First, I'd like to start off with the bits of information I have been able to glean off the net about Hub Unit Bearings, and share some observations and opinions of mine mixed therein.

These type bearings were apparently called Integrated or Live Spindle hub assemblies by the manufacturers for a while, but the 4X4 and off road types kept calling them Unit Bearings so much that the name stuck even with the engineers.

It seems the basic reason to have them is the following, by order of importance to them: (depending on if it is a engineer or a bean counter)


- lighter weight, resulting in better payload and better fuel economy, which equals better environmental results. (they could be considered the 'GREEN' bearings of the new century)
- A more rigid assembly in a smaller package from computer aided design
- Simplicity and speed of assembly line operations
- Base cost of entire assembly to do the job
- Reduced inventory, handling, and shipping costs
- Higher manufacturing tolerance, which increases reliability and reduces after sale callbacks
- Longer service life and no possibility of improper in the field maintenance equates to safer conditions for the occupants

To make them compact and save weight, the unit bearings have the bearings face to face with very little room between them. In the past, this was frowned on because of twisting sideways loads produce a leverage that causes them to deflect.

However, with the Unit bearing, they use fairly large diameter bearings to resist this twisting force, and this allows them to be closer and more compact.

Being more compact, the assembly can be as rigid as before and have less weight.

Now there are probably some benefits that I have not mentioned, but those are the main ones.

Looks pretty good, and it really is, considering that the population of the US as a whole has become less and less inclined to develop and understand the skills of proper automobile assembly/dissasembly/maintenance. This problem is even more pronounced in developing countries (even China) as they have not had a long history of mechanical development in their cultures. ( The automobile love affair for many decades)

So, the hub unit bearing solves a great deal of issues for the engineer, the attorney, and makes a better bottom line for management and stockholders. Safety, Economy, Liability, and cost/profit.

Now let us look at what we, with our Trucks and Excursions, would consider the downside of the Hub Unit Bearing.

When a engineer develops a part, assembly, or a product, The ultimate and idyllic goal is to produce the unit with the least weight, cost, time, and materials. Always seeking the most elegant solution. This, of course, is usually something they cannot have, as the real world is usually a bit more unforgiving. So they add more material, and extra gusset, larger parts, etc. to handle that level of abuse.

At least that is the old way it was done.

Now we have a world where the engineer sits in front of a monitor and computer models the part. Not just merely creating a drawing in AutoCAD, but using computers to analyze the strength and stresses to a very fine degree that the part will have in the real world.

This means they analyze every last one of the stresses that the bearing will have when turning on the highway at 60 mph, expected stresses over bumps, braking, etc. This creates a library of expected stresses the unit bearing will have.

Notice the word 'expected'. The vehicle is expected to have a maximum weight, a maximum cargo, a maximum speed, and maximum stresses. The part is expected to have strength, rigidity, and capability to withstand those stresses. That level, plus a 'safety factor' is what the unit bearing is designed for. The modern part is shaved down to the bone minimum necessary to do the job and still be reliable and safe.

Now, if you and I operate our vehicles in the parameter envelopes that were set forth by the designers of the vehicle, it should last a very, very long time. Do not overload, do not go above the speed, do not tow above a certain amount, do not change the tire diameter. Just Keep It Simple.
But, because of pressures of costs, weight, economy, and profit, they cannot build for all situations.

Of course the engineers are not fools, some things will need a greater safety factor just because someone will tow too much, go too fast, and change the tire diameter, or go rock crawling up a 75 degree slope just for the fun of it.

OF course there are folks like us that will take the vehicle and make it do things it was never meant to do. That is where the parts and reliability start to fail.

Overloading the front axle and bearings with a heavy aftermarket front bumper, winch, and towing a heavy trailer with a weight distributing hitch while carrying 1500lbs of stuff inside the cab while using tires that are 25% larger than design can take it's toll on bearing parts pretty well. The Unit hub race housing can deflect, causing seals to open minutely at the top and let contaminates in. The bearings can and will heat more than normal, Braking heat will be higher, which heats the bearings and reduces seal life. plastic bearing cages can overheat and deform. Larger tires can vibrate more, causing excessive hammering in the races.

All in all, not a good scenario for the bearing, and since it is a sealed unit and cannot be repacked, or the seals replaced, it does not ever get a break. The life of a abused unit bearing is downhill all the way.


Now, what is the alternative? Well, the free spin kits, of course. They have benefits too.

