oil filled hubs for camper trailers

Gday String
You are no more likely to brake a sight glass than loose a grease hub cap. I imagine there are people on this site that have had the site glass damaged and also lost a grease cap. You have to read between the lines on that one.
Trucks use them and have done for 40 years that I know of with no problems. The only difference is that truck hubs spin a bit slower than your van wheels.
Earth moving machinery use oil in their hubs as well and have done for who knows how long.

String.
I would be concerned with the quality of the average hub to axle seal. Most larger machines have substantial seals and as mentioned rotate slower.
The adjustment is not likely to be loose on large stuff whereas many trailers seem to have a tendency to become loose. The axle and the seals then move radially and the seals don't appreciate that too much and subsequently begin to leak.
In most cases the overall integrity of trailer axles, hubs and adjustment method isn't up to the same quality/standard as the tow vehicle.

Cheers
Ross M

String - Well, like so many ideas, there are pros and cons for both. What we're all looking for is something that has excellent sealing against dirt and water, is low maintenance, reasonably priced, tells us when a bearing is getting crook, is as friction free as possible, and is something we can get parts for easily.

Grease comprises lube oil held in suspension in a "filler" compound - usually a metallic or synthetic soap (polyurea) compound that is stable and has properties that suit its designed use. If grease is left sitting for an extended time, the oil tends to drain out of the filler compound.

You can get greases that resist high temperatures, that resist water-washout, that resist chemicals, and greases that are thick or thin. Thick greases stay in place better, thin greases flow better around surfaces to be lubed. Thick greases have higher levels of friction.

Oil baths for bearings are usually best when fairly constant turning is the order of the day. Thus you see oil bath bearings on Interstate trucks, because they're moving constantly. The small reduction in friction of an oil bath bearing pays off only with high annual kms.

The biggest failure point in wheel bearings is the inner seal. It cops a hiding from debris, sand, stones, and general road trash thrown up by the tow vehicles wheels. Once the inner seal fails, dirt finds its way in to the inner bearing and it fails rapidly.

Water ingress into the bearing is another huge problem. Once water gets inside the hub, and the trailer or 'van sits for a week or two, corrosion starts in the bearing race or rollers. Bearing failure soon occurs once these surfaces corrode.

An oil-filled hub has somewhat better sealing than a greased hub, because it's fully sealed, and the oil is lubricating the seal surfaces constantly.
Grease tends to be a poorer lubricator of seal lips and seal surfaces.
It's harder to get water inside an oil-filled hub, as compared to a greased hub.
However, any moisture getting inside an oil-filled bearing hub, is going to cause corrosion, exactly the same as a greased hub.

As far as bearing failure indications go, oil-filled hubs do give you an ability to see bearing flecks in the oil, and thus be alerted to a potential or imminent bearing failure.

Greased hubs show little sign of impending bearing failure, as many people have ruefully found, when a trailer or caravan wheel suddenly falls off. Regular bearing checking and bearing maintenance is crucial for greased hubs. I have never lost a trailer or caravan wheel, because I check wheel bearings frequently.

In all my years of trailer and caravan ownership and use (about 46 yrs from memory), I found one thing that was of major advantage in preventing greased trailer and caravan bearing failures.

That one thing was - installing a thick (10mm), large diameter (same diameter as the inner seal) heavily-greased felt washer, tightly on the axle inside of the hub, right up against the inner seal surface.

This heavily-greased felt washer then acts as a labyrinth-style face seal, that physically protects the inner lip-type seal, and which also acts as an additional barrier to dirt and water ingress.

Essentially, the grease-style hubs are a cheap, proven concept, that works effectively, and which are highly suitable for reasonably regular intermittent use. You can improve on the reliability of these style of hubs by adding the felt seal as I previously mentioned.

The oil-filled hubs are higher initial cost, and can yield small fuel consumption savings when high useage is common (regular, high kms). They offer a somewhat higher chance of detecting bearing failure, that is not available with a greased hub - and they do offer a higher level of sealing against water entry into the hub, if you do a lot of deep water crossings or boat launching.

Greased hubs have ready availability almost anywhere, whereas oil-filled hubs are less-readily found when spares are needed. I would hazard an educated guess, there's less need to repair oil-filled hubs. The window in oil filled hubs is perspex, as I understand, not glass, and I cannot recall ever having seen one broken. I'd imagine you'd have to do something out-of-the-ordinary to break one.

Cheers, Ron.

Have seen it once , the b/inlaw throwing the ratchet strap over the load [semi trailer] ,the weighted end smashed the view glass/perspex .......oops ....1 in ten million chance he reckoned ,but absolutely no problem getting a spare so it must happen....

There are all sorts of "gadgets" sold to improve the reliability of trailer bearings, they sell very well among the boating community.

BUT

there are those that believe that there is no substitute for proper bearing service, good quality bearings and the right grease....and of course bearings and hubs of adequate load capacity.

The fact is, the bearings on trailers are designed to be greased, the hubs and the seals are designed around grease.

It is pointless to discuss what is used in heavy trucks and earthmoving equipment, because those bearings and their housings are designed for whatever lubricant they are running.

We don't hear people discussing all sorts of gadgets to replace grease in the front wheels of their tow vehicles so why do we hear so much about them on trailers.

A lot of what we hear about these "gadgets" the reasons and the advantages is mostly sales spiel.

As far as grease seperating.....well start with the brand and type of grease you use, then think about the amount of seperating involved...realy ya think all the oil has come out of ya grease......its a pretty crook grease if that is the case.
Yeh there may be some oil that comes out of the grease...but what proportion.

These days for most uses, Blue lithium complex grease ( LMX, APXT, boating grease...castrol names) is all over the previous options like a rash.
It is way more water resistant than both bentonite ( HTB) and old style lithium ( LM).
It has much better high temperature performance than old style lithium, and while not as high temperature tolerant as bentonite..unless you are running ya disks red hot it will be more than adequate on temperature.

While there may be a very small pool of oil in the middle of my bucket of LMX, If I have not been in there for a while, the grease is still, standing up in firm ridges where my fingers went in months ago.

I do not believe sepeartion of grease is a problem in hubs, if it is a decent grease it should be held in the bearing races and will be remixed in the first revoloution of the wheel.

Serioulsy have you ever taken off the bearings and found the grease all sitting in the bottom of the hubs.

People rave on about stuff getting into the hubs......if your caps and seals are in good conditon, water will not get in unless you immerse your hubs in water.

Even then very little if any at all will get in if the bearings are allowed to cool before the wheels are immersed.

AND
In a greased bearing, neither the seals nor the caps have any role in retaining the grease, their sole purpose is to keep dust dirt and water out.

SO, if you lose a dust cap and you have greased bearings, you can cheerfully drive home or to somewhere you can get a cap.....if its an oiled hub and ya cap disappears or fails OR you have a seal failure you have no lubricant.

Seriously.....forget the gadgets...look elsewhere for the real reasons of bearng failure and learn to maintain your bearings correctly..

cheers