D30 Upgrade with 31-inch tires

Vehicle: '87 4.0 Auto, NP242, 31" tires.

I’m about to regear my d30 and will need a new carrier to get down to a 4:10 ratio. Before I pull the trigger on a locker for the front axle I’m just trying to get a few things clear in my head to decide whether I should buy a 27 or 30-spline carrier.
Is the 27-spline option strong enough (considering I’m running 31’s and don’t ever plan on going bigger) to reliably operate with a locker, or is the added hassle related to the extras needed to run 30-spline worth the extra expense?
As I understand it, converting to a 30-spline axle set requires adding an aftermarket outer/unit bearing, and swapping out the brake rotors for Wrangler rotors (presumably due to clearance issues). Are there any other necessary changes?
Also, is the aftermarket the only place to get a 30-spline unit bearing for a D30? (i.e. Does another Jeep like a YJ or TJ run a D30 with 30-spline outer bearings as stock that will work on a XJ D30?)
From reading the Dana 30 Tech writeup that Crash did, (http://www.naxja.org/forum/showthread.php?t=70422&highlight=axles+for+rocks) I understand that putting a 30-spline axle in will leave the R&P as the weak link in the system. Am I incorrect in thinking that is the better option for cost of replacement as well as trail driveability in the case of a failure?

That's a debatable point. Some say it's best to let the shaft be the weak link others say let the R&P be the weak link. Look up the Super 30 kit.

i think the tj line of thinking would work you would just need to get 00-06 tj d30 unit bearings tj d30 shafts and the carrier. but dont quote me.

I was under the impression that the 30 spline count is at the locker end and none of the outter bearing stuff changes.

Going with a super D30 kit locks you into the 30 spline shafts and cheap spares are a little tougher to find. The Rubicon 44 is the only OE 30 spline shafts that will work other than the alloy aftermarket units. If you run the 27 spline, you can use stock XJ shafts as spares to get you off the trail if you break.

you'll be fine with the 27 spline carrier. just grab some newer model shafts that take the 297 joints and have fun

If you want to keep your Full-time 4wd option.. then a locker is out of the question. An LSD, or similar would be needed if you want to keep FT4WD

The Superior Super30 Kit comes with 30 spline inners and 27 spline outers to fit the stock unit bearings. So far as I know, Alloy's Grande Kit is the only 30 spline inner and outer kit. You should be fine leaving it 27 spline inner and outer all the way around with 31's. Me personally, if I had to replace the carrier anyway I'd go with the 30 spline carrier, 27 spline outers, and a nice set of alloy shafts with good joints. I wouldn't mess around with the 30 spline outer stuff myself. Too much hassle and I wouldn't want to be locked in to using their unit bearings. If you decide later that you have to have 30 spline outers, Alloy sells an upgrade kit...

I'd save some money and run the stock axles, and bring some junk yard spares. That way, if something never happens you have extra dough for your locker or what ever. Or if something does happen, say on the trail, you would be able to throw your spare axle in nice and fast then continue having fun the rest of the day. Also, because you're only running 31's the chances of you braking something is much less than 33s or 35s.

Replace your axles, not your gears. That's my train of thought. But maybe because i've had to set up quite a few diffs and know how big of a pain that is.

If you're only planning to run 31's I would do a full circle clip mod and 760 u-joints and make sure there are no sharp edges on the holes in the carrier and I think you will have plenty of strength.

jeeperjohn said:

If you're only planning to run 31's I would do a full circle clip mod and 760 u-joints and make sure there are no sharp edges on the holes in the carrier and I think you will have plenty of strength.

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The PO of my Jeep replaced the u-joints on mine with 760's I think they will be plenty strong for my 31's! Also OP, since you are sticking to 31's and not much lift. I would go ahead and upgrade to a V8 ZJ tie rod.

Johnnie Walker said:

If you want to keep your Full-time 4wd option.. then a locker is out of the question. An LSD, or similar would be needed if you want to keep FT4WD

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Not if he goes with a selectable like OX or ARB.

OP, 27 spline alloy shafts w/5-760x u-joints should be plenty strong for 31,s I've seen guys run pretty hard on stock shafts with the 5-297x u-joints and 35"s with little issue. Hell up until recently I've been running stock shafts and 31"s and have only broken one shaft, but I blame the junk Duralast U-joint on that, and I've busted the spider gears, and bent a housing, I have yet to worry about the R&P.

Thanks to all for the advice. To close this off, I ended up taking PacificEd's advice and went with the 27-spline to keep spares as an easy option, and went with Crash's methodology of keeping the axle as the weak link rather than the R&P. Got an ARB with some alloy axles and 5-760 joints. Based on all the comments, this should be plenty strong. Time will tell.

You're golden. I probably wouldn't even carry spare shafts. Especially if you're not wheeling alone.