- Repack able bearings
- Replaceable bearings
- Seals can be replaced
- Can take tire abuse better
- Stronger -more metal - less failure modes and deflection
- do not have the Shift On the Fly issues of reliability.
- cheaper wear parts.

And negatives:

- Higher initial cost.
- More frequent and higher maintenance. ***
- Loss of the convenience of Shift On the Fly.
- Sticks out of wheel farther (is able to be hit by obstructions easier)


*** - This is really a subjective thing. For the 2005 Ford Excursion 2WD, It has conventional front bearings. The Ford Scheduled Maintenance Guide severe duty schedule for repacking and inspecting the bearings is every 60,000 miles for normal duty, and 30,000 miles for severe or towing duty. The unit bearing in the 4WD vehicles are scheduled to have the needle bearings greased every 30,000 miles. and every 15,000 miles in 'off-road conditions" Copies of these schedules can be emailed on request.
So you can see, according to the manual, you are supposed to take the unit bearing out fairly often for bearing maintenance. at least as often as standard bearings need repacking.


So that leaves me with a subjective decision. Which way to go.
I currently have a broken drivers side outer axle shaft, a broken Automatic Hub lock, all done due to my towing a very heavy trailer off-road. Not what the designers intended.
I also have oversize tires, with the possibility of going larger. Again, not what the designers intended. Then there is the heavy Buckstop bumper up front.

Last but not least by far is the 4.56 ratios that I have in the axle. A higher ratio than made by the manufacturer of the axle, causing a higher stress level on the bearings than they were designed for, especially when I do my off road RVing.

It looks like the OEM bearings are just waiting to fail on me.

But what about cost? Timken Hub Unit Bearings can be had for around $350.00, so I can replace them both for $700.

Throw in about $250 for a Auto lock hub.

That may very well be the way to go, just to save some dollars, BUT.....

I have that broken axle. It shows that I need stronger axle shafts. That means aftermarket 4340 shafts inner and outer.

The Dynatrack or Spyntec have new 4340 axle stubs in the kit. So to compare:

Keeping the Unit bearing arrangement: (No seals shown as I already have them)

$250 lockout
$700 for bearings
$360 for outer axles

$1310 total

Considering that the Dynatrac or Syntec are in the range of $1550 to 2100, it pretty much makes it a no brainer. I end up shelling out an extra $200 to $800 Than I was going to spend anyway and get the reliability and strength that I need.

I just lose my really cool Auto locking hubs. Sigh..... (Yes, I'm spoiled)


So the only thing left to decide, is ....Which one?


Some light reading:


http://eb-cat.ds-navi.co.jp/enu/jtek...8e/168e_03.pdf

http://eb-cat.ds-navi.co.jp/enu/jtek...8e/168e_03.pdf

http://www.tec.nsk.com/weblibrary/li...%20Swaging.pdf

2000 Ford F250 Super Duty 4x4 Truck- 4Wheel & Off-Road Magazine

https://www.ford-trucks.com/forums/1...some-info.html

 

I really want/need to go to a free spin kit before I lift mine with 37's, so I feel your decision pain.
The timken unit bearing assy's. can be had @ rockauto for between $183-$203. FWIW. if you go that route.

 

Yes. the costs are somewhat less going the unitbearing route.

I just went through a long conversation with my wife, describing the entire dilemma and trying to present it in a unbiased way to get her opinion.

Since it is a issue we both have to pay for, I needed to see her view, of course.

She came to the same conclusion that I had, that since we will be keeping the Ex for many years to come (hopefully), to go with the reliability and strength of the free spin kit.

Since this vehicle tows our trailer, I was deeemed worth it for the reliability and Safety.

Even with high modification costs, a solid, well maintained and paid for Ex beats the hell out of a new Superduty with $600 to $700 dollars a month payments.

 

I don't for sure recall the fellas name, I think it was Scott, with the blacked out X, upgraded front and rear bumpers. He had installed the free spin kit and I'm sure you could try to get in touch with him and ask his opinion on it before going ahead.

When I need unit bearings I may go this route. I had just replaced my ball joints and a few weeks ago and in the process realized my bearings were shot, and started wearing the stub shafts. I was under a time constraint and had to leave for a week of work that weekend and had 2000 miles of road to cover. I had my old bearings that I replaced 1.5 yrs ago because of a bad abs sensor so put those back on. So once these pack it in I will look at the free spin kit without the ball jnts. Under my regular maintain I was removing the bearings once every year to grease the needle bearings as I was going fishing in the summers thru a large water hole, about 3/4 depth of tire and 30 ft long. And yes the fishing was worth it. Lol