Bearing heat from grease

I would like to know that myself Joe!! And those piddly little wheels are really rotating at a much higher speed than the tow vehicle! Michael

Joe,

Got few thoughts on this. A lot of boat trailers would only travel <100 kms down to the boat ramp, before being immersed in the briny, and cooled down. Then they would sit near the ramp for the day, and back home. Being full of grease stops the ingress of water, so the integrity of the bearings is preserved.

With other trailers, the preload of the bearings would be more important to prevent overheating, along with the required amount of grease to lubricate said bearing. Too much grease would be better than not enough.

I do 4400kms /week towing trailers, and it's scaring when you happen to check the hub temperatures........sometimes too hot to keep your hand on the hub.

Wonder what others think?

Bob.

I don't know the truth with over packing wheel bearing causing them to run hot....... if you can pack a boat trailer bearing and hub full of grease with no problems then there is your answer.

To little grease can make them run hot, we use just enough grease as there is no point in putting more in and the grease can't go anywhere.

Never heard it a trade school.

If anything more grease will transfer heat to the hub more efficiently....... but a hub should not run hot, if they do run hot it means there excess s friction being generated.

The only thing I can think of is maybe expansion blowing out the seals in the olden days, how seals are designed and the amount of expansion to blow them out I would doubt it.

Me think urban myth.....

Joe.
I like your reasoning. Apparently some people believe too much grease will overheat the bearings on a 4wd but not on a boat trailer. Strange isn't it.

Most boat trailers with the grease reservoir which pumps/hold grease pressure seem to last and they may leak/seep a bit of grease unless the seal is kept in good condition by replacement at service time.

On a 4wd if you put in too much grease it usually finds it's way out of the hub through the seals and can drip off.

I always fill cruiser hubs so the level is above the edge of the two bearing cups, so when hot, the grease can flow through the bearing rollers and lubricate them.

Less grease means no flow through the rollers and the rollers squeeze the grease away and then they run metal to metal with little or no grease, then they get hot or worse.

Some cruisers from the factory don't have much grease in the bearings at all, some have done wheel bearings shortly after being purchased new.

I know of one new cruiser which didn't have enough and the dealer greased them shortly after purchase. The problem was the person doing the job tightened the bearings too much and the hubs got hot from being tight. Iif driven more than 4 km they got hot. If on a trip, goodbye wheel bearings or worse.

Grease and correct adjustment is ok though.

Ross M

Wondered about this myself as I now put bearing buddies on my work trailer. It sometimes takes a dunking into slurry on minesites. I give them a squirt of grease after every trip and check them regularly by touching the hubs after driving for a couple of hours

It Must be an Urban myth.

Cheers Wilko

If you look closely at a boat trailer hub, the seals are often put in back to front.
This enables the seals to keep the water out rather than keeping the grease in.
That's why boat trailer hubs are filled with grease, the excess will push past the seals as necessary.

Disco.

Greasing of bearings can get very technical.......at work, with large electric motors, we have tech blokes come in and use vibration monitors and can tell if a bearing needs 1,2 or 3 pumps of grease... !!! but will also pickup if the bearing has been overgreased..

Now, for a trailer, it isn't this technical, and overgreasing isn't really a problem, as the large area around the bearings means the bearing itself doesn't get "pressurized" with grease....although (except for boat trailers, when water exclusion is the aim of the game ) you don't really want to fill up the cavity with grease, because 1. it's a waste of grease and 2. the grease won't flow anywhere ( unless it's overheating )

All bearings should only be lukewarm to touch ( unless the brakes have been operating ) in ideal conditions..

Are all the newer vehicles/trailers still using the greasable type of bearings, or have some of them gone to the sealed units?
Only reason I asked is that when I replaced the bearings on my bike a few months back, they were sealed, and I believe I can change a few other bearing over to the same.

Here's what the folk at Timken have to say about it >>

"A very high percentage of all bearing damage can be attributed to inadequate
lubrication. Although a very broad term, inadequate lubrication can be
classified into eight basic categories:

• Overfilling
• Underfilling
• Incorrect grease
• Mixing greases
• Incorrect lubrication systems and intervals
• Worn-out grease
• Water contamination
• Debris contamination

Overfilling
Overfilling a bearing with too much grease can cause excess churning during
operation and high temperatures, resulting in overheating and excess grease
purging (leaking) – see note below. Overheating occurs because the heat
generated cannot dissipate correctly, continually building until damage occurs.
As the operating temperature of the bearing rises, the oxidation (breakdown)
rate of the grease sharply increases – doubling every 10° C (18° F)."

And>>

"Required Grease Quantity
To avoid the generation of heat, the bearing must not be over greased.
The required quantity of grease is based on the free volume of the bearing
calculated as follows: V ˜ p/4 (D2 – d2) (T) – M/A"

Source>> http://www.timken.com/EN-US/products/bearings/productlist/roller/cylindrical/Documents/BDABrochure5892.pdf


I'll take their word for it ;-)


:)

Not an answer to your question but when I suggested to my mechanic to fit bearing buddies to my boat trailer he did not recommend it.
He said that you are better to just pack the bearings correctly, the problem with the bearing buddie type product is that when you pump excess grease in you blow the back bearing seal out and that allows water ingress .

Sounded like a feasible explanation to me.

Thanks heaps for the replys all, it has been a question i have wanted to ask for a while as i have read many threads about bearings and packing them and most go on about "over-filling" them as a big issue, i now think it may well be a myth, yes the factorys only put a dash in these days but that may also be a cost cutting process also, they would use 5 times the grease if they filled them i guess ......
My thoughts now are it depends on the RPM of that bearing, in a high RPM bearing you can NOT fill it more than 30%, in a low RPM such as a wheel you can fill them, my thoughts now are to fill them as full as i can, it will help with water ingress as there simply is no room for water to get in if full, it is very low RPM si it will probally assist with getting rid of heat and i am now thinking it is the brake heat i am feeling as it is bolted right up to the hub and they get REALLY hot and the heat will transfer to the hub as it is bolted to the disc ...
I have often wanted to put a grease nipple on my hubs and give them a couple of squirts every trip, 2 years ago i had a dry bearing squeaking and got to it just before it failed and came apart, at Wycliff Well actually, pulled it apart and it was dry as a ..... and black and burnt, i cleaned it up as best i could and packed in the grease, re-assembled it with very light per load, picked up a new set of bearings at Tennet Creek and decided it drove well, was still reasonably cool, same temp as other side, and was to bleedin hot outside so we just drove on, drove from there all the way home to Doomadgee and ended up replacing it 6 months AFTER we got home and it was still blackish but well greased and lot no pre load ....
All bearing failures that i have seen and had were dry of grease, some with muddy water ..... never have i seen a fully packed bearing fail, on a car anyway ...
So i am gunna pack em as full as i can get from now on and see what happens .... keep in mind if you pack the free wheeling hubs full they wont work mmmm bugger maybe just lock em im an leave em ....
Thanks all, very interesting reading....
Myth is "busted"
Joe

And then of course there is the subject of oil filled instead of greased wheel bearings, but I guess that is a subject for another day (;-))

Cheers
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