31 splin in small bearing 9"? vs 28

[69Early]

I am replacing my 350 open third member with a Detroit true trac and am contemplating going to a 31 splin from the 28 on my small bearing 9" <br><br>Has anyone been running 31's are there any downsides to going 31's in a small bearing?

 

[broncoswede61]

I've got 31 splines in my SB rear....No problems so far.Of course the ultimate would be a BB rear ,but for what I do in the bronco,the extra expense of finding a BB wasn't worth it.

 

[Guest]

If you're going to be spending the same amount of money either way, go for the 31-spline axles. They won't have the same bearing as the big bearing 31-spline axles, but they will be a stronger axle. Be warned, though, that they aren't designed for larger tires. In talking with the guys at Currie, they know of about a half-dozen small bearing axles that have failed when combined with 33" and 35" tires. The bearing pulled right off the axle. They consider this an abuse issue and won't warranty the axles. If at all possible, I'd recommend waitng on the rear end build. Otherwise you'll end up doing everything twice--eventually. Take it from me, I had a SB with 4.11 gears and a Detroit and I was always trying to keep that thing alive. Now many dollars later, I have a BB with 31-spline axles, an ARB and disk brakes. Hopefully I'll never be replacing that thing!

 

[69Early]

Are the failures attributed mainly to the size of the tires? I am running 32MT's and am wheelin mostly on trails, hills etc. Not much crawlin. Did currie elaborite on why the bairing failures rhw whole purpose of going 31 was because I was told they offered much strength? I spoke to Randy's Ring & Pinion, along with Duff and Tom's and they didnt know of any problems. Of course they were speaking from a sales point of view?

 

[rulebreaker]

I have a BB 9 with 28 spline axles. I have found that 28 spline axles are good up to 35" tires. BB or SB they all go bad eventually. I have had two BB go bad in the last year,Shoot hapens what can I say!

 

[c2computer]

I took mine into Currie and they chopped mine and converted it to the BB. If you run the 31 splines with the SB, you will be changing bearings about every 10k miles? This is what I was told from Currie so I decided to spend the extra $ and do it right. It can be done but as with anything, there are downsides to it. I also got the 11 inch drums with it which helps but the ebrake sucks on them.

 

[broncoswede61]

[quote author=c2computer link=board=5;threadid=12316;start=0#91853 date=1040057097]<br>I took mine into Currie and they chopped mine and converted it to the BB. If you run the 31 splines with the SB, you will be changing bearings about every 10k miles? This is what I was told from Currie so I decided to spend the extra $ and do it right. It can be done but as with anything, there are downsides to it. I also got the 11 inch drums with it which helps but the ebrake sucks on them.<br>[/quote]<br>Seem like it would be a combination of conditions to cause bearing failure.....I don't see a connection between spline count and bearing size....I think more important factors would be tire size and if the rear is locked

 

[c2computer]

I am not sure either, except putting the 31 spline in with the bigger tires and keeping the small bearing wears them out quick. Just passing on what John at Currie said.

 

[Hnrys69]

[quote author=c2computer link=board=5;threadid=12316;start=0#91990 date=1040082210]<br>I am not sure either, except putting the 31 spline in with the bigger tires and keeping the small bearing wears them out quick. Just passing on what John at Currie said.<br>[/quote]<br><br>Sounds like he wanted your money to me.

 

[c2computer]

Well the guy who had it done had a Bronco (John @ All 4 Wheel in Riverside) and he said his wore out after 10,000 miles. I belive it, small bearings with big tires and axles not meant for it but who knows. I took his advice and it is working like a charm now so that is all that matters I guess. It was about $250.00 more.

 

[soulflybro]

I have 4.10s and 33's with a SB, a detroit, and 31 spline superior axles. I've had it all for about 10, 000 miles now, and it has alll been perfect. That axle work made the biggest difference in wheeling capabilities, and im 18 years old so trust me i beat the shit out on the dirt AND on the street. I have done many irrational things trust me, and everything has been great so far.

 

[Rustytruck]

It isnt the tire size it is the fact that in order to put in a larger diameter axle into the smaller OD bearing something has to give so they have to reduce the individual inner ball or roller bearing diameter which means they have to spin more times per revolution of the axle then add the extra weight and load that most people who put in the 31 spline axles have, you start to court disaster. It is easy to picture if you think of the bearing as a planitary gear set the smaller inner gear will spin more per revolution and as an added benefit since the radius is so small on the bearing the contact pressure is higher also. On really high loads they go to taper roller bearings to gain more contact patch on the individual bearing load surfaces.

 

[c2computer]

If that isn't a technical explanation I don't know what is. Whatever it means, it makes me feel bette about speding the 250 bucks. ;D

 

[rulebreaker]

I could be wrong and i have been before but I think the 28&31 spline axles are the same diameter where the bearing rides!