9 inch Big vs Small Bearing Strength

[BigBlueBronco71]

I've been doing some research and have found some of the differences between the small and big bearing axles but is the big bearing axle inherently stronger than the small and if so why? Can it run thicker axle shafts, can the bearings support more load, etc.?

I have a small bearing rear and was wondering if it's worth finding a big bearing to build or build what I have, 33/35s, 31 spline, chromo axles shafts, locker, trail capable

 

[Apogee]

If you want a trail capable rig with 33/35's, then yes, the big-bearing axle upgrade would be worthwhile IMO. The bearings have higher load capacities and the axle shaft is larger at 1.531 or 1.562 (SET20 or aftermarket sealed ball bearings) than the 1.378 shaft diameter of the small bearing application. This means more axle strength and rigidity.

 

[DirtDonk]

And less replacement cost too when using the heavier duty tapered style bearings.
The bigger axles for small bearing 9" housings cost more due to the more expensive odd-sized conversion bearing.
http://www.wildhorses4x4.com/category/bronco_rear_axle

No real difference in price when used with standard small and large sealed bearings, but if you're ever in the mood to upgrade, you're ahead of the game with a large bearing housing.

Paul

 

[BigBlueBronco71]

Thanks guys great info,

So when would new heavy duty or extreme duty housings be necessary, like the super 9 or megalodon from WH? Only for an extreme crawler with 35 splines? Seems like they would be overkill for what I want to do, opinions?

Would the best used option be the 66-75 large bearing or would it be worth trying to find a 76-77, how bout the 74-75 medium duty (seems like the odd duckling with the small brakes)?

 

[DirtDonk]

All depends on exactly what you want to do, and how you want to equip your truck.
But yes, generally speaking the Megalodon is one you would definitely save for the extreme setup. Not for your general 33 inch tired street driven Bronco.
But the Super 9 is not a bad price point to get into not only an upgrade to large bearings, but an upgraded housing all around.

Most owners are not beating on their rigs like we did when they were new and we were new too. But if you're going to spend some time in sand dunes, run big tires and high torque engine, or load heavy bumpers, roll cages and all sorts of other stuff to the mix, along with a weeks worth of camping gear, the upgrades are all worth it.
No real need for trusses anymore, like we used to add for those applications.

Again though, at that price point, while a used big-bearing housing would be less expensive, that would depend on your ability to find one. Especially the limited number of '77 housings floating around for sale out there.

Another option however is simply(?) cutting off the ends and welding on big bearing ends. They're readily available and should not be any trouble for a shop that works on this type of stuff.

With open differentials, small tires and light loads, even a 31 spline axle upgrade is overkill. But only by a little.
Add a locker, larger tires or a heavier right foot, and the minimal upcharge for 31 splines is almost a no-brainer.
But 35 spline axles? Back to the type of load and use. Most of us can get by just fine with 31. But 35's are "better" of course...

paul

 

[BigBlueBronco71]

Well I'm 21 and do like abuse my bronco in the dunes and would like to run some decent trails, do donuts and what not ;D so I'd like to build them to handle their own.

So I've read that the housings themselves are weak on the rear end, what problems does this actually cause and why are they considered weak? I don't think that a housing would outright fail and break, do they crack and/or bend causing stresses on the gears and axle shafts?

 

[Apogee]

If you're going to jump your EB in the sand, then you really can't overkill the rear end. A gusseted rear housing would be a good option...full-floater even better. If you don't plan on jumping much, then the 76-77 housing would be preferred, but any of the large brg housings should work for you.

The housings are fabricated and tend to crack or bend first. Cracks can be welded, and when done properly should be as good as new. If not done properly, then you will just be chasing cracks to the end of time. Bent housings can be straightened, but if you run while bent, that can be really hard on the axles, bearings and tires.

 

[DirtDonk]

Yep. The housing is just stamped and formed steel, with some decent sized tubing for the axles. Back in the day, a simple cable or bar truss was added (mostly to fronts, but also to rears) to add some support and keep the flexing to a minimum.
The fabricated "back brace" was a real boon as it was super beefy and you no longer had to sacrifice ground clearance to get the support.

Upgraded housings like we're talking about are a step above and don't necessarily need the extra reinforcing for most of us, but a back-brace is still desirable if you're really going to go out there and beat on it. Or if you're just going to have a little too much fun and are running 35" or larger tires.
As you'll no doubt here around here, they last just fine under quite a bit of abuse for most of us.

Some of the extra features of our Super-9 (http://www.wildhorses4x4.com/product/17600) are:
The use of the later housing centers which are wider for more support.
The centers are V-cut ("fishmouthed") at the axle tube junction for even more support, more weld area, stress riser reduction (or at least a change of the dynamic).
Billet steel big bearing outer ends with the large 1/2" bolt hole pattern.
Spring perches already welded on at an appropriate angle for a modern 10 or 11 leaf pack when used in an EB. Means you are very unlikely to need tapered shims to align the pinion when used with a lift kit. Not sure how far off it would be with stock springs though. No feedback on that yet.
Smaller diameter axle tubes (a good and bad point perhaps?) for added ground clearance.
All at a pretty decent price level actually.

The added clearance with the axle tubes is more a byproduct than by-design. It's pretty much a necessity these days, as nobody we could find manufactures a center housing for use with the original 3.25" diameter tubes. And all the original cores from the junkyards have been picked clean with few exceptions. So other than used, you don't find 3.25" centers anymore.
Still, it's a stronger option than just a stock '77 and later housing due to all the other upgrades.

Hope that helps.

Paul

 

[sykanr0ng]

For the uses you have in mind I would suggest a back brace style truss like the ones Wild Horses and RuffStuff sell.
Those add strength and stiffness but don't cost any ground clearance.

While you are building the housing add some anti wrap spring perches and an extreme duty U bolt kit or RuffStuff 2+ perches.