Technical Why wheel bearings are greased

Accordng to the ASE mechanic who just did a brake job on my truck - he was taught at school that the grease helps move the grit & dirt away from the bearing surface.

To demonstrate - he put a dab of grease in his palm - added some grit - swirled it around - the grit moved it to the outside.

Never heard that one before ....

Jim

 

How does grit and dirt get on the bearing surface?

 

From dirty hands

 

If a seal fails I would imagine


Jim

 

Wheel bearings should be cleaned and repacked at least 30,000 miles due to them heating up & cooling down thousands of times the grease just wears out.

We lost a spindle on the wagon years ago to lack of maintenance. HRP

 

Grease (and oil) provides a film to separate the bearing from the race. Maybe it keeps the grit to the side, eventually, but cushioning the metal surfaces is the main objective.

 

I give my dust caps a bit of grease every oil change. Haven't had a bearing failure in years.

Sent from my LG-TP450 using The H.A.M.B. mobile app

 

One of the main functions of grease is to seal a bearing to prevent dirt ingression. This is more common in plain bearings with no seals or simple cord ring seals, but it is a main function of the grease. I've never heard of it moving contaminants out of the bearing before. Like Engine Man asked, how is the grit getting into the bearing to begin with? I'm skeptical.

 

And water. One of the steps in the OEM manuals and bearing manufacturer instructions is to fill the hub cavity with grease to a level even with the inner bearing race. Also, fill the dust cap partially full. Grease doesn't really move, so it's not for lubrication, it's doing double duty as a filler in those instances near as I can figure. When I was in the .mil aircraft wheel bearings were inspected & repacked every six (6) months no exceptions.

 

dont grease them ,you have metal on metal .no lubrication,soon to fail....llll

 

I’ve heard of oils and greases holding contaminants in suspension but never a “smart grease” that can move contaminants out of the way.

I have seen greases that have failed due to heat and lack of maintenance.
Also seen bearings and bushings fail and contaminate grease with there own failure.
But if outside dirt is getting in I would be looking at why, not passing the job on to the grease to keep things clean


I call shenanigans on what this mechanic showed you as far as it’s the greases job to move contamination. Seems more like centrifugal force doing its part on solid objects in a fluid ( aka grease)

 

Pushes dirt out... sounds like BS to me. I dare any of you to run your car without dust caps on your front spindles and see how long your wheel bearings last. All it takes is a speck of grit and bearings are toast. I have had people doubt me on this. Their wheel bearings failed within a week!

 

And all these years I thought that oil or grease was for friction reduction and cooling.........

 

Proving my belief formed at age 7 that the school was a stupid place teaching mostly stupid stuff...
... and again glad I didn't pursue it beyond expected minimum.

 

The purpose of grease is to make shop rags dirty.
The purpose of grease is the seal under finger nails.
The purpose of grease is to stick nuts in a socket.
The purpose of grease is to contaminate braking surfaces.
The purpose of grease is to remove pilot bushings.
The purpose of grease is to prevent rust.

Grease does a lot of things, is that it's purpose? I can clearly demonstrate the above examples like your mechanic did. Doesn't make it thee purpose

 

If my ASE mechanic son tells me that, I'll whack him upside his head

 

Machine design principles mention lube film thickness, and further divide lubrication into rheology (not theology), and tribology (to rub). Now back to our regular sponsor!

 

Through my many years in automotive repair and trouble shooting I have run into a few people that have re-written the book on basic principles of automotive mechanics. They seem to get the job done but have developed some strange theories about how things are supposed to work.

 

Time to find another mechanic. Wondering why we buy sealed bearings? Time to ditch your bearing buddys. I never did believe in bearing buddys anyway. Not even for a trailer. Back in 54 they taught us to use the plam of our hand to hold the grease & pack the bearing.

 

tri·bol·o·gy
trīˈbäləjē/
noun

1. the study of friction, wear, lubrication, and the design of bearings; the science of interacting surfaces in relative motion.

I'm a member of the Society of Tribologists and Lubrication Engineers.

 

Old school!!! That's the way I do it.....

 

I agree with Bob 100% there, it's time to find another mechanic if he spews that kind of nonsense.

I'll use bearing buddies on a boat trailer but don't see the need anywhere else.

Like Bob I was taught to pack a bearing by scooping the grease in between the rollers by passing it though the grease in the palm of my other hand and taught a lot of students to do the same over the 13 years I taught mechanics.
One thing my shop teacher a Mr Bill Palmer taught me the first time I packed a set of bearings in 1962 is that you never wash a bearing that you intend to reuse in solvent. The only times I have ever washed a bearing are to be able to hand it to a customer to show that it was indeed bad. I've had damned few wheel bearing problems over the past 50 something years and never had a customer that I had packed the wheels for come back with a bad bearing.
Before someone pisses and moans that you have to wash a bearing think about this a minute.
Solvent in a solvent tank will always have some dirt and contamination suspended in it.
You cannot get all of the solvent out of a bearing you wash in solvent and it will prevent the grease from sticking to the bearings or dilute it.
By pushing the grease through the bearing you push the old grease out the other end until you just have clean grease coming out to be wiped off.

 

Snot, mayonnaise, or Cheez Whiz will do the same thing. Wanna pack your bearings with any of those?

I'm not going to piss and moan, but any time I've re-greased ball or tapered roller wheel bearings I've washed them off in solvent, then rinsed them off in clean gasoline, and blow dry. Then re-grease and install. I really don't want to say that I've never had a wheel bearing failure as it may well jinx me, so I won't say that.

 

Use a blow gun.....

 

I believe I would use a different shop from now on

 

Most big truck bearings ride in 90w oil, as do most trailers, although some are going to greased bearings.
Any time I have an oiled bearing out, I fill it with grease before it goes back in. Why? To give it lubrication until the oil gets up to it. The oil will wash the grease out and mix with it over time. Have seen bearings put in with only oil, then the truck sat a few hours and the oil dropped off, and when the truck left the bearing got hot before the oil worked back into it.

 

An error I'd see as a high school pumpjockey, was using air, to Spin dry a solvent cleaned bearing.

 

The latest semi trailer hubs use a special lube that's about the color of honey. Its sole purpose is lubrication of rolling element bearings, unlike gear lube that has to function both as a bearing lube and as a lube for sliding contact that occurs in gear sets.

They also use dead length spacers between the inner and outer bearing cones, so rather than the old way where you tighten to 75 ft-lbs to remove all play and then back the nut off by 1/6 to 1/4 turn, you just torque the nut to something like 400 ft-lbs and put a locking device on it to prevent it backing off. The spacer sets the bearing clearance, and the assembly is warranted for 700K miles.

 

I seen dust caps with zerk fittings once.... I thought it was a great idea....