu of long breaker bars, pipes, 3/4" breaker bars, or torque multipliers.

So the 8.25 27 spline carrier is different than the 29 spline carrier or is it the gears that need a different carrier? Which is common to have a carrier break I forgot about that.

Ghost said:

So the 8.25 27 spline carrier is different than the 29 spline carrier or is it the gears that need a different carrier? Which is common to have a carrier break I forgot about that.

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Different carrier all together. The spider gears, or in this case, the 29spline locker, won't fit in the hole in the 27 spline carrier.

The ID for the axle shafts is too small on the 27 to fit 29 shafts.
One could machine this, IIRC, though

I've only sold these things never upgraded them. Good info to know.

Not a DD, have someone lined up for the gear adjustments. Will go with thicker diff fluid as well.

Or maybe I'll just stick with 27 spline and sell the Aussie ...

Thanks for the feedback.

Ghost said:

So the 8.25 27 spline carrier is different than the 29 spline carrier or is it the gears that need a different carrier? Which is common to have a carrier break I forgot about that.

Click to expand...

As the others said, the carrier and shafts change, not the gears. The carrier break is at 2.72 so in the Jeep world we don't run into it.