I have heard that you can over grease a bearing. Anyway, I bought these 1200 pound capacity casters (4" dia x 2" wide steel wheels) for the back of my motorhome where it sometimes drags tail on driveways. I mounted them yesterday and then greased them. They still made some metallic noise so I added more grease until they got quiet. But now they don't spin as freely. I think I put too much grease--way too much. But I am thinking it doesn't matter because they do turn fairly easily and are only going to be used on occasion, not continually. What do you think?
Too Much Grease?
- Thread starter TallPaul
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Leave it. It may be overgreased but it won't hurt anything. In fact, it will help keep moisture out of the caster bearing surface, especially since, as you say, they don't get used much and will sit for long periods of time without ever being rotated.
I also would leave them alone since low use bearings aren't that critical, but for future ref. a sealed bearing housing typically should have ~60% of it's total capacity filled. More won't hurt, but it can start to create counteracting friction when filled more than 60%. Too much grease can also create pressure and can help to cause the seals to fail.
Once the seal is violated, it makes it much easier for the grease to seperate and the base oil to escape, leaving sluggish soap.
The bearing with the proper amount, and a good seal, has the situation that allows base oil that has fallen out of suspension to reverse back into suspension.
Once the seal is violated, it makes it much easier for the grease to seperate and the base oil to escape, leaving sluggish soap.
The bearing with the proper amount, and a good seal, has the situation that allows base oil that has fallen out of suspension to reverse back into suspension.
Well, I guess greasing is an art. I never liked greasing. I always have the shop hit all the grease fittings whenever I have a vehicle in for service. I'll do the oil changes though.
You trust shop mechanics to grease your car properly? wow.
On a slightly different note, I work with a bunch of guys who overgrease shaft bearings in air handling units on a regular basis. As you noted, it creates drag on the bearing. In our application, it creates heat, the grease shears, separates and wastes the bearings. The building is three years old and we replace bearings like candy. My room upstairs where no one else has access, everything is fine.
In your application, the grease will be ok. Our stuff runs 12 hours a day.
On a slightly different note, I work with a bunch of guys who overgrease shaft bearings in air handling units on a regular basis. As you noted, it creates drag on the bearing. In our application, it creates heat, the grease shears, separates and wastes the bearings. The building is three years old and we replace bearings like candy. My room upstairs where no one else has access, everything is fine.
In your application, the grease will be ok. Our stuff runs 12 hours a day.
I trust select shops and do so because I am not very competent in geasing as you can gather from my initial post. When I grease u-joints I like to see it come out all four ends. Not sure that is good.
too much grease is awalys better than none.
Kestas
Staff member
TallPaul, u-joints operate differently from your typical bearing. A typical bearing rotates and drag and heat generation can be an issue. The rolling elements of a u-joint just vibrate in place.
From the SKF catalog:
"An excess of lubricant will cause the operating temperature to rise rapidly, particularly when running at high speeds. As a general rule, therefore, only the bearing should be completely filled, while the free space in the housing should be partly (between 30 and 50%) filled with grease.
Where bearings are to operate at very low speeds and must be well protected against corrosion, it is advisable to completely fill the housing with grease."
From the SKF catalog:
"An excess of lubricant will cause the operating temperature to rise rapidly, particularly when running at high speeds. As a general rule, therefore, only the bearing should be completely filled, while the free space in the housing should be partly (between 30 and 50%) filled with grease.
Where bearings are to operate at very low speeds and must be well protected against corrosion, it is advisable to completely fill the housing with grease."
This thread reminds me of the time I saw a guy driving a late model Chevy pickup with two swivel casters bolted to the back bumper. At the time I remember thinking it was the strangest thing I had ever seen.
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I've seen heavy casters on the rear of big motorcoaches on several occasions. Seems like a good idea to me. And, yeah- I wouldn't worry a bit about over-greasing those as they'll rarely be used... heat will be a non-issue. You main concern shoudl be preventing corrosion- and, to that end, over-greasing is probably preferable.
About u-joints. Here's my rule of thumb- engineers 'round here may or may not approve, but it's worked for me:
If the u-joint in question is fairly new and there's no visible sign that grease has ever gone past the seals, then I just give it a squirt or thre of grease (depending on the size of the joint) and call it good.
If the thing is a few years old and I can see that grease has already made it past the seals, then I pump grease in until I hear the air "pop" out of all 4 seals.
If the thing is old junk and/or somebody has obviously made a habit of over-greasing it, then I pump grease in until it comes out all 4 seals.
Never caused me a problem.
About u-joints. Here's my rule of thumb- engineers 'round here may or may not approve, but it's worked for me:
If the u-joint in question is fairly new and there's no visible sign that grease has ever gone past the seals, then I just give it a squirt or thre of grease (depending on the size of the joint) and call it good.
If the thing is a few years old and I can see that grease has already made it past the seals, then I pump grease in until I hear the air "pop" out of all 4 seals.
If the thing is old junk and/or somebody has obviously made a habit of over-greasing it, then I pump grease in until it comes out all 4 seals.
Never caused me a problem.
I have a tendency to over grease my drive shaft...all it does is get all over the place.
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